**4. Copper(I) schiff base complexes**

Copper(I) Schiff base complexes were generally prepared by the reaction of a CuX, where X = halide (Cl-, Br-, I-), pseudohalide (NCS- , N3 - ), or [Cu(CH3CN)4]Y (Y = the non-coordinating anions (ClO4 - , BPh4-) with a suitable Schiff base ligands in an acetonitrile solvent, followed by room temperature stirring under an N2 or air atmosphere [41-62]. In these complexes, Schiff-bases act as chelating ligands and cause the geometry around the copper(I) atom will be distorted tetrahedral.

Several different crystallization techniques have been used to grow crystals of copper(I) complexes with Schiff base ligands. Some of them are:


Structural Diversity on Copper(I) Schiff Base Complexes 169

By changing the Schiff base ligand from Meca2en to Phca2pn (L10), ca2en (L12) and ca2ph (L18), dinuclear copper(I) complexes [Cu(Phca2pn)I]2 (2) [49], [Cu(ca2en)I]2 (3) [51] and [Cu(ca2ph)I]2 (4) [58] (Scheme 17) have been prepared. Slow diffusion of diethylether vapour into the concentrated acetonitrile solution at 298 K gave suitable orange crystals (2 and 3), while dark red crystals of complex 4 were obtained at 273 K. The coordination geometry around the copper ion in 2 and 3 is distorted tetrahedron formed by two N atoms from the Schiff base ligand and two iodine substituents. The CuIN2I2 tetrahedra

share iodine atoms which therefore double-bridge the neighboring copper(I) ions.

**I I**

However, the chelate N-Cu-N angle in 2 (100.17(12)°) is larger than the corresponding angle in 3 (82.7(3)°), while the I-Cu-I angle in 2 (104.517(17)°) is larger thanthe corresponding one in 3 (119.65(4)°), making the distortion of the tetrahedron considerably larger in (3) because of restricting bite angle of the chelating ligand. The N-Cu-I bond angles range from 100.53(9) to 122.48(9)° in 2 are similar to the corresponding angle in 3 (103.8(2) – 121.8(2)°). The bond distances Cu-I (2.7264(6) Å) and Cu-N (2.055(3) and 2.065(3) Å) in 2 are similar to the corresponding bond distances in 3 (2.6903(14), 2.069(7) and 2.085(7) Å, respectively). The dinuclear unit in these complexes is centrosymmetric with crystallographic center of symmetry located between the two copper(I) ion. The distances between the two copper(I)

The reaction of equimolar amounts of bz2en (L7), phca2en (L14) and Phca2-dab (L17) at the presence of copper(I) iodide in acetonitrile at room temperature yielded mononuclear

dab)2][[CuI2] (7) [61] (Scheme 18). Slow diffusion of diethylether vapour into the concentrated acetonitrile-dichloromethane solution for 5, acetonitrile solution for 6 and

The Schiff base ligand Phca2-dab (L17) have two different phenyl rings (the inner and outer phenyl rings) [61]. They play different role in the arrangement of the cations and anions of [Cu(Phca2-dab)2][CuI] (7). As a result, a one-dimensional net of 7 molecules is generated by 4-PE (fourfold phenyl embrace) including Ri rings (Fig. 1a). The Ro rings are not involved in the 4-PE local interactions. The [CuI2]- anions in the crystal structure are located in the space

**N**

**N**

**Cu**

**I I**

**N**

Scheme 17.

**Cu**

2 3 4

**N**

**N Cu**

**N**

**Cu**

**I I**

**N**

] (6) [54] and [Cu(Phca2-

**N Cu**

**N**

**N**

copper(I) complexes [Cu(bz2en)][Cu2I4] (6) [47], [Cu(Phca2en)2][I3-

chloroform solution for 7 at 298 K gave suitable dark red crystals.

between Ro rings of the two adjacent cations (Fig. 1b) [61].

**N**

ions are 3.372(2) Å in 2 and 2.635(2) Å in 3.

**N Cu**

Scheme 15.

#### **4.1 Copper(I) complexes with symmetric bidentate Schiff base ligand 4.1.1 Copper(I) iodide complexes**

The reaction of equimolar amounts of Meca2en (L15) at the presence of copper(I) iodide in acetonitrile at room temperature yielded yellow microcrystalline powder of mononuclear copper(I) complex Cu(Meca2en)(CH3CN)I (1) (Scheme 16) [56]. Slow evaporation of the solvent, 1:1 *v/v* chloroform:acetonitrile, at 273 K gave suitable yellow crystals. The coordination geometry around the copper ion is distorted tetrahedron formed by two N atoms from Meca2en, one N atom from acetonitrile and one iodine atom. The Meca2en acts as a bidentate ligand coordinating *via* two N atoms to the copper.

Scheme 16.

By changing the Schiff base ligand from Meca2en to Phca2pn (L10), ca2en (L12) and ca2ph (L18), dinuclear copper(I) complexes [Cu(Phca2pn)I]2 (2) [49], [Cu(ca2en)I]2 (3) [51] and [Cu(ca2ph)I]2 (4) [58] (Scheme 17) have been prepared. Slow diffusion of diethylether vapour into the concentrated acetonitrile solution at 298 K gave suitable orange crystals (2 and 3), while dark red crystals of complex 4 were obtained at 273 K. The coordination geometry around the copper ion in 2 and 3 is distorted tetrahedron formed by two N atoms from the Schiff base ligand and two iodine substituents. The CuIN2I2 tetrahedra share iodine atoms which therefore double-bridge the neighboring copper(I) ions.

Scheme 17.

168 Current Trends in X-Ray Crystallography

**N**

**R2**

**R1**

**N S**

**S S**

**N N**

**Cu**

**R2**

**R2**

**R1**

**R1**

**R2**

**N N N N Cu Cu**

**Cu <sup>S</sup> <sup>N</sup>**

**Cu**

**R1**

**Cu N**

I II III

**R2 Cu**

**R1**

**R1**

IV VI

**N N**

VII VIII

as a bidentate ligand coordinating *via* two N atoms to the copper.

**4.1 Copper(I) complexes with symmetric bidentate Schiff base ligand** 

**R2**

The reaction of equimolar amounts of Meca2en (L15) at the presence of copper(I) iodide in acetonitrile at room temperature yielded yellow microcrystalline powder of mononuclear copper(I) complex Cu(Meca2en)(CH3CN)I (1) (Scheme 16) [56]. Slow evaporation of the solvent, 1:1 *v/v* chloroform:acetonitrile, at 273 K gave suitable yellow crystals. The coordination geometry around the copper ion is distorted tetrahedron formed by two N atoms from Meca2en, one N atom from acetonitrile and one iodine atom. The Meca2en acts

**N N**

**Cu**

**CH H3C <sup>3</sup>**

**CH3CN I**

**R1**

**Cu**

**Cu N N**

**N N**

**N N**

**Cu**

**R2 R2**

**N**

**N**

**Cu**

**4.1.1 Copper(I) iodide complexes** 

**R1**

**R2 R2**

**R1**

**R1**

Scheme 15.

Scheme 16.

However, the chelate N-Cu-N angle in 2 (100.17(12)°) is larger than the corresponding angle in 3 (82.7(3)°), while the I-Cu-I angle in 2 (104.517(17)°) is larger thanthe corresponding one in 3 (119.65(4)°), making the distortion of the tetrahedron considerably larger in (3) because of restricting bite angle of the chelating ligand. The N-Cu-I bond angles range from 100.53(9) to 122.48(9)° in 2 are similar to the corresponding angle in 3 (103.8(2) – 121.8(2)°). The bond distances Cu-I (2.7264(6) Å) and Cu-N (2.055(3) and 2.065(3) Å) in 2 are similar to the corresponding bond distances in 3 (2.6903(14), 2.069(7) and 2.085(7) Å, respectively). The dinuclear unit in these complexes is centrosymmetric with crystallographic center of symmetry located between the two copper(I) ion. The distances between the two copper(I) ions are 3.372(2) Å in 2 and 2.635(2) Å in 3.

The reaction of equimolar amounts of bz2en (L7), phca2en (L14) and Phca2-dab (L17) at the presence of copper(I) iodide in acetonitrile at room temperature yielded mononuclear copper(I) complexes [Cu(bz2en)][Cu2I4] (6) [47], [Cu(Phca2en)2][I3-] (6) [54] and [Cu(Phca2 dab)2][[CuI2] (7) [61] (Scheme 18). Slow diffusion of diethylether vapour into the concentrated acetonitrile-dichloromethane solution for 5, acetonitrile solution for 6 and chloroform solution for 7 at 298 K gave suitable dark red crystals.

The Schiff base ligand Phca2-dab (L17) have two different phenyl rings (the inner and outer phenyl rings) [61]. They play different role in the arrangement of the cations and anions of [Cu(Phca2-dab)2][CuI] (7). As a result, a one-dimensional net of 7 molecules is generated by 4-PE (fourfold phenyl embrace) including Ri rings (Fig. 1a). The Ro rings are not involved in the 4-PE local interactions. The [CuI2]- anions in the crystal structure are located in the space between Ro rings of the two adjacent cations (Fig. 1b) [61].

