**4. General features of phosphoramidate compounds**

## *Compounds with formula RC(O)NHP(O)[NR1R2]2 and RC(O)NHP(O)[NHR1]2*

The four different groups linked to the P atom result in a distorted tetrahedral configuration; as one instance, the bond angles around the P atom of P(O)[NHC(O)CF3][NHCH2C6H4(2-Cl)]2 range from 102.67(12)° to 117.60(12)° [87]. In the

Phosphoramidates: Molecular Packing and Hydrogen

Bond Strength in Compounds Having a P(O)(N)n(O)3-n (n = 1, 2, 3) Skeleton 573

Fig. 2. A view of the PCC mean plane which is crossed from the phosphorus and carbon

Fig. 3. A general view of a 1,3-diazaphosphorinane, a six-membered ring heterocyclic phosphorus compound (the carbon-bonded H atoms were omitted for clarity). The grey big

The hydrogen bond pattern of compounds having the C(O)NHP(O)(N)2 and C(O)NHP(O)(NH)2 skeletons may be predictable with considering the following "empirical

ball in the figure may be RC(O)NH, RNH or the other moieties.

[C6H5O]2P(O)[NC4H8N]P(O)[OC6H5]2 (the molecule is organized around an inversion center located at the centre of the piperazine ring), the N atom environment shows some deviation from planarity. The balls representation denote to the P (orange), N (blue) and C (grey)

atoms shown as balls in the right-side [C6H5O]2P(O)(NC2H4) moiety of

atoms.

rules":

C(O)NHP(O) moiety, however, the carbonyl and phosphoryl groups are separated from each other with one N-H unit, but the terms *syn*, *gauche* and *anti* were used for the description of the C(O) orientation versus P(O) in the literatures [10,26]. Up to now, both *gauche* and *anti* orientations were found for phosphoric triamide compounds having a C(O)NHP(O) skeleton, respectively in 14 and 98 structures (from the 119 structurally reported compounds, 7 cifs are not available). Among them, for the acyclic compounds of the type RC(O)NHP(O)[NHR1]2, merely, the *anti* orientation was reported, so far.

Fig. 1. indicates a general view of compounds with formula CF3C(O)NHP(O)[NHR]2.

In the C(O)NHP(O) moiety, the P—N bond is longer and the O—P—N angle is contracted compared with the respective values in the [P(O)NHR]2 section. For the phosphoramidate compounds, each N atom bonded to phosphorus has a sp2 character which is reflected in the C—N—P angles of the C(O)NHP(O) or C—NH—P moiety or sum of the surrounding angles around the tertiary nitrogen atom (C—N—C + C—N—P + P—N—C). The deviation of this summation from 360º (to a lower value) has been used to show the deviation of nitrogen atom environment from planarity. This may be also illustrated with the distance between the position of N atom from the plane crossing from the directly attached atoms to nitrogen, i.e. C, C and P. In [C6H5O]2P(O)[NC4H8N]P(O)[OC6H5]2 (Fig. 2) which belongs to the amidophosphoric acid ester family, the N atom shows some deviation from planarity and it is 0.25(1) Å above (or below) the CCP plane [61]. For the phosphoramidate compounds, the P-N bonds are shorter than the P-N single bond and the P=O bond are longer than the normal P=O bond [88].

Fig. 1. A typical view for a compound with formula CF3C(O)NHP(O)[NHR]2 [Color key: O atoms are red, the N atom of C(O)NHP(O) is light blue, the other amido N atoms are dark blue, F atoms are yellowish green., C and H atoms are light grey and P atom is orange]; the R substituents are shown as big balls.

In 1,3-diazaphosphorinane compounds, the P=O bond is placed in an equatorial position and the aliphatic six-membered rings adopt conformation between chair and envelope (Fig. 3).

C(O)NHP(O) moiety, however, the carbonyl and phosphoryl groups are separated from each other with one N-H unit, but the terms *syn*, *gauche* and *anti* were used for the description of the C(O) orientation versus P(O) in the literatures [10,26]. Up to now, both *gauche* and *anti* orientations were found for phosphoric triamide compounds having a C(O)NHP(O) skeleton, respectively in 14 and 98 structures (from the 119 structurally reported compounds, 7 cifs are not available). Among them, for the acyclic compounds of

the type RC(O)NHP(O)[NHR1]2, merely, the *anti* orientation was reported, so far.

normal P=O bond [88].

R substituents are shown as big balls.

(Fig. 3).

Fig. 1. indicates a general view of compounds with formula CF3C(O)NHP(O)[NHR]2.

In the C(O)NHP(O) moiety, the P—N bond is longer and the O—P—N angle is contracted compared with the respective values in the [P(O)NHR]2 section. For the phosphoramidate compounds, each N atom bonded to phosphorus has a sp2 character which is reflected in the C—N—P angles of the C(O)NHP(O) or C—NH—P moiety or sum of the surrounding angles around the tertiary nitrogen atom (C—N—C + C—N—P + P—N—C). The deviation of this summation from 360º (to a lower value) has been used to show the deviation of nitrogen atom environment from planarity. This may be also illustrated with the distance between the position of N atom from the plane crossing from the directly attached atoms to nitrogen, i.e. C, C and P. In [C6H5O]2P(O)[NC4H8N]P(O)[OC6H5]2 (Fig. 2) which belongs to the amidophosphoric acid ester family, the N atom shows some deviation from planarity and it is 0.25(1) Å above (or below) the CCP plane [61]. For the phosphoramidate compounds, the P-N bonds are shorter than the P-N single bond and the P=O bond are longer than the

Fig. 1. A typical view for a compound with formula CF3C(O)NHP(O)[NHR]2 [Color key: O atoms are red, the N atom of C(O)NHP(O) is light blue, the other amido N atoms are dark blue, F atoms are yellowish green., C and H atoms are light grey and P atom is orange]; the

In 1,3-diazaphosphorinane compounds, the P=O bond is placed in an equatorial position and the aliphatic six-membered rings adopt conformation between chair and envelope

Fig. 2. A view of the PCC mean plane which is crossed from the phosphorus and carbon atoms shown as balls in the right-side [C6H5O]2P(O)(NC2H4) moiety of [C6H5O]2P(O)[NC4H8N]P(O)[OC6H5]2 (the molecule is organized around an inversion center located at the centre of the piperazine ring), the N atom environment shows some deviation from planarity. The balls representation denote to the P (orange), N (blue) and C (grey) atoms.

