**3.5 Structures of compounds containing the Te(-X)4 unit**

122 Current Trends in X-Ray Crystallography

(D) simple chain axial (SC) simple chain equatorial (SC-eq)

chain of dimers (RC-CD) 2d-polymer axial (RC-2d)

Fig. 8. Main supramolecular arrangements of compounds containing the Te(-X)3 unit: dimer (D); simple chain involving only axial halogen atoms (SC) or equatorial halogen atoms (SCeq); 4-membered ring chain: chain of dimers (RC-CD), 2d-polymer involving only axial halogen atoms (RC-2d), and 2d-polymer involving equatorial (RC-2d-eq) halogen atoms

2d-polymer equatorial (RC-2d-eq)

**Dimer** 0 10 4 3 17 **Simple chain** 0 3 1 1 5 **Chain of 4-membered rings** 1 1 2 1 5 **Total** 1 14 7 5 27

a. Dimer. As in Te(-X)1 and Te(-X)2 dimers, two units are linked by two secondary bonds. Axial halogen atoms are involved in them. Dimers are centrosymmetric and the equatorial halogen atom can be in different orientations. In most cases, the angle between the Te-Xeq bond and the normal to planar core is less than 20º but in three cases

b. Simple chain. As in Te(-X)1 and Te(-X)2 simple chains, two units Te(-X)3 are linked by one Te···X secondary bond. The link involves either axial (3 structures) or equatorial halogen (2 structures). As in Te(-X)2 chains, units in Te(-X)3 simple chains are equivalent by screw axes or by glide planes. It is remarkable that in one case, the screw axis is ternary and the chain turns to be helical, vs the zigzag disposition of the chains where

c. In chains of 4-membered rings two cases have been found. In one of them, rings are defined by one axial halogen and the equatorial one. Chains are polymers with two Te···X distances (screw binary axis). In the other case, analogous to the Te(-X)2 4 membered ring chains, rings are defined only by axial halogen atoms and two

Table 4. Summary of structures containing the Te(-X)3 unit

this angle is significantly higher, 37-53º.

binary screw axes are present.

dimer

*a*) *b*)

*c*) 4-membered ring chains:

**F Cl Br I Total** 

These compounds are ionic (or zwitterionic) and the coordination around the Te can be described as a tetragonal pyramid with the halogens and the tellurium in the basal plane and the carbon in the apical position of the pyramid. Two supramolecular patterns are relevant: (a) dimers and (b) simple chains (Figure 9, Table 5).

Fig. 9. Main supramolecular arrangements of compounds containing the Te(-X)4 unit


Table 5. Summary of structures containing the Te(-X)4 unit


#### **3.6 Structures of compounds without Te-X units [Te(-X)0]**

This group is very heterogeneous from a chemical point of view, nevertheless some subsets can be established (Figure 10). A first subset (12 structures) was considered where neutral molecules contain one Te and halogen atoms.

This subset can be considered a general case of the compounds studied in the previous sections: now the tellurium atom and the halogens are separated by more than one covalent bond, hereinafter Te(---X)n. Therefore some above described arrangements were also found here: dimer (4 structures), simple chain (2 structures), and chain of dimers (2 structures).

In a second subset of 11 neutral ditellurides, known patterns were also found in more than half the cases, considering them as X---Te-Te---X. Every Te---X unit affords its own arrangement of secondary bonds: dimers (3 structures), and simple chains (3 structures).

Supramolecular Arrangements in Organotellurium Compounds *via* Te**···**Halogen Contacts 125

arrangements were observed for the polymorphic pair while in one case polymorphism is associated to a different packing of the same supramolecular entity (tetramers). Moreover, it

Ca

Fig. 11. Some specific arrangements present in polymorphic structures: Ta tetramer; Ca and

Sb

Cb chains; Sa and Sb sheets

Sa

Ta

is usual to observe a change of dimensionality between polymorphs.

Cb

When Te-Te bridges are considered, arrangements of higher dimensionality can exist. For example, a Te-Te unit can be bridging dimers to afford a chain of dimers.

Analogously, the combination of chains of secondary bonds and Te-Te bridges can give three more complex arrangements: (i) double chains, (ii) sheets composed by parallel chains, and (iii) double sheets linked by perpendicular Te-Te bridges in a grid-like array.

In other neutral molecules having two tellurium atoms separated by other atoms, single chains of secondary bonds linked by the Te---Te core were observed.

The rest of structures (50) are ionic. In 19 of them, tellurium atoms are in the cationic moiety, halogen atoms are in the anion, and one secondary bond links both ions to give an 1:1 adduct. More complex adducts exist when more than two ions or solvent molecules are bonded by Te···X bonds.