Structural Diversity on Copper(I) Schiff Base Complexes 171

**Cu**

The copper(I) atom in 8 is coordinated by two iodine ions and one nitrogen atom from Schiff-base ligand in distorted trigonal planar coordination geometry. In the crystal structure of 8 the (3,4,5-MeO-ba)2bn acts as a bridging ligand with the nitrogen atoms of the two imine functions. This leads to formation of dinuclear [Cu2(μ-(3,4,5-MeO-ba)2bn)] groups which are bridged by two iodine anions [(μ-I)2] into a neutral 1D-chain copper(I) iodide

Fig. 2. D-chain of complex 8 running along the [001] direction. Symmetry codes: (a) -x+1,-y,-

The Cu-N distance 1.9733(19) Ǻ is similar like in other copper(I) complexes [41,43]. The Cu-I distances of 2.5491(4) and 2.5648(3) Ǻ are slightly shorter than those of 2.6650(5) and 2.7393(5) Ǻ in the 1D-chain copper(I) complex [Cu2(μ-I)2(PPh3)2(4,4'-bpy)]n [73]. The Cu···Cu distance in the Cu-(*μ*-I)2-Cu fragment of 2 is 2.5583(6) Ǻ, i.e. shorter than in other similar Cu-

**I I**

**Cu**

**<sup>N</sup> <sup>N</sup>**

**OMe**

**Cu**

**MeO**

**MeO**

**MeO**

**MeO**

Scheme 19.

coordination polymer (Fig. 2).

z+1; (b) -x+1,-y,-z+2

(μ-I)2-Cu complexes [73].

**OMe**

**I I**

**Cu**

**OMe**

**OMe**

**n**

**OMe**

**OMe**

**OMe**

**<sup>N</sup> <sup>N</sup>**

**OMe**

Scheme 18.

The solid-state structure of complexes 5-7 reveals ionic complexes containing a cation of copper(I) ion coordinated to four nitrogen atoms of two Schiff base ligands. The coordination geometry around the copper ion is distorted tetrahedron. The complexes contain anions di-μ-iodo-diiododicuprate(I) for 5, diiodocuprate(I) for 6 and I3 for 7.

While a tetrahedral geometry might be expected for copper(I) complexes 6 and 7, the coordination sphere around copper(I) in these complexes is distorted by the restricting bite angle of the chelating Schiff base ligand. The average Cu-N bond distance of 2.023 Å in 6 is similar to the corresponding bond distance in 7 (2.035 Å). The chelate N-Cu-N angle in 6 (83.67(11)°) is shorter than similar to the corresponding bond angle in 7 (102.59(15)°).

Fig. 1. a) One-dimensional net of fourfold phenyl embrace (4-PE) in 7. b) Representation of anions (CuI2) associated with phenyl rings Ro.

The reaction of equimolar amounts of (3,4,5-MeO-ba)2bn (L43) in the presences of copper(I) iodide yields polymeric copper(I) chain complex [Cu2(μ-(3,4,5-MeO-ba)2bn)(μ-I)2]n (8) (Scheme 19) [33]. Slow evaporation of the solvent at 273 K gave suitable yellow crystals.

#### Scheme 19.

170 Current Trends in X-Ray Crystallography

**N N**

The solid-state structure of complexes 5-7 reveals ionic complexes containing a cation of copper(I) ion coordinated to four nitrogen atoms of two Schiff base ligands. The coordination geometry around the copper ion is distorted tetrahedron. The complexes contain anions di-μ-iodo-diiododicuprate(I) for 5, diiodocuprate(I) for 6 and I3-

While a tetrahedral geometry might be expected for copper(I) complexes 6 and 7, the coordination sphere around copper(I) in these complexes is distorted by the restricting bite angle of the chelating Schiff base ligand. The average Cu-N bond distance of 2.023 Å in 6 is similar to the corresponding bond distance in 7 (2.035 Å). The chelate N-Cu-N angle in 6 (83.67(11)°) is shorter than similar to the corresponding bond angle in 7

**N**

**N**

**Cu CuI2**

**N N**

**N**

**Cu CuI2**

**N**

**Cu Cu2I**

**4**

**N**

5 6 7

a b

anions (CuI2) associated with phenyl rings Ro.

Fig. 1. a) One-dimensional net of fourfold phenyl embrace (4-PE) in 7. b) Representation of

The reaction of equimolar amounts of (3,4,5-MeO-ba)2bn (L43) in the presences of copper(I) iodide yields polymeric copper(I) chain complex [Cu2(μ-(3,4,5-MeO-ba)2bn)(μ-I)2]n (8) (Scheme 19) [33]. Slow evaporation of the solvent at 273 K gave suitable yellow

**N N**

**N**

Scheme 18.

for 7.

(102.59(15)°).

crystals.

The copper(I) atom in 8 is coordinated by two iodine ions and one nitrogen atom from Schiff-base ligand in distorted trigonal planar coordination geometry. In the crystal structure of 8 the (3,4,5-MeO-ba)2bn acts as a bridging ligand with the nitrogen atoms of the two imine functions. This leads to formation of dinuclear [Cu2(μ-(3,4,5-MeO-ba)2bn)] groups which are bridged by two iodine anions [(μ-I)2] into a neutral 1D-chain copper(I) iodide coordination polymer (Fig. 2).

Fig. 2. D-chain of complex 8 running along the [001] direction. Symmetry codes: (a) -x+1,-y, z+1; (b) -x+1,-y,-z+2

The Cu-N distance 1.9733(19) Ǻ is similar like in other copper(I) complexes [41,43]. The Cu-I distances of 2.5491(4) and 2.5648(3) Ǻ are slightly shorter than those of 2.6650(5) and 2.7393(5) Ǻ in the 1D-chain copper(I) complex [Cu2(μ-I)2(PPh3)2(4,4'-bpy)]n [73]. The Cu···Cu distance in the Cu-(*μ*-I)2-Cu fragment of 2 is 2.5583(6) Ǻ, i.e. shorter than in other similar Cu- (μ-I)2-Cu complexes [73].

Structural Diversity on Copper(I) Schiff Base Complexes 173

The pseudohalide NCS- is known to coordinate to metal ions in both terminal and bridging modes [76,77]. Thiocyanate ion can afford a variety of coordination bridging modes (Scheme 21), such as μ-1,3-NCS, μ-1,1-NCS, μ-1,1-SCN, μ-1,1,3-NCS and μ-1,1,3-SCN, and link one or more transition metal ions to form zero, one-, two- and three-dimensional complexes [76,77].

The reaction of bidentate Schiff base ligand (3-Me-ba)2en (L1), (3,4,5-Meo-ba)2en (L2) and (2- MeO-ba)2en (L3) with CuSCN in an acetonitrile, three copper(I) thiocyanate coordination polymers, [Cu((3-Me-ba)2en)(SCN)]n (11), [Cu((3,4,5-MeO-ba)2en)(SCN)]n (12) and [Cu((2- MeO-ba)2en)(SCN)]n (13), with one-dimensional coordination polymer chains (Scheme 22), have been prepared [41,43]. Slow evaporation of the solvent at 273 K gave suitable yellow

**N**

**\***

**n**

**N**

**Cu**

**R1**

**R1**

**R2**

R1 = R3 = H, R2 = CH3 (11) R1 = R2 = R3 = CH3O (12) R2 = R3 = H, R1 = CH3O (13)

**R3**

**SCN**

**Cu**

**R3**

**R2**

**4.1.2 Copper(I) thiocyanate complexes** 

Scheme 21.

crystals of 11-13.

Scheme 22.

The reaction of dinuclear copper(I) complex [Cu(ca2en)(I)]2 (3) [51] or mononuclear copper(I) complex [Cu(Phca2en)2][I3-] (6) [54] with PPh3 in an acetonitrile solution mononuclear copper(I) complex [Cu(ca2en)(PPh3)I] (9) [52] and [Cu(Phca2en)(PPh3)I] (10) [55] have been prepared (Scheme 20). Slow diffusion of diethylether vapour into the concentrated acetonitrile solution for 9 and 10 at 298 K gave suitable orange crystals.

Scheme 20.

The copper(I) ion in 9 and 10 is coordinated to two N atoms of one Schiff base ligand, one P from PPh3 and one iodine group in geometry distorted by the restricting bite angle of the chelating ligands. The chelate N-Cu-N angle (81.33(7)°) in 9 is similar to the corresponding bond distance and angle in 10 (2.104 Å and 81.74(5)°). The P-Cu-I angle is 120.964(15) and 115.582(11)° in 9 and 10, respectively, being larger than the tetrahedral values. The Cu-N (2.0915(17), 2.0918(17) Å), Cu-I (2.6469(4) Å) and Cu-P (2.2327(6) Å) bond distances in 9 agree well with the corresponding distances in 10 (2.1129(11), 2.0961(12), 2.6501(2) and 2.2342(4) Å, respectively).

Compounds containing M-PPh3 moieties are recognized to form multiple phenyl embrance (MPE) as predominant supramolecular motifs [74,75]. In the complex 10, phenyl rings of PPh3 groups exhibit different conformations that are illustrated in Fig. 3. The Cu-PPh3 moiety of roughly threefold symmetry forms dimers that are separated from each other 7.270(7) Å, with Cu-PP angle of 173.61(1)° [55].

Fig. 3. Conformation of phenyl rings for Cu-PPh3 moiety viewed along P-M in 10.

#### **4.1.2 Copper(I) thiocyanate complexes**

The pseudohalide NCS- is known to coordinate to metal ions in both terminal and bridging modes [76,77]. Thiocyanate ion can afford a variety of coordination bridging modes (Scheme 21), such as μ-1,3-NCS, μ-1,1-NCS, μ-1,1-SCN, μ-1,1,3-NCS and μ-1,1,3-SCN, and link one or more transition metal ions to form zero, one-, two- and three-dimensional complexes [76,77].

Scheme 21.