Fig. 3. A general view of a 1,3-diazaphosphorinane, a six-membered ring heterocyclic phosphorus compound (the carbon-bonded H atoms were omitted for clarity). The grey big ball in the figure may be RC(O)NH, RNH or the other moieties.

The hydrogen bond pattern of compounds having the C(O)NHP(O)(N)2 and C(O)NHP(O)(NH)2 skeletons may be predictable with considering the following "empirical rules":

Phosphoramidates: Molecular Packing and Hydrogen

Bond Strength in Compounds Having a P(O)(N)n(O)3-n (n = 1, 2, 3) Skeleton 575

N H O

R3 R2 R2 2 (8)

R2 R<sup>3</sup>

R1 = alkyl, aryl or C(O)R'

P O H

= OR or NR'R'', R3

O

N N

H

R2 2 (12)

Scheme 10. The observed hydrogen bond patterns in compounds having a P(O)NH skeleton

P

C

H N

X

and R3 = OR, NR'R"

H N

P

R1

P

O

= OR, NHR' or NR"R'''

P

N

X

H

O

O C

N H N

R1

N

H H

R3

R2

P

R2

R1

H C(4)

R3

N

R2

= alkyl, aryl or C(O)R, R2

P

C

X

O

H

N

H

N

O

N H O

R2 2 (8)

R1

(such as C(O)NHP(O)[N]2)

R1

O

1. In the reported compounds, the nitrogen atoms bonded to P don't involve in hydrogen bonding interaction as an acceptor (due to their low Lewis base characteristic). Scheme 9 illustrates the possible H-donor sites and H-acceptor centers in the structure of compounds having the C(O)NHP(O)(N)2 and C(O)NHP(O)(NH)2 skeletons.

**donor centers if X or Y = H**

#### **Usually the N atoms don't involve in hydrogen bonding as an acceptor**

Scheme 9. The possible H-donor sites and H-acceptor centers in the C(O)NHP(O)(N)2 and C(O)NHP(O)(NH)2 skeletons (the R, X or Y groups may also be contained the additional Hdonor or H-acceptor sites in their structures which may be involved in the H-bond pattern, the curved arrow shows that the orientation of C=O versus P=O may change)


1. In the reported compounds, the nitrogen atoms bonded to P don't involve in hydrogen bonding interaction as an acceptor (due to their low Lewis base characteristic). Scheme 9 illustrates the possible H-donor sites and H-acceptor centers in the structure of

**N**

**X**

**donor centers if X or Y = H**

**X Y**

compounds having the C(O)NHP(O)(N)2 and C(O)NHP(O)(NH)2 skeletons.

**O**

**C**

**H-donor**

**R**

be noted, later.

R2

conformations were found.

double-H bond acceptor, see: ref. [89]).

**N H**

**H-acceptors**

**Y**

**P**

**N**

**Usually the N atoms don't involve in hydrogen bonding as an acceptor**

the curved arrow shows that the orientation of C=O versus P=O may change)

2. The P=O is a better H-acceptor than the C=O counterpart.

Scheme 9. The possible H-donor sites and H-acceptor centers in the C(O)NHP(O)(N)2 and C(O)NHP(O)(NH)2 skeletons (the R, X or Y groups may also be contained the additional Hdonor or H-acceptor sites in their structures which may be involved in the H-bond pattern,

3. In compounds having a C(O)NHP(O)(N)2 skeleton, i.e. with formula RC(O)NHP(O)[NR'R"]2, both *gauche* and *anti* orientations of P=O *versus* C=O have been found, so, two kinds of packing are expectable which are seen: a) a 1-D chain for a *gauche* orientation, and b) a dimeric aggregate (as an R22(8) loop; for H-bond motifs of phosphoric triamide, see: ref. [10]) with Ci or C1 symmetry for *anti*. The unique NH proton interacts with the oxygen atom of PO, whereas the CO does not cooperate in HB. Such H-bond patterns may also be expectable for the other phosphoramidate compounds having a P(O)NH group, Scheme 10; however, the other H-bond patterns have also been observed in the other sub-categories with a P(O)NH moiety which will

4. In compounds having a C(O)NHP(O)(NH)2 skeleton, only an *anti* situation has been found in acyclic molecules; however, in diazaphosphorinane molecules both

5. In the crystal packing of acyclic compounds having a C(O)NHP(O)(NH)2 skeleton, adjacent molecules are often linked *via* NC(O)NHP(O)—H…O=P and N—H…O=C (or (N— H)2…O=C) hydrogen bonds, building R22(8) and R22(12) rings (or R22(8) and

2(12)/R21(6)) in a linear arrangement (Scheme 11). However, the existence of a PO…HNR interaction has been observed for a few compounds as tri-centered PO[…HC(O)NHP(O)N][…HNR] and PO[…HNR][…HNR] hydrogen bonding, where the oxygen atom of the phosphoryl group acts as a double H-acceptor (for a definition of a

**O**

R1 = alkyl, aryl or C(O)R, R2 = OR or NR'R'', R3 = OR, NHR' or NR"R'''

Scheme 10. The observed hydrogen bond patterns in compounds having a P(O)NH skeleton (such as C(O)NHP(O)[N]2)