Fig. 10. Examples of supramolecular arrangements in the Te(-X)0 group: dimer (D); simple chain (SC); chain of dimers (CD); specific sheet (Se); adduct (A). Superscripts stand for the number of atoms between Te and X atoms

#### **3.7 Additional structural considerations 3.7.1 Polymorphism**

A search for polymorphism was performed in order to study its relation with the arrangement. Eleven organotellurium compounds containing halogen atoms showed two polymorphic structures each one: two in the Te(-X)1 group, seven in the Te(-X)2 group, one in the Te(-X)3 group, and one in the Te(-X)0 group (Figure 11, Table 6). In ten cases, different

When Te-Te bridges are considered, arrangements of higher dimensionality can exist. For

Analogously, the combination of chains of secondary bonds and Te-Te bridges can give three more complex arrangements: (i) double chains, (ii) sheets composed by parallel chains,

In other neutral molecules having two tellurium atoms separated by other atoms, single

The rest of structures (50) are ionic. In 19 of them, tellurium atoms are in the cationic moiety, halogen atoms are in the anion, and one secondary bond links both ions to give an 1:1 adduct. More complex adducts exist when more than two ions or solvent molecules are

YABXEF (D2

)

CLPHTE01 (Se

4 )

Fig. 10. Examples of supramolecular arrangements in the Te(-X)0 group: dimer (D); simple chain (SC); chain of dimers (CD); specific sheet (Se); adduct (A). Superscripts stand for the

A search for polymorphism was performed in order to study its relation with the arrangement. Eleven organotellurium compounds containing halogen atoms showed two polymorphic structures each one: two in the Te(-X)1 group, seven in the Te(-X)2 group, one in the Te(-X)3 group, and one in the Te(-X)0 group (Figure 11, Table 6). In ten cases, different

number of atoms between Te and X atoms

**3.7 Additional structural considerations** 

**3.7.1 Polymorphism** 

JEPBAH (A)

DIHHAE (CD2

)

example, a Te-Te unit can be bridging dimers to afford a chain of dimers.

chains of secondary bonds linked by the Te---Te core were observed.

)

JATWAC (SC<sup>5</sup>

bonded by Te···X bonds.

and (iii) double sheets linked by perpendicular Te-Te bridges in a grid-like array.

arrangements were observed for the polymorphic pair while in one case polymorphism is associated to a different packing of the same supramolecular entity (tetramers). Moreover, it is usual to observe a change of dimensionality between polymorphs.

Fig. 11. Some specific arrangements present in polymorphic structures: Ta tetramer; Ca and Cb chains; Sa and Sb sheets

Supramolecular Arrangements in Organotellurium Compounds *via* Te**···**Halogen Contacts 127

The set of organotellurium structures containing halogen atoms includes three complete series of halo compounds with the same molecular structure but different halogen, X = F, Cl, Br, I (Table 7). In the three series, bromo and iodo members are isostructural. In the second series, the chloro compound is also isostructural. When isostructurality is not present,

**Series F Cl Br I** 

BIBBOE S

BIBCAR N

OPNTED10 SC

Table 7. Supramolecular arrangements in complete halogen series. SC = simple chain; RC = chain of 4-membered rings; S = sheet; N = 3D-network; Cc, Cd, Sc: specific chains and sheet

Partial series of three and two members are also present in the set of compounds studied, and its abundance is significant: 20 and 47 series respectively. In these partial series, isostructurality is also frequent but examples of non-isostructural members with the same

**Series F Cl Br I** 

IDEXIY RC

Table 8. Supramolecular arrangements in partial halogen series. RC = chain of 4-membered

YASVAP RC

IDEXOZ RC

TUWPAC

YASVET RC

RC

TUWPIK RC

BIBCEV Cc

BIBBUK N

DPHTEB01 N

QIXZAY Cc

DIBTEP02 N

> CIFLEI N

QIXZAY03 Cd

DIBTEP10 Sb

CIFLEI01 Cb

KEHBIJ Sc

GETHOC Sc

FPHTEL RC

kind of supramolecular arrangement are present (Table 8).

(Fig. 7); Cb, Sb: specific chain and sheet (Fig. 11)

rings

**3.7.2 Halogen series** 

arrangements are different.


Table 6. Supramolecular arrangements found in polymorphic structures. 0 = no Te···X contacts; D = dimer; SC = simple chain; RC = chain of 4-membered rings; T = tetramer; N = 3D-network; Cc, Cd: specific chains (Fig. 7); Se 4: specific chain (Fig. 10); Ca, Cb, Ta, Sa, Sb: specific chains, tetramer, sheets (Fig. 11); Na specific 3D-network