172 Current Trends in X-Ray Crystallography

The reaction of dinuclear copper(I) complex [Cu(ca2en)(I)]2 (3) [51] or mononuclear copper(I) complex [Cu(Phca2en)2][I3-] (6) [54] with PPh3 in an acetonitrile solution mononuclear copper(I) complex [Cu(ca2en)(PPh3)I] (9) [52] and [Cu(Phca2en)(PPh3)I] (10) [55] have been prepared (Scheme 20). Slow diffusion of diethylether vapour into the concentrated

**N N**

**R R**

**Cu**

The copper(I) ion in 9 and 10 is coordinated to two N atoms of one Schiff base ligand, one P from PPh3 and one iodine group in geometry distorted by the restricting bite angle of the chelating ligands. The chelate N-Cu-N angle (81.33(7)°) in 9 is similar to the corresponding bond distance and angle in 10 (2.104 Å and 81.74(5)°). The P-Cu-I angle is 120.964(15) and 115.582(11)° in 9 and 10, respectively, being larger than the tetrahedral values. The Cu-N (2.0915(17), 2.0918(17) Å), Cu-I (2.6469(4) Å) and Cu-P (2.2327(6) Å) bond distances in 9 agree well with the corresponding distances in 10 (2.1129(11), 2.0961(12), 2.6501(2) and

Compounds containing M-PPh3 moieties are recognized to form multiple phenyl embrance (MPE) as predominant supramolecular motifs [74,75]. In the complex 10, phenyl rings of PPh3 groups exhibit different conformations that are illustrated in Fig. 3. The Cu-PPh3 moiety of roughly threefold symmetry forms dimers that are separated from each other

Fig. 3. Conformation of phenyl rings for Cu-PPh3 moiety viewed along P-M in 10.

**I PPh3**

acetonitrile solution for 9 and 10 at 298 K gave suitable orange crystals.

R = H (9) R = Ph (10)

Scheme 20.

2.2342(4) Å, respectively).

7.270(7) Å, with Cu-PP angle of 173.61(1)° [55].

The reaction of bidentate Schiff base ligand (3-Me-ba)2en (L1), (3,4,5-Meo-ba)2en (L2) and (2- MeO-ba)2en (L3) with CuSCN in an acetonitrile, three copper(I) thiocyanate coordination polymers, [Cu((3-Me-ba)2en)(SCN)]n (11), [Cu((3,4,5-MeO-ba)2en)(SCN)]n (12) and [Cu((2- MeO-ba)2en)(SCN)]n (13), with one-dimensional coordination polymer chains (Scheme 22), have been prepared [41,43]. Slow evaporation of the solvent at 273 K gave suitable yellow crystals of 11-13.

Scheme 22.

Structural Diversity on Copper(I) Schiff Base Complexes 175

**R**

**ClO4**

**N N**

**R R**

R = H (13) R = Ph (14)

The average bite angle of the ligand (N-Cu-N) in both complexes is 85.3° [46]. In 13, the average Cu-N bond length is 2.073 Å, with an average dihedral angle of 73.1° between the two CuN2 coordination planes, while the Cu-N bond lengths in 14 are in range from 2.014(4) to 2.183(4) Å, with dihedral angle of 63.9(2)° [46]. Complex 13 shows a quasireversible CuII/I couple in cyclic voltametery with an E1/2 of 0.81 V *vs* SCE, while this couple is much more reversible in complex 14 with an E1/2 of 0.66 V *vs* SCE [46]. Interestingly, the emission spectrum of complex 14 shows an additionalband around 550 nm in methanol albeit very weak which is absent in dichloromethane. Both the emissions in 14 in methanol originate

In recent years, Dehghanpour *et al*. have systematically studied on copper(I) complexes of the type [Cu(NN)2]+ or [Cu(NN)(P)2]+ with unconjugated Schiff base ligands [44,48,53,57,59,62]. For example, the reaction of nca2en (L13) in the presences of [Cu(CH3CN)4]ClO4 (2:1 molar ratio) in acetonitrile, yielded orange-red precipitates of [Cu(nca2en)2]ClO4 (15) (Scheme 25). Single crystals of 15, were grown by slow diffusion of Et2O into a concentrated acetonitrile solution of the complex [53]. Complex 15 shows a

The solid-state structures of complexes 15-17 (Scheme 25) reveal copper(I) ion coordinated to four N atoms of two Schiff base ligands. The coordination geometry around the copper ion is distorted by the restricting bite angle of the chelating ligands. The chelate N-Cu-N angle (84.2(2)°) in 15 is similar to the corresponding bond angle in 16 (82.27(5) and 82.29(9)°) and is shorter than the corresponding bond angle in 17 (99.3(18) and 100.7(18)°). The Cu-N (2.044(3) and 2.020(3) Å) bond distances in 15 agree well with the same distances in 16 (2.035(2),

The structure of Schiff base ligands L2 and L11, are very similarto the ligands reported previously, but the side substitutes are changed to more bulky groups (3 methoxy groups in L2 and one anthryl group in L11), which is hence expected to exhibit unusual coordination mode with copper(I) ion. The reaction of L2 in the presence of [Cu(CH3CN)4]ClO4 (2:1 molar ratio) in acetonitrile, yielded yellow precipitate of [Cu((3,4,5-MeO-ba)2en)(CH3CN)2]ClO4 (18) (Scheme 26). Single crystals of 18 were grown by slow diffusion of Et2O into an acetonitrile solution of the complex [42]. The copper(I) ion is coordinated by two N atoms from one bidentate Schiff base ligand and two N atoms from two acetonitrile groups. The

quasireversible CuII/I couple in cyclic voltametery with an E1/2 of 0.55 V *vs* SCE.

2.046(2), 2.062(2) and 2.038(2) Å) and in 17 (2.019(4), 2.022(4), 2.041(5) and 2.046(4) Å).

**N N**

**R**

Scheme 24.

from the MLCT state [46].

**Cu**

The crystal structures of these complexes have common features. In these complexes distorted tetrahedral coordination at Cu(I) is defined by the two N donor atoms of the Schiff base ligands and the N and S donor atoms of two thiocyanate ligands (Scheme 23). The Schiff base ligands act as chelating ligands while the SCN- anion acts as a bridging ligand.

In 12, the Cu…Cu separation through the bridging thiocyanate ligand is 5.604 Å. The Cu-S bond length 2.3468(7) Å is greater compared with those of the Cu-N bonds (mean distance 2.06 Å), which causes a significant distortion of the coordination polyhedron around the Cu(I) ion. The values observed for Cu-N and Cu-S distances are comparable with those found in other tetrahedral Cu(I) complexes. Moreover, the Cu-N bond to the bridging SCN group is shorter than Cu-N bonds to the Schiff base ligands. The bridging SCN anion is almost linear with S-C-N bond angle of 179.4(2)o.

#### **4.1.3 Copper(I) perchlorate complexes**

CuIN4 chromophores which exhibit photoluminiscence in solution are known only in copper(I) complexes of substituted 1,10-phenanthrolines and Schiff bases. Many advances in the chemistry of copper(I) complexes have been achieved on four coordinated tetrahedral complexes of the type [Cu(NN)2]+ or [Cu(NN)(P)2]+ (Scheme 23), where NN is Schiff base ligand and P is triphenylphosphine [78-80]. These complexes have relatively stable framework and exhibit metal-to-ligand charge transfer transition in the visible region.

The reaction of L6 and L7 in the presences of [Cu(CH3CN)4]ClO4 (2:1 molar ratio) in degassed methanol under dry N2 atmosphere, yielded yellow and red precipitates of [Cu(ba2en)2]ClO4 (13) and [Cu(bz2en)2]ClO4 (14), respectively (Scheme 24). Single crystals of 13 and 14, were grown by slow diffusion of n-hexane into a dilute dichloromethane solution of the complexes [46].

Scheme 23.

Scheme 24.

174 Current Trends in X-Ray Crystallography

The crystal structures of these complexes have common features. In these complexes distorted tetrahedral coordination at Cu(I) is defined by the two N donor atoms of the Schiff base ligands and the N and S donor atoms of two thiocyanate ligands (Scheme 23). The Schiff base ligands act as chelating ligands while the SCN- anion acts as a bridging

In 12, the Cu…Cu separation through the bridging thiocyanate ligand is 5.604 Å. The Cu-S bond length 2.3468(7) Å is greater compared with those of the Cu-N bonds (mean distance 2.06 Å), which causes a significant distortion of the coordination polyhedron around the Cu(I) ion. The values observed for Cu-N and Cu-S distances are comparable with those found in other tetrahedral Cu(I) complexes. Moreover, the Cu-N bond to the bridging SCN group is shorter than Cu-N bonds to the Schiff base ligands. The bridging SCN anion is

CuIN4 chromophores which exhibit photoluminiscence in solution are known only in copper(I) complexes of substituted 1,10-phenanthrolines and Schiff bases. Many advances in the chemistry of copper(I) complexes have been achieved on four coordinated tetrahedral complexes of the type [Cu(NN)2]+ or [Cu(NN)(P)2]+ (Scheme 23), where NN is Schiff base ligand and P is triphenylphosphine [78-80]. These complexes have relatively stable framework and exhibit metal-to-ligand charge transfer transition in the visible

The reaction of L6 and L7 in the presences of [Cu(CH3CN)4]ClO4 (2:1 molar ratio) in degassed methanol under dry N2 atmosphere, yielded yellow and red precipitates of [Cu(ba2en)2]ClO4 (13) and [Cu(bz2en)2]ClO4 (14), respectively (Scheme 24). Single crystals of 13 and 14, were grown by slow diffusion of n-hexane into a dilute dichloromethane solution of the

**ClO4**

**N N Schiff base ligand**

ligand.

region.

complexes [46].

Scheme 23.

almost linear with S-C-N bond angle of 179.4(2)o.

**Cu**

**N N**

**N N**

**4.1.3 Copper(I) perchlorate complexes** 

The average bite angle of the ligand (N-Cu-N) in both complexes is 85.3° [46]. In 13, the average Cu-N bond length is 2.073 Å, with an average dihedral angle of 73.1° between the two CuN2 coordination planes, while the Cu-N bond lengths in 14 are in range from 2.014(4) to 2.183(4) Å, with dihedral angle of 63.9(2)° [46]. Complex 13 shows a quasireversible CuII/I couple in cyclic voltametery with an E1/2 of 0.81 V *vs* SCE, while this couple is much more reversible in complex 14 with an E1/2 of 0.66 V *vs* SCE [46]. Interestingly, the emission spectrum of complex 14 shows an additionalband around 550 nm in methanol albeit very weak which is absent in dichloromethane. Both the emissions in 14 in methanol originate from the MLCT state [46].