Phosphoramidates: Molecular Packing and Hydrogen

angle is less than 110°

Bond Strength in Compounds Having a P(O)(N)n(O)3-n (n = 1, 2, 3) Skeleton 577

Scheme 12. A sequence of R22(10) (top) and R22(10)/R21(6) rings (bottom) in compounds having a C(O)NHP(O)(NH)2 skeleton; in the existing examples of R22(10)/S6, the N-H…O

N H O

<sup>R</sup> <sup>N</sup>

<sup>O</sup> <sup>O</sup> <sup>O</sup> <sup>O</sup> R2

R2 2 (8) P

C

O

R

R N

H

H

H N

X

P

C

X

O

N

Scheme 13. A four-component cluster in the solvated molecule CCl3C(O)NHP(O)[NHC6H11]2.C4H8O2(X = CCl3, R = C6H11)

R N

H

1 (6)

H

O

Scheme 11. A sequence of R22(8) and R22(12) (top), a sequence of R2 2(8) and R22(12)/R21(6) (bottom) rings in compounds having a C(O)NHP(O)(NH)2 skeleton: in these H-bond patterns, the P=O…H-NC(O)NHP(O) and C=O…H-N or C=O…(H-N)2 exist

In most cases of compounds having a C(O)NHP(O)(NH)2 skeleton (containing two Hacceptors–three H-donors), the HBs lead to a 1-D chain. Different 1-D ladder arrangements with tetramer motifs and a linear arrangement with two different kinds of motifs (dimer and tetramer) were also observed. Therefore, two H-donor sites (HNC(O)NHP(O) and one of the HNR) participate with two O atoms in the intermolecular HBs, the other HNR may act as the three following manners: (a) in an intramolecular HB with C(O), (b) in a weaker HB with P(O) as the above mentioned tri-centered HB and (c) without cooperation in any HB.


O

N

N

R2 2 (12)

H

H

2(10) (or R22(10)/R21(6) or R22(10)/S6) may be expected when the C=O is

O C

N

H N

H

R2 1 (6)

P

N

X

H

1(6)

1(6) is formed

O

P

Scheme 11. A sequence of R22(8) and R22(12) (top), a sequence of R22(8) and R22(12)/R2

(bottom) rings in compounds having a C(O)NHP(O)(NH)2 skeleton: in these H-bond

In most cases of compounds having a C(O)NHP(O)(NH)2 skeleton (containing two Hacceptors–three H-donors), the HBs lead to a 1-D chain. Different 1-D ladder arrangements with tetramer motifs and a linear arrangement with two different kinds of motifs (dimer and tetramer) were also observed. Therefore, two H-donor sites (HNC(O)NHP(O) and one of the HNR) participate with two O atoms in the intermolecular HBs, the other HNR may act as the three following manners: (a) in an intramolecular HB with C(O), (b) in a weaker HB with P(O) as the above mentioned tri-centered HB and (c)

hydrogen-bonded to the NC(O)NHP(O)-H unit and the P=O interacts with the Namide-H unit. If the remaining Namide-H unit is involved in an intramolecular hydrogen bond with the oxygen of carbonyl, the R22(10)/S6- graph-set is formed, in this case the oxygen atom of carbonyl acts as a double-H acceptor. In the case of involving this N-H unit in

7. In a solvated molecule [90], the hydrogen-bond pattern may not be predictable, but

8. The investigation for the phosphoric triamide containing a C(O)NHP(O)(NH)2 skeleton shows that in eleven structures the carbonyl oxygen atom acts as a double-H acceptor *via* C(O)...(H—N)(H—N) grouping (in the R22(12)/R21(6) motifs) and in ten structures the phosphoryl oxygen atom acts as a double-H acceptor *via* P(O)…(H— N)(H—N) or P(O)…(H—N)(H—NC(O)NHP(O)) groups in the R22(12)/R21(6) rings or R22(10)/R21(6) ring or in the 1-D ladder arrangement). In the other such phosphoramidate compounds the remaining N—H unit doesn't cooperate in Hbonding interaction. The unique found structure of phosphoramidate with a

the H-bonding interaction with the oxygen of phosphoryl, the R22(10)/R2

some previously mentioned rules may be beneficial, Scheme 13.

C(O)NHP(O)Cl2 skeleton is CF3C(O)NHP(O)Cl2 [91].

patterns, the P=O…H-NC(O)NHP(O) and C=O…H-N or C=O…(H-N)2 exist

C

H N

X

P

C

X

O

without cooperation in any HB.

6. A sequence of R2

(Scheme 12).

H N

N

H

O

N H O

R2 2 (8)

Scheme 12. A sequence of R22(10) (top) and R22(10)/R21(6) rings (bottom) in compounds having a C(O)NHP(O)(NH)2 skeleton; in the existing examples of R2 2(10)/S6, the N-H…O angle is less than 110°

Scheme 13. A four-component cluster in the solvated molecule CCl3C(O)NHP(O)[NHC6H11]2.C4H8O2(X = CCl3, R = C6H11)

Phosphoramidates: Molecular Packing and Hydrogen

Schemes 20 and 21) were reported.