In recent years, Dehghanpour *et al*. have systematically studied on copper(I) complexes of the type [Cu(NN)2]+ or [Cu(NN)(P)2]+ with unconjugated Schiff base ligands [44,48,53,57,59,62]. For example, the reaction of nca2en (L13) in the presences of [Cu(CH3CN)4]ClO4 (2:1 molar ratio) in acetonitrile, yielded orange-red precipitates of [Cu(nca2en)2]ClO4 (15) (Scheme 25). Single crystals of 15, were grown by slow diffusion of Et2O into a concentrated acetonitrile solution of the complex [53]. Complex 15 shows a quasireversible CuII/I couple in cyclic voltametery with an E1/2 of 0.55 V *vs* SCE.

The solid-state structures of complexes 15-17 (Scheme 25) reveal copper(I) ion coordinated to four N atoms of two Schiff base ligands. The coordination geometry around the copper ion is distorted by the restricting bite angle of the chelating ligands. The chelate N-Cu-N angle (84.2(2)°) in 15 is similar to the corresponding bond angle in 16 (82.27(5) and 82.29(9)°) and is shorter than the corresponding bond angle in 17 (99.3(18) and 100.7(18)°). The Cu-N (2.044(3) and 2.020(3) Å) bond distances in 15 agree well with the same distances in 16 (2.035(2), 2.046(2), 2.062(2) and 2.038(2) Å) and in 17 (2.019(4), 2.022(4), 2.041(5) and 2.046(4) Å).

The structure of Schiff base ligands L2 and L11, are very similarto the ligands reported previously, but the side substitutes are changed to more bulky groups (3 methoxy groups in L2 and one anthryl group in L11), which is hence expected to exhibit unusual coordination mode with copper(I) ion. The reaction of L2 in the presence of [Cu(CH3CN)4]ClO4 (2:1 molar ratio) in acetonitrile, yielded yellow precipitate of [Cu((3,4,5-MeO-ba)2en)(CH3CN)2]ClO4 (18) (Scheme 26). Single crystals of 18 were grown by slow diffusion of Et2O into an acetonitrile solution of the complex [42]. The copper(I) ion is coordinated by two N atoms from one bidentate Schiff base ligand and two N atoms from two acetonitrile groups. The

Structural Diversity on Copper(I) Schiff Base Complexes 177

Fig. 4. An ORTEP view of 19, showing the atomic numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. H atoms have been omitted for clarity.

**4.2 Copper(I) complexes with asymmetric bidentate Schiff base ligand** 

resulting in more stable three-coordinated conformation.

into a concentrated acetonitrile solution of the complex.

**O N N**

**Cu N N O**

L51 [60] 20 21

**N N**

Scheme 27.

Apparently, the coordination pattern of 19 is very different from the copper(I) complexes reported so far [46,47]. In this complex, the bulky anthryl group has larger steric hindrance and may inhibit another imine-N of the second ligand to coordinated with copper(I),

In recent years, Dehghanpour *et al*. have systematically studied on copper(I) complexes of the type [Cu(NN)2]+ or [Cu(NN)(P)2]+ with asymmetric Schiff base ligands [60, 63-65]. For example, the reaction of 4-ampc (L26) (Scheme 9) and dpa-qa (L51) (Scheme 27) in the presences of [Cu(CH3CN)4]BPh4 (2:1 molar ratio) in acetonitrile, yielded orange and darkred precipitates of [Cu(4-ampc)2]BPh4 (20) [64] (Scheme 27) and [Cu(dpa-qa)2]BPh4 (21) [60] (Scheme 27), respectively. Single crystals of 20 and 21, were grown by slow diffusion of Et2O

**BPh4**

**N N Cu N N**

**BPh4**

copper atom adopts a tetrahedral geometry. The Cu-N(ligand) distances are 2.076(3) and 2.076(3) Å, and the Cu-N(acetonitrile) distances are 1.964(4) and 1.975(4) Å.

Scheme 25.

The reaction of L11, at the presence of [Cu(CH3CN)4]BF4 (2:1 molar ratio) in methanol, gave yellow-green precipitates of [Cu(Anca2en)2]BF4 (19) (Fig. 4) [50]. Single crystals suitable for X-ray diffraction analysis were grown from a dichloromethane-ethanol (*v/v*, 1/1) solution of complex. The structure of 19 is shown in Fig. 23. In 19 the copper(I) ion is coordinated to three N atoms from two bidentate Schiff base ligands in a distorted trigonal planar geometry. The remaining imine N atom remains uncoordinated. The Cu-N distances are 2.111(3), 1.946(4) and 1.930(3) Å, respectively.

R = -CH2-CH2- (15) R = -Ph- (16) R = -Ph-Ph- (17)

Scheme 26.

copper atom adopts a tetrahedral geometry. The Cu-N(ligand) distances are 2.076(3) and

**Cu**

**ClO4**

**N N O2N NO2**

R

Scheme 25.

Scheme 26.

2.111(3), 1.946(4) and 1.930(3) Å, respectively.

R = -CH2-CH2- (15) R = -Ph- (16) R = -Ph-Ph- (17)

The reaction of L11, at the presence of [Cu(CH3CN)4]BF4 (2:1 molar ratio) in methanol, gave yellow-green precipitates of [Cu(Anca2en)2]BF4 (19) (Fig. 4) [50]. Single crystals suitable for X-ray diffraction analysis were grown from a dichloromethane-ethanol (*v/v*, 1/1) solution of complex. The structure of 19 is shown in Fig. 23. In 19 the copper(I) ion is coordinated to three N atoms from two bidentate Schiff base ligands in a distorted trigonal planar geometry. The remaining imine N atom remains uncoordinated. The Cu-N distances are

**Cu**

**MeO ClO4**

**MeO OMe MeO OMe**

**OMe**

**CH3CN NCCH3**

**N N**

**R N N O2N NO2**

2.076(3) Å, and the Cu-N(acetonitrile) distances are 1.964(4) and 1.975(4) Å.

Fig. 4. An ORTEP view of 19, showing the atomic numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. H atoms have been omitted for clarity.

Apparently, the coordination pattern of 19 is very different from the copper(I) complexes reported so far [46,47]. In this complex, the bulky anthryl group has larger steric hindrance and may inhibit another imine-N of the second ligand to coordinated with copper(I), resulting in more stable three-coordinated conformation.

#### **4.2 Copper(I) complexes with asymmetric bidentate Schiff base ligand**

In recent years, Dehghanpour *et al*. have systematically studied on copper(I) complexes of the type [Cu(NN)2]+ or [Cu(NN)(P)2]+ with asymmetric Schiff base ligands [60, 63-65]. For example, the reaction of 4-ampc (L26) (Scheme 9) and dpa-qa (L51) (Scheme 27) in the presences of [Cu(CH3CN)4]BPh4 (2:1 molar ratio) in acetonitrile, yielded orange and darkred precipitates of [Cu(4-ampc)2]BPh4 (20) [64] (Scheme 27) and [Cu(dpa-qa)2]BPh4 (21) [60] (Scheme 27), respectively. Single crystals of 20 and 21, were grown by slow diffusion of Et2O into a concentrated acetonitrile solution of the complex.

Scheme 27.

Structural Diversity on Copper(I) Schiff Base Complexes 179

**S**

**Cu**

**S**

**N O**

**Cu I**

**I**

**S S**

**N N Cu**

The asymmetric unit of complex 23 contains one copper atom, one NCS- ligand and a

ligand through its nitrogen atom, and ca2dapte acts as a tridentate ligand coordinated through one N-imino, and two sulfur atoms. The second imino arm is directed away of the copper(I) center. Copper(I) ion has a distorted tetrahedral coordination geometry formed by one nitrogen and two sulfur atom from the Schiff base ligand and one nitrogen from thiocyanate, with significantly different bond distances [Cu-N1 2.064(2), Cu-S1 2.2886(8), Cu-S2 2.3824(7) and Cu-N3 1.903(2) Å] [66]. The high distortion of the coordination tetrahedron is essentially due to the steric requirements of the ca2dapte bis-chelating ligand leading to strong deviation of the bond angles around the copper(I) ion from ideal tetrahedric values [N-Cu-S, N-Cu-N and S-Cu-S bond angles are in the range 86.2-130.0°]

In the mononuclear copper(I) complex [Cu(ca2dapte)(NCS)] (23), the N2S2 Schiff base ligand ca2dapte, acts as a tridentate ligand surrounding the copper(I) ion [66]. In [Cu2(ca2dapte)(PPh3)2X2] (X = I (24) and Br (25)) complexes [35], ca2dapte acts as two

**SCN**

**O N**

**Cu**

**S**

**S**

**N O Cu I**

**I**

**Cu**

**n**

pseudohalide anion acts as a terminal

**O N**

ca2dapte Schiff base ligand. In this complex, the NCS-

**I**

**I**

**Cu**

Scheme 28.

Scheme 29.

[66].

Since no d-d transitions are expected for a d10 complex, the UV-Vis bands are assigned to MLCT or ligand-centered π→π٭ transitions [60]. The absorption spectrum of 21, in CHCl3 reveals a band with a true maximum at 503 nm. This observation is in ag5reement with the higher conjugation in the coordinated dpa-qa [60]. Complex 20 shows a quasireversible CuII/I couple in cyclic voltametery with an E1/2 of 0.47 V *vs* SCE [60].

#### **4.3 Copper(I) complexes with symmetric tetradentate Schiff base ligands**

Flexible N/S or NN donor ligands have received much attention due to their use in constructing coordination frameworks by self-assembly, and also in investigating the mechanism of supramolecular interactions [81-86]. With flexible ligand, the competition between bridging and chelating coordination modes is an important factor in producing mono, di, and polynuclear metal complexes [81-86].

### **4.3.1 (NS)2 Schiff bases with a flexible spacer**

In recent years, Morshedi *et al*. have systematically studied on copper(I) complexes with flexible N/S donor Schiff base ligands [35,36,66]. The tetradentate (NS)2 Schiff bases L31 and L32 were prepared as reported elsewhere [35,36,66]. The reaction of (thio)2dapte (L32) in the presences of CuI (1:1 molar ratio) in acetonitrile, yielded dark-red precipitates of new onedimensional copper(I) coordination polymer [Cu2(μ-I)2(μ-(thio)2dapte)]n (22) (Scheme 28). Single crystals of 22 were grown by slow evaporation of solvent at room temperature for several days [36]. The solubility of 22 in common organic solvents is very low. Complex 22 crystallizes with the asymmetric unit formed by one copper(I) and one iodine ion located in general positions, and one centrosymmetric organic ligand (thio)2dapte placed in the inversion center (1/2, 1, 1/2). In this complex, the flexible Schiff base ligand (thio)2dapte acts as a bis-chelating ligand through its two iminic nitrogens and two sulfur atoms of ethanedithiolate group, creating the [Cu2(μ-(thio)2dapte)] dinuclear fragment. Such dinuclear entities are linked to each other by the two iodine anions acting as a doubly μ2 bridging ligand [(μ-I)2] and forming one-dimensional copper(I) coordination polymer with the general formula [Cu2(μ-I)2(μ-(thio)2dapte)]n (22). In this complex, copper(I) ion has a distorted tetrahedral coordination geometry formed by one nitrogen and one sulfur atom from the Schiff base ligand and two iodine substituents, with significantly different bond distances [Cu1-N1 2.073(4), Cu1-S1 2.342(2), Cu1-I1 2.6008(7) and Cu1-I1b 2.6575(7) Å]. The highly distorted tetrahedral geometry around the copper(I) ion is also due to the small bite angle of the (thio)2dapte bis-chelating ligand. The Cu1Cu1b distance of copper atoms connected through the bridging iodine ligands (2.6745(11) Å) is shorter than the corresponding distance of copper atoms connected through the bis-chelating ligand (Cu1Cu1a 6.942(1) Å).

By using the bis-chelating Schiff base ligand ca2dapte [35,66] and at the similar condition to 22, the reaction of ca2dapte (L31) in the presences of CuSCN (1:1 molar ratio) in acetonitrile under N2 yielded orange-red precipitates of mononuclear copper(I) complex [Cu(ca2dapte)(NCS)] (23) (Scheme 29). Single crystals of 23, were grown by slow diffusion of Et2O vapor into a concentrated solution of complex in acetonitrile at room temperature [66]. In the 1H-NMR spectra of 23, the iminic protons corresponding to the coordinated and non coordinated imine groups appear at 8.95 and 8.97 ppm, respectively (free ligand has 8.14 ppm).

Scheme 28.

178 Current Trends in X-Ray Crystallography

Since no d-d transitions are expected for a d10 complex, the UV-Vis bands are assigned to MLCT or ligand-centered π→π٭ transitions [60]. The absorption spectrum of 21, in CHCl3 reveals a band with a true maximum at 503 nm. This observation is in ag5reement with the higher conjugation in the coordinated dpa-qa [60]. Complex 20 shows a quasireversible

Flexible N/S or NN donor ligands have received much attention due to their use in constructing coordination frameworks by self-assembly, and also in investigating the mechanism of supramolecular interactions [81-86]. With flexible ligand, the competition between bridging and chelating coordination modes is an important factor in producing

In recent years, Morshedi *et al*. have systematically studied on copper(I) complexes with flexible N/S donor Schiff base ligands [35,36,66]. The tetradentate (NS)2 Schiff bases L31 and L32 were prepared as reported elsewhere [35,36,66]. The reaction of (thio)2dapte (L32) in the presences of CuI (1:1 molar ratio) in acetonitrile, yielded dark-red precipitates of new onedimensional copper(I) coordination polymer [Cu2(μ-I)2(μ-(thio)2dapte)]n (22) (Scheme 28). Single crystals of 22 were grown by slow evaporation of solvent at room temperature for several days [36]. The solubility of 22 in common organic solvents is very low. Complex 22 crystallizes with the asymmetric unit formed by one copper(I) and one iodine ion located in general positions, and one centrosymmetric organic ligand (thio)2dapte placed in the inversion center (1/2, 1, 1/2). In this complex, the flexible Schiff base ligand (thio)2dapte acts as a bis-chelating ligand through its two iminic nitrogens and two sulfur atoms of ethanedithiolate group, creating the [Cu2(μ-(thio)2dapte)] dinuclear fragment. Such dinuclear entities are linked to each other by the two iodine anions acting as a doubly μ2 bridging ligand [(μ-I)2] and forming one-dimensional copper(I) coordination polymer with the general formula [Cu2(μ-I)2(μ-(thio)2dapte)]n (22). In this complex, copper(I) ion has a distorted tetrahedral coordination geometry formed by one nitrogen and one sulfur atom from the Schiff base ligand and two iodine substituents, with significantly different bond distances [Cu1-N1 2.073(4), Cu1-S1 2.342(2), Cu1-I1 2.6008(7) and Cu1-I1b 2.6575(7) Å]. The highly distorted tetrahedral geometry around the copper(I) ion is also due to the small bite angle of the (thio)2dapte bis-chelating ligand. The Cu1Cu1b distance of copper atoms connected through the bridging iodine ligands (2.6745(11) Å) is shorter than the corresponding distance of copper atoms connected through the bis-chelating ligand

By using the bis-chelating Schiff base ligand ca2dapte [35,66] and at the similar condition to 22, the reaction of ca2dapte (L31) in the presences of CuSCN (1:1 molar ratio) in acetonitrile under N2 yielded orange-red precipitates of mononuclear copper(I) complex [Cu(ca2dapte)(NCS)] (23) (Scheme 29). Single crystals of 23, were grown by slow diffusion of Et2O vapor into a concentrated solution of complex in acetonitrile at room temperature [66]. In the 1H-NMR spectra of 23, the iminic protons corresponding to the coordinated and non coordinated imine groups appear at 8.95 and 8.97 ppm, respectively (free ligand

CuII/I couple in cyclic voltametery with an E1/2 of 0.47 V *vs* SCE [60].

mono, di, and polynuclear metal complexes [81-86].

**4.3.1 (NS)2 Schiff bases with a flexible spacer** 

(Cu1Cu1a 6.942(1) Å).

has 8.14 ppm).

**4.3 Copper(I) complexes with symmetric tetradentate Schiff base ligands** 

Scheme 29.

The asymmetric unit of complex 23 contains one copper atom, one NCS- ligand and a ca2dapte Schiff base ligand. In this complex, the NCS pseudohalide anion acts as a terminal ligand through its nitrogen atom, and ca2dapte acts as a tridentate ligand coordinated through one N-imino, and two sulfur atoms. The second imino arm is directed away of the copper(I) center. Copper(I) ion has a distorted tetrahedral coordination geometry formed by one nitrogen and two sulfur atom from the Schiff base ligand and one nitrogen from thiocyanate, with significantly different bond distances [Cu-N1 2.064(2), Cu-S1 2.2886(8), Cu-S2 2.3824(7) and Cu-N3 1.903(2) Å] [66]. The high distortion of the coordination tetrahedron is essentially due to the steric requirements of the ca2dapte bis-chelating ligand leading to strong deviation of the bond angles around the copper(I) ion from ideal tetrahedric values [N-Cu-S, N-Cu-N and S-Cu-S bond angles are in the range 86.2-130.0°] [66].

In the mononuclear copper(I) complex [Cu(ca2dapte)(NCS)] (23), the N2S2 Schiff base ligand ca2dapte, acts as a tridentate ligand surrounding the copper(I) ion [66]. In [Cu2(ca2dapte)(PPh3)2X2] (X = I (24) and Br (25)) complexes [35], ca2dapte acts as two

Structural Diversity on Copper(I) Schiff Base Complexes 181

then stirred for 10 min to give a clear dark-red solution. Single crystals of 26, were grown by slow diffusion of Et2O vapor into a concentrated solution of the complex [35]. There are four similar but independent complex units in the asymmetric unit of 26. In the absence of other coordinating ligands the ca2dapte acts as a tetradentate ligand. However, [Cu(ca2dapte)NCS] complex is formed in the presence of NCS [66] causing that the ca2dapte

The solid-state structure of complex 26 reveals copper(I) ion coordinated to two N atoms and two sulfur atoms of one Schiff base ligand. The central Cu(I) ion has the common irregular pseudo-tetrahedral geometry arising from the low intraligand N-Cu-S chelate angles 86.55(12) and 86.93(11)° and S-Cu-S chelate angle 93.11(5)°. In the 1H-NMR spectrum of 26, the iminic protons corresponding to the coordinated imine groups appear as a doublet

In this type of complexes, N-donor ligands are mainly focused on Schiff bases containing

Dinuclear copper(I) complexes were obtained when the ligands with the –C=N- group in *ortho*-position of pyridine ring were used in the synthesis. The reaction of P2en (L35) [30,38] or (Mepk)2en (L36) [39,69] in the presences of CuI and PPh3 (1:2:2 molar ratio) in acetonitrile, yielded dark-red or orange precipitates of dinuclear copper(I) complexes [Cu2I2(μ-P2en)(PPh3)2] (27) or [Cu2I2(μ-(Mepk)2en)(PPh3)2]2CH3CN (28). Single crystals of 27 and 28, were grown by slow evaporation of solvent at room temperature for several days [38, 69]. These complexes are centrosymmetric dimers with pairs of Cu(PPh3)I units bridged by P2en [38] and (Mepk)2en [69]. The solid-state structure of complexes 27 and 28 reveals copper(I) ion coordinated to two N atoms of one Schiff base ligand, one P from PPh3 and one iodine group (Scheme 31). The central Cu(I) ion has the common irregular pseudo-tetrahedral coordination geometry arising from the low intraligand N-Cu-N chelate angles 79.40(15)° in 27 and 78.86(10)° in 28. The P-Cu-I angle is 123.11(4) and 119.05(3)° in 27 and 28,

acts as a tridentate ligand leaving a free site for the NCS to coordinate.

at 8.23 ppm (free ligand has 8.14 ppm).

pyridine group (see L35 and L36).