*compounds* 

Bond Strength in Compounds Having a P(O)(N)n(O)3-n (n = 1, 2, 3) Skeleton 579

*Compounds with formula [R1R2N][R3R4N][R5R6N]P(O), [RNH][R1R2N][R3R4N]P(O), [R1NH][R2NH][R3R4N]P(O), [R1NH][R2NH][R3NH]P(O) or more complicated phosphoric triamide* 

Tris-alkyl (aryl) amido phosphates of the formula [R1R2N]3P(O), with three equal amido substituents linked to the P atom, are easily prepared from a one-pot reaction between phosphoryl chloride and corresponding amine. The single crystal X-ray determinations were performed for [R1R2N] = NHCH3 (KABVAL) [93], N(CH3)2 (POTJAJ) [94], NHC(CH3)3 (KABVEP) [93], NHC6H5 (KEQLUO) [95], NHCH2C6H5 (TOKXIB) [96] and NHC6H4(4- OCH3) (WAWNIS) [97] and also for the substituents shown in Scheme 17 [98-105]. Moreover, a few other phosphoramide compounds which each contains a triamido moiety (like for example compounds with refcodes EDEVAK [106] and NUVSEC [107] (Schemes 18 and 19) and some co-crystal compounds (for example BARHMP [108] and VAFRIE [109], see

Fig. 4. A view of the H-bonded centrosymmetric four-component cluster in the crystal packing of {C6H11NH2CH3}+{CF3C(O)NP(O)[N(CH3)(C6H11)]2}- (top) and {C6H11NH2CH3}+{4- CH3C6H4S(O)2NP(O)[N(CH3)(C6H11)]2}- (bottom); the N—H···O hydrogen bonds are shown

#### *Proton transfer compounds*

In the proton transfer compounds containing a {[C(O)NP(O)][N]2} skeleton (Scheme 14), the P-N bond in the [C(O)NP(O)] fragment is shorter than the two other P-N bonds, one example for such compounds is [C6H11NH2CH3][CF3C(O)NP(O)[N(CH3)(C6H11)]2] in which the phosphoryl and carbonyl groups are staggered [O-P-N-C = 64.8(3)º] [80].

Scheme 14. The {[C(O)NP(O)][N]2}- skeleton

The hydrogen bonds (Scheme 15) in such compounds, of the type charge-assisted and also polarization-assisted HBs [92], are strong, reflecting in the distances between the donor and acceptor atoms. Scheme 16 shows a polarization-assisted hydrogen bond in a neutral phosphoramidate, for comparison.

Scheme 15. Contribution of two factors in strengthening of hydrogen bonds (charge and polarization) in the proton-transfer compounds: charge and polarization-assisted hydrogen bonds

Two reported crystal structures of this category, [C6H11NH2CH3][CF3C(O)NP(O)[N(CH3) (C6H11)]2] [80] and [C6H11NH2CH3][4-CH3-C6H4S(O)2NP(O)[N(CH3)(C6H11)]2] [20], have a similar HB pattern as a centrosymmetric four-component cluster involving two anions and two cations which interact through N—H…O hydrogen bonds (Fig. 4).

Scheme 16. A polarization-assisted hydrogen bond in a neutral phosphorus compound

P-N bond in the [C(O)NP(O)] fragment is shorter than the two other P-N bonds, one example for such compounds is [C6H11NH2CH3][CF3C(O)NP(O)[N(CH3)(C6H11)]2] in which

N

The hydrogen bonds (Scheme 15) in such compounds, of the type charge-assisted and also polarization-assisted HBs [92], are strong, reflecting in the distances between the donor and acceptor atoms. Scheme 16 shows a polarization-assisted hydrogen bond in a neutral

P O H N

Two reported crystal structures of this category, [C6H11NH2CH3][CF3C(O)NP(O)[N(CH3) (C6H11)]2] [80] and [C6H11NH2CH3][4-CH3-C6H4S(O)2NP(O)[N(CH3)(C6H11)]2] [20], have a similar HB pattern as a centrosymmetric four-component cluster involving two anions and

H

O

P

N

Scheme 15. Contribution of two factors in strengthening of hydrogen bonds (charge and polarization) in the proton-transfer compounds: charge and polarization-assisted hydrogen

P

N

N

O

skeleton (Scheme 14), the

In the proton transfer compounds containing a {[C(O)NP(O)][N]2}-

the phosphoryl and carbonyl groups are staggered [O-P-N-C = 64.8(3)º] [80].

O

C

C O

N

two cations which interact through N—H…O hydrogen bonds (Fig. 4).

O

P

O

N

C

Scheme 16. A polarization-assisted hydrogen bond in a neutral phosphorus compound

*Proton transfer compounds* 

Scheme 14. The {[C(O)NP(O)][N]2}- skeleton

phosphoramidate, for comparison.

bonds

*Compounds with formula [R1R2N][R3R4N][R5R6N]P(O), [RNH][R1R2N][R3R4N]P(O), [R1NH][R2NH][R3R4N]P(O), [R1NH][R2NH][R3NH]P(O) or more complicated phosphoric triamide compounds* 

Tris-alkyl (aryl) amido phosphates of the formula [R1R2N]3P(O), with three equal amido substituents linked to the P atom, are easily prepared from a one-pot reaction between phosphoryl chloride and corresponding amine. The single crystal X-ray determinations were performed for [R1R2N] = NHCH3 (KABVAL) [93], N(CH3)2 (POTJAJ) [94], NHC(CH3)3 (KABVEP) [93], NHC6H5 (KEQLUO) [95], NHCH2C6H5 (TOKXIB) [96] and NHC6H4(4- OCH3) (WAWNIS) [97] and also for the substituents shown in Scheme 17 [98-105]. Moreover, a few other phosphoramide compounds which each contains a triamido moiety (like for example compounds with refcodes EDEVAK [106] and NUVSEC [107] (Schemes 18 and 19) and some co-crystal compounds (for example BARHMP [108] and VAFRIE [109], see Schemes 20 and 21) were reported.