**4.3.2 (NN')2 Schiff bases with a flexible spacer** 

respectively, being larger than the ideal tetrahedral values.

**N**

**R**

R = H (27) R = CH3 (28)

The reaction of (Mepk)2en (L36) in the presence of [Cu(CH3CN)4]ClO4 and PPh3 (1:2:4 molar ratio) in acetonitrile yielded yellow precipitates of dinuclear copper(I) complexes [Cu2(μ- (Mepk)2en)(PPh3)4](ClO4)22CHCl3 (29) [39]. Single crystals of 29, were grown by slow

**PPh3**

**N**

**R**

**Ph3P**

**Cu**

**N**

**I**

**Cu**

**N**

Scheme 31.

**I**

independent bidentate ligands connected by a flexible bridge (Scheme 30), and in [Cu(ca2dapte)]ClO4 (26) the ligand is tetradentate surrounding the copper(I) ion [35] (Scheme 30).

26

Scheme 30.

Dinuclear complexes 24 and 25 were prepared by a similar procedure [35]. To a solution of PPh3 in acetonitrile was added a solution of CuX (X = I (24) and Br (25)) in acetonitrile and the mixture was stirred at room temperature for about 10 min to give a clear solution. Then, the ligand ca2dapte was added and a clear orange-red solution was obtained. Single crystals of 24 and 25, were grown by slow diffusion of Et2O vapor into a concentrated solution of complex [35]. These complexes are centrosymmetric dimers with pairs of Cu(PPh3)X units bridged by ca2dapte. The solid-state structure of complexes 24 and 25 reveals copper(I) ion coordinated to one N atoms and one sulfur atom of one Schiff base ligand, one P from PPh3 and one halide group. The central Cu(I)/Cu(Br) ion has a common irregular pseudotetrahedral geometry arising from the low intraligand N-Cu-S chelate angles 80.72(8)° in 24 and 80.54(19)° in 25. The P-Cu-X angle is 126.17(3) and 121.41(7)° in 24 and 10, respectively, being larger than the tetrahedral values. In the 1H-NMR spectra of 23 and 24, the iminic protons corresponding to the coordinated imine groups appear as a doublet at 8.41 and 8.33 ppm, respectively (free ligand has 8.14 ppm).

To a solution of [Cu(CH3CN)]ClO4 in acetonitrile was added, with continuous stirring, a solution of ca2dapte (L31) in the minimum amount of chloroform at room temperature and

independent bidentate ligands connected by a flexible bridge (Scheme 30), and in [Cu(ca2dapte)]ClO4 (26) the ligand is tetradentate surrounding the copper(I) ion [35]

X = I (24) X = Br (25)

**N**

**ClO4**

**S S**

**Cu**

26

Dinuclear complexes 24 and 25 were prepared by a similar procedure [35]. To a solution of PPh3 in acetonitrile was added a solution of CuX (X = I (24) and Br (25)) in acetonitrile and the mixture was stirred at room temperature for about 10 min to give a clear solution. Then, the ligand ca2dapte was added and a clear orange-red solution was obtained. Single crystals of 24 and 25, were grown by slow diffusion of Et2O vapor into a concentrated solution of complex [35]. These complexes are centrosymmetric dimers with pairs of Cu(PPh3)X units bridged by ca2dapte. The solid-state structure of complexes 24 and 25 reveals copper(I) ion coordinated to one N atoms and one sulfur atom of one Schiff base ligand, one P from PPh3 and one halide group. The central Cu(I)/Cu(Br) ion has a common irregular pseudotetrahedral geometry arising from the low intraligand N-Cu-S chelate angles 80.72(8)° in 24 and 80.54(19)° in 25. The P-Cu-X angle is 126.17(3) and 121.41(7)° in 24 and 10, respectively, being larger than the tetrahedral values. In the 1H-NMR spectra of 23 and 24, the iminic protons corresponding to the coordinated imine groups appear as a doublet at 8.41 and 8.33

To a solution of [Cu(CH3CN)]ClO4 in acetonitrile was added, with continuous stirring, a solution of ca2dapte (L31) in the minimum amount of chloroform at room temperature and

**S N Cu Ph3P X**

**N S Cu X PPh3**

**N**

(Scheme 30).

Scheme 30.

ppm, respectively (free ligand has 8.14 ppm).

then stirred for 10 min to give a clear dark-red solution. Single crystals of 26, were grown by slow diffusion of Et2O vapor into a concentrated solution of the complex [35]. There are four similar but independent complex units in the asymmetric unit of 26. In the absence of other coordinating ligands the ca2dapte acts as a tetradentate ligand. However, [Cu(ca2dapte)NCS] complex is formed in the presence of NCS [66] causing that the ca2dapte acts as a tridentate ligand leaving a free site for the NCS to coordinate.

The solid-state structure of complex 26 reveals copper(I) ion coordinated to two N atoms and two sulfur atoms of one Schiff base ligand. The central Cu(I) ion has the common irregular pseudo-tetrahedral geometry arising from the low intraligand N-Cu-S chelate angles 86.55(12) and 86.93(11)° and S-Cu-S chelate angle 93.11(5)°. In the 1H-NMR spectrum of 26, the iminic protons corresponding to the coordinated imine groups appear as a doublet at 8.23 ppm (free ligand has 8.14 ppm).

#### **4.3.2 (NN')2 Schiff bases with a flexible spacer**

In this type of complexes, N-donor ligands are mainly focused on Schiff bases containing pyridine group (see L35 and L36).

Dinuclear copper(I) complexes were obtained when the ligands with the –C=N- group in *ortho*-position of pyridine ring were used in the synthesis. The reaction of P2en (L35) [30,38] or (Mepk)2en (L36) [39,69] in the presences of CuI and PPh3 (1:2:2 molar ratio) in acetonitrile, yielded dark-red or orange precipitates of dinuclear copper(I) complexes [Cu2I2(μ-P2en)(PPh3)2] (27) or [Cu2I2(μ-(Mepk)2en)(PPh3)2]2CH3CN (28). Single crystals of 27 and 28, were grown by slow evaporation of solvent at room temperature for several days [38, 69]. These complexes are centrosymmetric dimers with pairs of Cu(PPh3)I units bridged by P2en [38] and (Mepk)2en [69]. The solid-state structure of complexes 27 and 28 reveals copper(I) ion coordinated to two N atoms of one Schiff base ligand, one P from PPh3 and one iodine group (Scheme 31). The central Cu(I) ion has the common irregular pseudo-tetrahedral coordination geometry arising from the low intraligand N-Cu-N chelate angles 79.40(15)° in 27 and 78.86(10)° in 28. The P-Cu-I angle is 123.11(4) and 119.05(3)° in 27 and 28, respectively, being larger than the ideal tetrahedral values.

Scheme 31.

The reaction of (Mepk)2en (L36) in the presence of [Cu(CH3CN)4]ClO4 and PPh3 (1:2:4 molar ratio) in acetonitrile yielded yellow precipitates of dinuclear copper(I) complexes [Cu2(μ- (Mepk)2en)(PPh3)4](ClO4)22CHCl3 (29) [39]. Single crystals of 29, were grown by slow

Structural Diversity on Copper(I) Schiff Base Complexes 183

The cation has a crystallographic *C*2 axis. This complex displays a quasireversible CuII/I

Though 30 does not show any emission in methanol at room temperature, at 77 K in methanol glass it displays two very distinct emission bands at 470 and 495 nm together with a faint one at 545 nm. It should be noted that in the rigid matrix at 77 K, methanol

In recent years, grid complexes have been targeted by many researchers as a template to arrange two bidentate ligand binding pockets orthogonal to each other. Brooker *et al*. systematically studied on grid complexes of first transition metal ions that exhibit interesting structural, electrochemical and magnetic properties [31,32, 87-90]. The flat bisbidentate ligand dppn [3,6-bis(2-pyridiyl)pyridazine] has been used for preparation of copper(I) gridlike complexes in 1992 (Scheme 34) [91]. In recent years, the incorporation of such grid-forming bis-bidentate Schiff base ligands into dppn has been explored (Scheme 13). They have been prepared from the reaction of 3,6-diformylpyridazine and substituted amino-benzenes. It was suggested that these ligands are preorganised to form a tetranuclear [2 × 2] grid complexes with a tetrahedrally coordinated metal ion such as copper(I) and

For preparation of grid copper(I) complexes, the bis-bidentate Schiff base ligands (Scheme 25) were suspended in pure dry acetone and degassed with nitrogen for 15 min. An equimolar amount of tetrakis(acetonitrile)copper(I) hexaflurophosphate was added and the reaction mixture refluxed under nitrogen for 2h. The diffusion of Et2O vapour into an acetone solution yielded single crystals of gridelike copper(I) complexes [Cu4(L45)4](PF6)4 (31) and [Cu4(L41)4](PF6)4 (32) (Fig. 5), while the layering of an acetone solution of the

While the tetranuclear cations [Cu4(L45)4](PF6)4 and [Cu4(L41)4](PF6)4 has no crystallographic imposed symmetry, the cation [Cu4(L45)4](PF6)4 contains a two-fold rotation axis relating two halves of the grid from the two ligand strands and two copper(I) ions (Fig. 42). In all of the [2 × 2] copper(I) grid complexes, the coordination geometry of the copper(I) centers is a

complex on benzene gave single crystals of [Cu4(L42)4](PF6)4 (33) (Fig. 5) [32].

couple with a half-wave potential of 0.12 V *vs*. SCE [37].

**4.4 Copper(I) grid complexes** 

silver(I) [32].

Scheme 34.

coordination to the copper(II) center in the excited state is not operative.

diffusion of Et2O into the concentrated solution at 273 K for several days [39]. These complexes are centrosymmetric dimers with pairs of Cu(PPh3)2 units bridged (Mepk)2en. The solid-state structure of complex 29 reveals copper(I) ion coordinated to two N atoms of one Schiff base ligand and two P from two PPh3 (Scheme 32). The central Cu(I) ion has the common irregular pseudo-tetrahedral geometry arising from the low intraligands N-Cu-N chelate angles 79.4(2)° and the P-Cu-P angle is 118.24(7)°. The N-Cu-P bond angles range from 111 to 120°, i.e. slightly more than in a regular tetrahedron (109.5°). The P-Cu-P angle has opened up due to the steric effect from the bulky PPh3 ligands. The CuCu' separation distance 7.06(1) Å in 29 is longer than that observed in 27 (6.2577(6) Å) which is also caused by steric effect of PPh3 ligand and also ClO4 anions.

Scheme 32.

Scheme 33.

The ligand L38 is a 2:1 condensate of benzaldehyde and triethylenetetramine (trien). The reaction of ba2trien in the presences of [Cu(CH3CN)4]ClO4 (1:1 molar ratio) in degassed methanol under N2 atmosphere yielded reddish yellow precipitates of mononuclear copper(I) complexe [Cu(ba2trien)]ClO4 (30) [37] (Scheme 33). Single crystals of 30, were grown by slow evaporation of dichloromethane-hexane mixture. The N4 coordination sphere of the copper(I) ion is significantly distorted from tetrahedral due to the steric constraints of the ligand with the Cu-Nimino bond lengths shorter than the Cu-Namino ones. The cation has a crystallographic *C*2 axis. This complex displays a quasireversible CuII/I couple with a half-wave potential of 0.12 V *vs*. SCE [37].

Though 30 does not show any emission in methanol at room temperature, at 77 K in methanol glass it displays two very distinct emission bands at 470 and 495 nm together with a faint one at 545 nm. It should be noted that in the rigid matrix at 77 K, methanol coordination to the copper(II) center in the excited state is not operative.

#### **4.4 Copper(I) grid complexes**

182 Current Trends in X-Ray Crystallography

diffusion of Et2O into the concentrated solution at 273 K for several days [39]. These complexes are centrosymmetric dimers with pairs of Cu(PPh3)2 units bridged (Mepk)2en. The solid-state structure of complex 29 reveals copper(I) ion coordinated to two N atoms of one Schiff base ligand and two P from two PPh3 (Scheme 32). The central Cu(I) ion has the common irregular pseudo-tetrahedral geometry arising from the low intraligands N-Cu-N chelate angles 79.4(2)° and the P-Cu-P angle is 118.24(7)°. The N-Cu-P bond angles range from 111 to 120°, i.e. slightly more than in a regular tetrahedron (109.5°). The P-Cu-P angle has opened up due to the steric effect from the bulky PPh3 ligands. The CuCu' separation distance 7.06(1) Å in 29 is longer than that observed in 27 (6.2577(6) Å) which is also caused

**N**

**H3C**

**Ph3P**

**Cu**

**N**

**PPh3**

**ClO4**

**(ClO4)2**

by steric effect of PPh3 ligand and also ClO4 anions.

**Ph3P**

Scheme 32.

Scheme 33.

**N**

**CH3**

**N N**

**H H**

**N N Cu**

The ligand L38 is a 2:1 condensate of benzaldehyde and triethylenetetramine (trien). The reaction of ba2trien in the presences of [Cu(CH3CN)4]ClO4 (1:1 molar ratio) in degassed methanol under N2 atmosphere yielded reddish yellow precipitates of mononuclear copper(I) complexe [Cu(ba2trien)]ClO4 (30) [37] (Scheme 33). Single crystals of 30, were grown by slow evaporation of dichloromethane-hexane mixture. The N4 coordination sphere of the copper(I) ion is significantly distorted from tetrahedral due to the steric constraints of the ligand with the Cu-Nimino bond lengths shorter than the Cu-Namino ones.

**PPh3**

**Cu**

**N**

In recent years, grid complexes have been targeted by many researchers as a template to arrange two bidentate ligand binding pockets orthogonal to each other. Brooker *et al*. systematically studied on grid complexes of first transition metal ions that exhibit interesting structural, electrochemical and magnetic properties [31,32, 87-90]. The flat bisbidentate ligand dppn [3,6-bis(2-pyridiyl)pyridazine] has been used for preparation of copper(I) gridlike complexes in 1992 (Scheme 34) [91]. In recent years, the incorporation of such grid-forming bis-bidentate Schiff base ligands into dppn has been explored (Scheme 13). They have been prepared from the reaction of 3,6-diformylpyridazine and substituted amino-benzenes. It was suggested that these ligands are preorganised to form a tetranuclear [2 × 2] grid complexes with a tetrahedrally coordinated metal ion such as copper(I) and silver(I) [32].

Scheme 34.

For preparation of grid copper(I) complexes, the bis-bidentate Schiff base ligands (Scheme 25) were suspended in pure dry acetone and degassed with nitrogen for 15 min. An equimolar amount of tetrakis(acetonitrile)copper(I) hexaflurophosphate was added and the reaction mixture refluxed under nitrogen for 2h. The diffusion of Et2O vapour into an acetone solution yielded single crystals of gridelike copper(I) complexes [Cu4(L45)4](PF6)4 (31) and [Cu4(L41)4](PF6)4 (32) (Fig. 5), while the layering of an acetone solution of the complex on benzene gave single crystals of [Cu4(L42)4](PF6)4 (33) (Fig. 5) [32].

While the tetranuclear cations [Cu4(L45)4](PF6)4 and [Cu4(L41)4](PF6)4 has no crystallographic imposed symmetry, the cation [Cu4(L45)4](PF6)4 contains a two-fold rotation axis relating two halves of the grid from the two ligand strands and two copper(I) ions (Fig. 42). In all of the [2 × 2] copper(I) grid complexes, the coordination geometry of the copper(I) centers is a

Structural Diversity on Copper(I) Schiff Base Complexes 185

copper, one Cu-N bond is significantly longer than others. The longer bonds are formed by

**N N**

**Cu**

**N**

**(ClO4)2**

**N**

**N**

Complex 34 does not exhibit any emission in methanol and dichloromethane at ambient temperature, because coordination of the anion ClO4 to the copper(II) center generated in the photoexcited state brings about a special type of quenching [30], while copper(I) complex [Cu2(p2en)2](PF6)2 (35) is as stable as 34 towards aerial oxidation. Upon excitation at 360 or 470 nm, 35 display a single broad emission band with the maxima at 540 nm in

In recent years, Hannon *et al*. have systematically studied on helical metallo-supramolecular arrays with multidentate Schiff bas ligands L47–L50 [27,28,40,71,72]. For this kind of compounds, the ligand must offer sufficient flexibility for multiple strands to wrap around two or more metal centers, and it should also be sufficiently rigid to impose the same stereochemistry as both metals [27,28]. Non-helical isomers arise when the ligand is too flexible to impose the same stereochemistry at both metal centers [27,28]. For example, while the Schiff base ligand L47 is optimal for octahedral metal triple-helix formation [27,28], with tetrahedral metal ions a mixture of double-stranded helices (*rac* isomers) and boxes (*meso* isomers) are formed [27,28] (Scheme 36). These two isomers are in equilibrium in solution and the box is favored enthalpically, while the helix is favored by entropy. Thus at low temperature the box conformation dominates but as the temperature is raised the

Reaction of L47 with monocations, such as copper(I), leads to dinuclear double-stranded complexes with 2:2 stoichiometry [Cu2L472]2+ (36). In the 1H-NMR spectrum of 36, the central

**N**

**Cu**

**N**

**N**

one of the two terminal pyridyl N's.

methanol at room temperature [30].

proportion of helix conformation grows.

Scheme 35.

Scheme 36.

considerably flattened tetrahedron, formed by four nitrogens from the two Schiff base ligands, with significantly different Cu-N bond distances.

Fig. 5. An ORTEP views of 31-33, showing the atomic numbering scheme. H atoms are omitted for clarity.

These complexes show multiple reversible redox couples. As anticipated, the *E*1/2 values are observed to vary depending on the electron donating/withdrawing nature of the substituents. Complex 31, with chloro withdrawing sustituents, exhibits a total of four reversible one-electron reduction processes. It is likely that each of these processes involves reduction of one ligand strand which can also be taken as a supporting evidence for the existence of the tetranuclear grid structure. For the two complexes 32 and 33 all of the processes are shifted anodically, and hence the initial portion of the reversible couple is swamped by a strong stripping peak, preventing this fourth process from being resolved [32].

#### **4.5 Double-stranded dinuclear copper(I) helicate complexes**

Helicity continues to receive considerable attention as it allows for better understanding of the self-assembly processes involved in supramolecular chemistry [92]. Until now, many examples of both single and double-stranded architectures have now been reported [92]. Studies on inorganic helical complexes containing transition metal ions have attracted much attention recently [27-29,40,67-72]. In these supramolecular self-assembleies, the formation of the helicates can be described as the result of reading molecular information stored in the ligands by metal ions following the coordination algorithm such as tetrahedral. It seems that the self-assembly process of supramolecular helicates is not only controlled by the coordination geometry of metal ions and flexibility of the spacer groups in the ligand, but also influenced by the linkage mode of the spacer group [27-29,40,67-72].

Recently Pal *et al*. have reported a double-stranded, dinuclear, homotopic and neutral copper(I) helicate [Cu2(p2en)2](ClO4)2 (34) with L4 [30] (Scheme 35). Copper(I) complex 34 has been obtained by reaction of p2en with [Cu(CH3CN)4]ClO4 in equimolar proportion in anhydrous methanol under N2 atmosphere. This complex is quite stable in solid state as well as in methanol or dichloromethane solution towards aerial oxidation. It is found to be a double-stranded helicate. The N4 coordination sphere around each copper center is distorted tetrahedral, with angles in the range 80.2 – 81.3° (chelate angles) and 116.2 – 136.6° (interligand ones). The Cu-N bond distances are in the range 2.007 – 2.110 Å. For each copper, one Cu-N bond is significantly longer than others. The longer bonds are formed by one of the two terminal pyridyl N's.