Fig. 4. A view of the H-bonded centrosymmetric four-component cluster in the crystal packing of {C6H11NH2CH3}+{CF3C(O)NP(O)[N(CH3)(C6H11)]2}- (top) and {C6H11NH2CH3}+{4- CH3C6H4S(O)2NP(O)[N(CH3)(C6H11)]2}- (bottom); the N—H···O hydrogen bonds are shown

Phosphoramidates: Molecular Packing and Hydrogen

oxide (refcode: EDEVAK [106])

(NUVSEC [107])

Bond Strength in Compounds Having a P(O)(N)n(O)3-n (n = 1, 2, 3) Skeleton 581

P

N N

H3C CH3

N

N

HN NH

O O

Et Et

2

O

CH3

Ph

O

Scheme 18. 4,6,9-Tris(1-phenylethyl)-1,4,6,9-tetraaza-5-phosphabicyclo(3.3.3) undecane P-

Scheme 19. 10-Oxo-10-phospha-1,4,7-triazatricyclo(5.2.1.04,10)decane monohydrate

N(CH3)2

Scheme 20. Bis(barbital)-hexamethylphosphoramide complex (BARHMP [108])

O

P

(H3C)2N N(CH3)2

Ph Ph

as dotted lines. The H atoms not involved in hydrogen bonding have been omitted for the sake of clarity and the 4-CH3-C6H4 (bottom) and C6H11 and CH3 substituents are shown as balls (the N…O distances are 2.771(3) & 2.804(3) Å and 2.648(4) & 2.864(4) Å, respectively).

1There is the hydrogen-bonded amide molecule in the structure, i.e. the formula is C24H36N3O7P1,C8H13N1O2. 2There is the solvent C2H5OH molecule in the structure, i.e. the formula is C21H24N3O1P1,C2H6O1. 3The formula is C21H24N3O1P1,2(C7H10N11+),2(Cl11-). 4The formula is C15H15N6O1P1,H2O1.

Scheme 17. The structurally investigated compounds of the formula [R1R2N]3P(O) or [R1R2N]3P(O).B, where B is a hydrogen-bonded species to phosphoric triamide (the related amido moieties and the CSD refcode are presented)

In the crystal packing of molecules having a P(O)(NH)3 skeleton, hydrogen bonded 1-D chain, 1-D ladder, 2-D layer and 3-D arrangements were found. Three different types of 1-D arrangement are formed respectively through a P=O…(H-N)3 or P=O…(H-N)2 groups or *via* the P=O…H-N hydrogen bond. In the two latter cases, respectively one and two N-H units don't cooperate in the hydrogen bond interaction. One example of a linear arrangement, involving the N—H···O and N—H···N HBs, is also found in the structure of P(O)(NH— C5H4N)3 (LAFNAI) [100] in which the pyridine nitrogen atom is involving in the HB pattern as an acceptor, too. As, the phosphoryl oxygen atom may cooperate in H-bonding interaction as a double- or a triple- acceptor, some examples of 2-D and 3-D arrangements have also been found in this class of compounds.

Some phosphoric triamides [R1R2N][R3R4N][R5R6N]P(O) (where merely tertiary nitrogen atoms exist in the structure of molecule) have been reported (for example see: Scheme 22 [110]). Structures with a P(O)(N)3 skeleton, where "N" is a tertiary nitrogen atom, do not show any classical (normal) hydrogen bonding in their crystal packing if the substituent involving the N atom doesn't contain the hydrogen linked to an electronegative atom.

as dotted lines. The H atoms not involved in hydrogen bonding have been omitted for the sake of clarity and the 4-CH3-C6H4 (bottom) and C6H11 and CH3 substituents are shown

as balls (the N…O distances are 2.771(3) & 2.804(3) Å and 2.648(4) & 2.864(4) Å,

OH

BIVYAG [98] JEKLER [99] LAFNAI [100] QONBEB [101]

1QUFJIL [102] 2TAZPOX [103] 3TOLZPO [104] 4OLOCEY [105]

Scheme 17. The structurally investigated compounds of the formula [R1R2N]3P(O) or [R1R2N]3P(O).B, where B is a hydrogen-bonded species to phosphoric triamide (the related

C24H36N3O7P1,C8H13N1O2. 2There is the solvent C2H5OH molecule in the structure, i.e. the formula is

In the crystal packing of molecules having a P(O)(NH)3 skeleton, hydrogen bonded 1-D chain, 1-D ladder, 2-D layer and 3-D arrangements were found. Three different types of 1-D arrangement are formed respectively through a P=O…(H-N)3 or P=O…(H-N)2 groups or *via* the P=O…H-N hydrogen bond. In the two latter cases, respectively one and two N-H units don't cooperate in the hydrogen bond interaction. One example of a linear arrangement, involving the N—H···O and N—H···N HBs, is also found in the structure of P(O)(NH— C5H4N)3 (LAFNAI) [100] in which the pyridine nitrogen atom is involving in the HB pattern as an acceptor, too. As, the phosphoryl oxygen atom may cooperate in H-bonding interaction as a double- or a triple- acceptor, some examples of 2-D and 3-D arrangements

Some phosphoric triamides [R1R2N][R3R4N][R5R6N]P(O) (where merely tertiary nitrogen atoms exist in the structure of molecule) have been reported (for example see: Scheme 22 [110]). Structures with a P(O)(N)3 skeleton, where "N" is a tertiary nitrogen atom, do not show any classical (normal) hydrogen bonding in their crystal packing if the substituent involving the N atom doesn't contain the hydrogen linked to an electronegative atom.

1There is the hydrogen-bonded amide molecule in the structure, i.e. the formula is

C21H24N3O1P1,C2H6O1. 3The formula is C21H24N3O1P1,2(C7H10N11+),2(Cl11-). 4The formula is

NHC6H4(4-CH3) NHC6H4(3-CH3)

N

N

NH

N

CH3

N

NH

N

Ph Ph

respectively).

N

O

O

H3C

C15H15N6O1P1,H2O1.

H3C

N

H3C CH3

O

amido moieties and the CSD refcode are presented)

have also been found in this class of compounds.

Scheme 18. 4,6,9-Tris(1-phenylethyl)-1,4,6,9-tetraaza-5-phosphabicyclo(3.3.3) undecane Poxide (refcode: EDEVAK [106])

Scheme 19. 10-Oxo-10-phospha-1,4,7-triazatricyclo(5.2.1.04,10)decane monohydrate (NUVSEC [107])

Scheme 20. Bis(barbital)-hexamethylphosphoramide complex (BARHMP [108])

Phosphoramidates: Molecular Packing and Hydrogen

dimensional H-bonded chain.

interaction as an H-acceptor [111]

Scheme 24. Refcode DIYMED [112]

acceptor.

Bond Strength in Compounds Having a P(O)(N)n(O)3-n (n = 1, 2, 3) Skeleton 583

an H-bonded dimer forms when the P(O) group and the N—H unit have a *syn* orientation with respect to one another. However, in one structure (refcode: DIYMED [112], Scheme 24) with the *syn* orientation of P(O) *versus* N—H, the molecules are aggregated as a one

> N H

> > N

N H

25) and one example as H-bonded tetramer (XAVXEY, Scheme 26) were also found.

H3C

<sup>P</sup> <sup>N</sup> H

HN

O

Scheme 23. One N atom of the diazaphosphorinane ring cooperates in hydrogen bonding

O O

P

If the P(O) adopts an *anti* orientation *versus* NH, an extended 1-D chain arrangement is expectable through the intermolecular PO···HN hydrogen bond which is found for the most of reported compounds. One example without any N—H···O HB (BIFDUP [113], Scheme

In compounds having an (N)P(O)(NH)2 skeleton, three different linear arrangements were observed: a) through P(O)···H—N hydrogen bonds in which one N—H unit doesn't cooperate in H-bonding (NUVROL [107], Scheme 27 and HIVLII [67], Scheme 28), b) through *R*21(6) (in [(CH3)2N]P(O)[NHC6H5]2 [52] and the compound with refcode MIFYIJ [114], Scheme 29 (top)) and c) through *R*22(8) rings ([(CH3)2N]P(O)[NHC5H9]2 [62] and the compound with refcode IKASAP [47], Scheme 29 (bottom)), two latter cases *via* P(O)···(H—N)(H—N) grouping in which the phosphoryl oxygen atom acts as a double-H

In this series, some other H-bond motifs were observed in compounds having an NH2

moiety instead of NHR moiety (BIXFOE [115], GOMDOB [116]), Scheme 30.

H3C CH3

N

O

I

Scheme 21. 5-(Guanidiniocarbonyl)pyrrole-2-carboxylate tris(pyrrolidino)phosphine oxide solvate (VAFRIE [109])

Scheme 22. Refcode BEJNEJ [110]

A search on the CSD shows that the nitrogen atoms bound to phosphorus in phosphoramidate compounds aren't involved in normal H-bonding interaction as an acceptor due to the deviation of each N atom environment from pyramidality after binding to P and decreasing its Lewis base character with respect to the initial amine; so that, merely one example (refcode: HESCEO [111], Scheme 23), belonging to the diazaphosphorinane family, is observed so far with the donor…acceptor (N…N) distance of 3.258(8) Å in which it may be considered as a weak N—H…N—P hydrogen bond.

In compounds having a P(O)(NH)(N)2 skeleton, only the P(O)NH unit cooperates in a HB interaction; so, two expectable HB patterns are the H-bonded dimer (with Ci symmetry; a dimer with C1 symmetry has not reported, so far) and the 1-D chain (Scheme 10). Usually,

HN

NH

OOC

solvate (VAFRIE [109])

Scheme 22. Refcode BEJNEJ [110]

may be considered as a weak N—H…N—P hydrogen bond.

O

N

CH3

O

Scheme 21. 5-(Guanidiniocarbonyl)pyrrole-2-carboxylate tris(pyrrolidino)phosphine oxide

P

N

O

Ph

CH3

Cl

A search on the CSD shows that the nitrogen atoms bound to phosphorus in phosphoramidate compounds aren't involved in normal H-bonding interaction as an acceptor due to the deviation of each N atom environment from pyramidality after binding to P and decreasing its Lewis base character with respect to the initial amine; so that, merely one example (refcode: HESCEO [111], Scheme 23), belonging to the diazaphosphorinane family, is observed so far with the donor…acceptor (N…N) distance of 3.258(8) Å in which it

In compounds having a P(O)(NH)(N)2 skeleton, only the P(O)NH unit cooperates in a HB interaction; so, two expectable HB patterns are the H-bonded dimer (with Ci symmetry; a dimer with C1 symmetry has not reported, so far) and the 1-D chain (Scheme 10). Usually,

N

O

+

NH2

<sup>N</sup> NH2

P

N

Cl

N

an H-bonded dimer forms when the P(O) group and the N—H unit have a *syn* orientation with respect to one another. However, in one structure (refcode: DIYMED [112], Scheme 24) with the *syn* orientation of P(O) *versus* N—H, the molecules are aggregated as a one dimensional H-bonded chain.

Scheme 23. One N atom of the diazaphosphorinane ring cooperates in hydrogen bonding interaction as an H-acceptor [111]

Scheme 24. Refcode DIYMED [112]

If the P(O) adopts an *anti* orientation *versus* NH, an extended 1-D chain arrangement is expectable through the intermolecular PO···HN hydrogen bond which is found for the most of reported compounds. One example without any N—H···O HB (BIFDUP [113], Scheme 25) and one example as H-bonded tetramer (XAVXEY, Scheme 26) were also found.

In compounds having an (N)P(O)(NH)2 skeleton, three different linear arrangements were observed: a) through P(O)···H—N hydrogen bonds in which one N—H unit doesn't cooperate in H-bonding (NUVROL [107], Scheme 27 and HIVLII [67], Scheme 28), b) through *R*21(6) (in [(CH3)2N]P(O)[NHC6H5]2 [52] and the compound with refcode MIFYIJ [114], Scheme 29 (top)) and c) through *R*22(8) rings ([(CH3)2N]P(O)[NHC5H9]2 [62] and the compound with refcode IKASAP [47], Scheme 29 (bottom)), two latter cases *via* P(O)···(H—N)(H—N) grouping in which the phosphoryl oxygen atom acts as a double-H acceptor.