Scheme 35.

184 Current Trends in X-Ray Crystallography

considerably flattened tetrahedron, formed by four nitrogens from the two Schiff base

31 32 33

**4.5 Double-stranded dinuclear copper(I) helicate complexes** 

also influenced by the linkage mode of the spacer group [27-29,40,67-72].

Fig. 5. An ORTEP views of 31-33, showing the atomic numbering scheme. H atoms are

These complexes show multiple reversible redox couples. As anticipated, the *E*1/2 values are observed to vary depending on the electron donating/withdrawing nature of the substituents. Complex 31, with chloro withdrawing sustituents, exhibits a total of four reversible one-electron reduction processes. It is likely that each of these processes involves reduction of one ligand strand which can also be taken as a supporting evidence for the existence of the tetranuclear grid structure. For the two complexes 32 and 33 all of the processes are shifted anodically, and hence the initial portion of the reversible couple is swamped by a strong stripping peak, preventing this fourth process from being resolved

Helicity continues to receive considerable attention as it allows for better understanding of the self-assembly processes involved in supramolecular chemistry [92]. Until now, many examples of both single and double-stranded architectures have now been reported [92]. Studies on inorganic helical complexes containing transition metal ions have attracted much attention recently [27-29,40,67-72]. In these supramolecular self-assembleies, the formation of the helicates can be described as the result of reading molecular information stored in the ligands by metal ions following the coordination algorithm such as tetrahedral. It seems that the self-assembly process of supramolecular helicates is not only controlled by the coordination geometry of metal ions and flexibility of the spacer groups in the ligand, but

Recently Pal *et al*. have reported a double-stranded, dinuclear, homotopic and neutral copper(I) helicate [Cu2(p2en)2](ClO4)2 (34) with L4 [30] (Scheme 35). Copper(I) complex 34 has been obtained by reaction of p2en with [Cu(CH3CN)4]ClO4 in equimolar proportion in anhydrous methanol under N2 atmosphere. This complex is quite stable in solid state as well as in methanol or dichloromethane solution towards aerial oxidation. It is found to be a double-stranded helicate. The N4 coordination sphere around each copper center is distorted tetrahedral, with angles in the range 80.2 – 81.3° (chelate angles) and 116.2 – 136.6° (interligand ones). The Cu-N bond distances are in the range 2.007 – 2.110 Å. For each

ligands, with significantly different Cu-N bond distances.

omitted for clarity.

[32].

Complex 34 does not exhibit any emission in methanol and dichloromethane at ambient temperature, because coordination of the anion ClO4 to the copper(II) center generated in the photoexcited state brings about a special type of quenching [30], while copper(I) complex [Cu2(p2en)2](PF6)2 (35) is as stable as 34 towards aerial oxidation. Upon excitation at 360 or 470 nm, 35 display a single broad emission band with the maxima at 540 nm in methanol at room temperature [30].

In recent years, Hannon *et al*. have systematically studied on helical metallo-supramolecular arrays with multidentate Schiff bas ligands L47–L50 [27,28,40,71,72]. For this kind of compounds, the ligand must offer sufficient flexibility for multiple strands to wrap around two or more metal centers, and it should also be sufficiently rigid to impose the same stereochemistry as both metals [27,28]. Non-helical isomers arise when the ligand is too flexible to impose the same stereochemistry at both metal centers [27,28]. For example, while the Schiff base ligand L47 is optimal for octahedral metal triple-helix formation [27,28], with tetrahedral metal ions a mixture of double-stranded helices (*rac* isomers) and boxes (*meso* isomers) are formed [27,28] (Scheme 36). These two isomers are in equilibrium in solution and the box is favored enthalpically, while the helix is favored by entropy. Thus at low temperature the box conformation dominates but as the temperature is raised the proportion of helix conformation grows.

Scheme 36.

Reaction of L47 with monocations, such as copper(I), leads to dinuclear double-stranded complexes with 2:2 stoichiometry [Cu2L472]2+ (36). In the 1H-NMR spectrum of 36, the central

Structural Diversity on Copper(I) Schiff Base Complexes 187

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CH2 protons in the helix can be used to identify the two isomers. The CH2 protons in the helix are equivalent and thus appear as a singlet resonance, while in the box they are nonequivalent and thus appear as two doublets [28].

Addition of ethyl groups to the central spacer destabilizes the cyclophane configuration so that only [Cu2L492]2+ (36) helicate isomer is present in solution [70]. This is evident from the 1H-NMR spectrum that reveals single specie at room temperature and low temperature, and the central CH2 resonance as a single confirming the helical conformation [70]. The doublehelicate structure of complex 36 has been further confirmed by crystallography. The double helicate [Cu2L492]2+ cation represents a dicationic cylinder (Scheme 38) where each copper(I) center bound to two pyridylimine units, one from each ligand. Each ligand bridges two copper(I) centers giving rise to the dinuclear-stranded helicate architecture. In [Cu2L502](BF4)2 (37) each ligand bridges two copper(I) centers giving rise to the dinuclearstranded helicate architecture (Scheme 37) [70].

1H-NMR spectra of copper(I) complex 37 have been recorded in CD3NO2 and CD3CN solution. In CD3NO2 solution at room temperature, two sets of resonance signals are observed consistent with the prersence of two solution species, the *meso*- and *rac*-isomers, and while in CD3CN solution at room temperature, a singlet set of resonance signals is observed because the ligands exchange is more rapid in this solvent [40].

Scheme 37.

Scheme 38.

#### **5. References**

186 Current Trends in X-Ray Crystallography

CH2 protons in the helix can be used to identify the two isomers. The CH2 protons in the helix are equivalent and thus appear as a singlet resonance, while in the box they are non-

Addition of ethyl groups to the central spacer destabilizes the cyclophane configuration so that only [Cu2L492]2+ (36) helicate isomer is present in solution [70]. This is evident from the 1H-NMR spectrum that reveals single specie at room temperature and low temperature, and the central CH2 resonance as a single confirming the helical conformation [70]. The doublehelicate structure of complex 36 has been further confirmed by crystallography. The double helicate [Cu2L492]2+ cation represents a dicationic cylinder (Scheme 38) where each copper(I) center bound to two pyridylimine units, one from each ligand. Each ligand bridges two copper(I) centers giving rise to the dinuclear-stranded helicate architecture. In [Cu2L502](BF4)2 (37) each ligand bridges two copper(I) centers giving rise to the dinuclear-

1H-NMR spectra of copper(I) complex 37 have been recorded in CD3NO2 and CD3CN solution. In CD3NO2 solution at room temperature, two sets of resonance signals are observed consistent with the prersence of two solution species, the *meso*- and *rac*-isomers, and while in CD3CN solution at room temperature, a singlet set of resonance signals is

> **N N N N Cu Cu**

**N N N N Cu Cu**

**N N N N**

**N N N N**

**(ClO4)2**

**(ClO4)2**

observed because the ligands exchange is more rapid in this solvent [40].

equivalent and thus appear as two doublets [28].

stranded helicate architecture (Scheme 37) [70].

Scheme 37.

Scheme 38.


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**8** 

Olga V. Kovalchukova

*Russian Federation* 

*Peoples' Friendship University of Russia* 

**Features of Structure, Geometrical, and Spectral** 

Coordinate compounds of copper(II) are widely spread both as biological objects (metalloproteins and metallo-enzymes), and in engineering. Among the functions of the copper proteins are: the electron transfer involving the Cu(I)/Cu(II) couple; mono- terminaloxidases*,* which form either water or hydrogen peroxide from dioxygen; oxygenases*,* which incorporate an oxygen atom into a substrate; superoxide degradation to form dioxygen and peroxide; and the oxygen transport*.* From a structural point of view, there are three main types of biologically active copper centres found in the copper proteins (Cowan, 1993). These are "blue" copper centres, where copper atoms are normally coordinated to two nitrogens and two sulphurs, "non-blue" copper centres, where copper atoms are coordinated to two or three nitrogens as well as oxygens, and copper dimers. The nitrogens come from histidine groups, the sulfur from methionine and cysteine, the oxygens from the carboxyllic acid in the protein. So called "non-blue" and dimeric copper-containing proteins are of a a great similarity with complex halo (chloro-, bromo-) cuprates (Abolmaali et al., 1998). Thus, studies of structural and spectral characteristics of anionic complex halides of copper(II) can help to explain electronic structures as well as high reactional abilities and

selectivities of active sites of copper-containing biopolymers in catalytic processes.

halides depend upon structures of their coordination polyhedra (Allen et al., 2009).

structure of complex anions (Rakitin & Kalinnikov, 1994).

It is also evident that anionic halocuprate(II) complexes are catalytically active species responsible for the increased reactivity in a lot of organic reactions (oxidation and polymerization of phenols, reactions of tertiary ammines, dimerization of primary alkyl groups et al.). Various investigations show that catalytic activities of complex copper(II)

And finally, cupric halo-complexes relate to classic magneto-active systems containing 3dmetals, magnetic properties of which significantly depend on features of the spatial

d9-Electronic subshell of Cu(II) is responsible for distortions of symmetry of the coordination polyhedron (Gerloch & Constable, 1994). This deals with the Jahn-Teller effect (as a result of electron-vibrational interactions), and a large spin-orbital interaction constant. These two effects are of comparable values, and this fact complicates the prediction of structures of complexes of such types as well as physico-chemical properties and biological activity of Cu(II) complexes are in many respects determined by features of their structures.

**1. Introduction** 

**Characteristics of the (HL)2[CuX4] and** 

**(HL)2[Cu2X6] (X = Cl, Br) Complexes** 