In this series, some other H-bond motifs were observed in compounds having an NH2 moiety instead of NHR moiety (BIXFOE [115], GOMDOB [116]), Scheme 30.

Phosphoramidates: Molecular Packing and Hydrogen

Scheme 28. Refcode HIVLII [67]

Bond Strength in Compounds Having a P(O)(N)n(O)3-n (n = 1, 2, 3) Skeleton 585

CH3

P HN O

N

P

O

H3C CH3

N H

N H

N

H3C CH3

P

O

N

H3C CH3

N H

N H

Scheme 29. Refcodes MIFYIJ (top) [114] and IKASAP (bottom) [47]

N NH

N

Scheme 25. Refcode BIFDUP [113]

Scheme 26. Refcode XAVXEY (any reference to a journal, book and so on was not found for this structure)

Scheme 27. Refcode NUVROL [107]

Scheme 28. Refcode HIVLII [67]

N

CH3

H3C

Scheme 25. Refcode BIFDUP [113]

Scheme 27. Refcode NUVROL [107]

this structure)

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

N

Scheme 26. Refcode XAVXEY (any reference to a journal, book and so on was not found for

P

Ph Ph

O

N H

N

Cl Cl

N H P

Ph Ph

NMe2 O

NH

NH

N P O

N

N

CH3

Scheme 29. Refcodes MIFYIJ (top) [114] and IKASAP (bottom) [47]

Phosphoramidates: Molecular Packing and Hydrogen

in the P(O)NH group.

3.127(3) Å, respectively.

a P(O)(O)(NH)(NH) moiety.

Bond Strength in Compounds Having a P(O)(N)n(O)3-n (n = 1, 2, 3) Skeleton 587

Similar to the other phosphoramidates, each N atom bonded to phosphorus doesn't involve in any HB as an acceptor, showing its low Lewis-base character. In most cases, it has a nearly planar environment [26]. Of course, the nitrogen atom' environment of some substituents, such as aziridinyl, like for example in the compound with refcode GOMDOB [118] (Scheme 30 (bottom)) shows some deviation from planarity, but such N atom doesn't cooperate in hydrogen bonding interaction, too. Moreover, the oxygen atom of the phenoxy or alkoxy groups in the 47 structures with an (O)P(=O)(NH)(N) skeleton (like for example in 4-CH3-C6H4OP(O)[N(CH3)2][NHC(CH3)3], GUDGIW: [119]) doesn't cooperate in the HB interaction, as it can not compete with the phosphoryl oxygen atom for H-accepting from the unique H-donor site in the molecule. Furthermore, among the 106 deposited structures with an (O)(O)P(=O)(NH) skeleton, only the structure of [CH3O]2P(O)[NHCH(CH(CH3) (OC(O)CH3))(C(O)(C(NN)(COOC2H5)))] (IJUMAB: [120]) shows N-H...O(CH3) not N-H...O(P) hydrogen bond (in this consideration, some structures with unavailable cifs were not enumerated). So, such compounds [if the substituents linked to the N or/and O atoms don't contain any H-acceptor or H-donor centers] may be almost always considered as compounds with "one H-acceptor (the oxygen of phosphoryl) and one H-donor sites", both

The oxygen atom of OR moiety in some examples of compounds with a higher H-donor sites, such as compounds containing an (O)P(=O)(NH)(NH) skeleton, however, it has a lower H-acceptability than the phosphoryl oxygen atom, is enforced to involve in the HB interaction ([4-CH3-C6H4O]P(O)[NHC6H4(4-CH3)]2: MUBPIJ, [36]). The better Hacceptability of the phosphoryl O atom than that of the RO moiety, in some cases for example in [C6H5O]P(O)[NHC6H11][NHC6H4(4-CH3)] (ERUFIH: [69]), leads to act it as a double-H acceptor. In the molecular packing of [C6H5O]P(O)[NHC6H11]2.CH3OH (HIVLOO, [67]), a linear arrangement is formed through a P(O)[...H—O][…H—N] grouping, where, the P(O) group acts as a double H-acceptor, the OH unit belongs to the solvent methanol.

In the 2-D H-bonded arrangement for diazaphosphorinane 4-CH3C6H4OP(O)X [X = NHCH2CH2CH2NH (KIVXIX)] and C6H5OP(O)Y [Y = NHCH2C(CH3)2CH2NH (KIVXOD)], the P(O) functions as a double-H acceptor [121]. In the other cases, both O atoms are involved in the HB interactions with two N—H units (or the other H-donor site(s) in the molecule or in the crystal), in which the P(O) forms a stronger HB. Typically, in the crystal packing of [4-CH3-C6H4O]P(O)[NHC6H4(4-CH3)]2 (MUBPIJ, [36]), the N...O(P) = 2.805(2) Å & N...O(C6H4-4-CH3) = 3.068(2) Å and of C6H5OP(O)[NHC6H4(4-CH3)][NHCH2C6H5], in a recently published paper by Pourayoubi *et al.*, 2011 [43], these distances are 2.761(3) Å &

Scheme 31 illustrates the contribution of P(O) as a double-H atom acceptor (top) and cooperation of both oxygen atoms (bottom) in hydrogen bond pattern in compounds having

In the crystal packing of compounds with the general formula (R1O)P(O)[NHR2]2, both linear and 2-D hydrogen-bonded arrangements were observed; for example, C6H5OP(O)[NHC6H11]2.CH3OH (HIVLOO [67]), 4-CH3-C6H4OP(O)[NHC6H4-4-CH3]2 (MUBPIJ [36]), 4-CH3-C6H4OP(O)[NHC6H4-2-CH3]2 (YUPVEL [32]) and 4-CH3-C6H4OP(O)X (X = NHCH2C(CH3)2CH2NH, NIBNOC [83]-a) exist as a linear H-bonded arrangement, whereas a 2-D array is found for instance in each of 4-CH3—C6H4OP(O)X (X =

Scheme 30. Refcodes BIXFOE (top) [115] and GOMDOB (bottom) [116]

*Compounds with formula (R1O)(R2O)(R3R4N)P(O), (R1O)(R2O)(R3NH)P(O), (R1O)(R2R3N) (R4R5N)P(O), (R1O)(R2NH)(R3R4N)P(O) and (R1O)(R2NH)(R3NH)P(O)* 

The tetrahedral configuration of phosphorus atom is significantly distorted as it has been noted for the other phosphoramides and their chalco-derivatives [117]. For example, the bond angles around the P atom of (4-CH3-C6H4O)(C6H11NH)2P(O) [116] vary in the range from 101.48(10)° [for Ophenoxy—P—N1 angle] to 118.58(9)° [for Ophosphoryl—P—N2 angle]. The C—O—P angle is 123.52(15)º. A general view of a compound with formula (4-CH3- C6H4O)(RNH)2P(O) is shown in Fig. 5.

Fig. 5. A general view of a compound with formula (4-CH3-C6H4O)(RNH)2P(O), the R moieties are shown as grey balls.

P

CH3 H3C

N P N

NH2

*Compounds with formula (R1O)(R2O)(R3R4N)P(O), (R1O)(R2O)(R3NH)P(O), (R1O)(R2R3N)* 

The tetrahedral configuration of phosphorus atom is significantly distorted as it has been noted for the other phosphoramides and their chalco-derivatives [117]. For example, the bond angles around the P atom of (4-CH3-C6H4O)(C6H11NH)2P(O) [116] vary in the range from 101.48(10)° [for Ophenoxy—P—N1 angle] to 118.58(9)° [for Ophosphoryl—P—N2 angle]. The C—O—P angle is 123.52(15)º. A general view of a compound with formula (4-CH3-

Fig. 5. A general view of a compound with formula (4-CH3-C6H4O)(RNH)2P(O), the R

PhH2C CH2Ph

H2N O

N

CH3

N

<sup>O</sup> H3C

Scheme 30. Refcodes BIXFOE (top) [115] and GOMDOB (bottom) [116]

*(R4R5N)P(O), (R1O)(R2NH)(R3R4N)P(O) and (R1O)(R2NH)(R3NH)P(O)* 

C6H4O)(RNH)2P(O) is shown in Fig. 5.

moieties are shown as grey balls.

Similar to the other phosphoramidates, each N atom bonded to phosphorus doesn't involve in any HB as an acceptor, showing its low Lewis-base character. In most cases, it has a nearly planar environment [26]. Of course, the nitrogen atom' environment of some substituents, such as aziridinyl, like for example in the compound with refcode GOMDOB [118] (Scheme 30 (bottom)) shows some deviation from planarity, but such N atom doesn't cooperate in hydrogen bonding interaction, too. Moreover, the oxygen atom of the phenoxy or alkoxy groups in the 47 structures with an (O)P(=O)(NH)(N) skeleton (like for example in 4-CH3-C6H4OP(O)[N(CH3)2][NHC(CH3)3], GUDGIW: [119]) doesn't cooperate in the HB interaction, as it can not compete with the phosphoryl oxygen atom for H-accepting from the unique H-donor site in the molecule. Furthermore, among the 106 deposited structures with an (O)(O)P(=O)(NH) skeleton, only the structure of [CH3O]2P(O)[NHCH(CH(CH3) (OC(O)CH3))(C(O)(C(NN)(COOC2H5)))] (IJUMAB: [120]) shows N-H...O(CH3) not N-H...O(P) hydrogen bond (in this consideration, some structures with unavailable cifs were not enumerated). So, such compounds [if the substituents linked to the N or/and O atoms don't contain any H-acceptor or H-donor centers] may be almost always considered as compounds with "one H-acceptor (the oxygen of phosphoryl) and one H-donor sites", both in the P(O)NH group.

The oxygen atom of OR moiety in some examples of compounds with a higher H-donor sites, such as compounds containing an (O)P(=O)(NH)(NH) skeleton, however, it has a lower H-acceptability than the phosphoryl oxygen atom, is enforced to involve in the HB interaction ([4-CH3-C6H4O]P(O)[NHC6H4(4-CH3)]2: MUBPIJ, [36]). The better Hacceptability of the phosphoryl O atom than that of the RO moiety, in some cases for example in [C6H5O]P(O)[NHC6H11][NHC6H4(4-CH3)] (ERUFIH: [69]), leads to act it as a double-H acceptor. In the molecular packing of [C6H5O]P(O)[NHC6H11]2.CH3OH (HIVLOO, [67]), a linear arrangement is formed through a P(O)[...H—O][…H—N] grouping, where, the P(O) group acts as a double H-acceptor, the OH unit belongs to the solvent methanol.

In the 2-D H-bonded arrangement for diazaphosphorinane 4-CH3C6H4OP(O)X [X = NHCH2CH2CH2NH (KIVXIX)] and C6H5OP(O)Y [Y = NHCH2C(CH3)2CH2NH (KIVXOD)], the P(O) functions as a double-H acceptor [121]. In the other cases, both O atoms are involved in the HB interactions with two N—H units (or the other H-donor site(s) in the molecule or in the crystal), in which the P(O) forms a stronger HB. Typically, in the crystal packing of [4-CH3-C6H4O]P(O)[NHC6H4(4-CH3)]2 (MUBPIJ, [36]), the N...O(P) = 2.805(2) Å & N...O(C6H4-4-CH3) = 3.068(2) Å and of C6H5OP(O)[NHC6H4(4-CH3)][NHCH2C6H5], in a recently published paper by Pourayoubi *et al.*, 2011 [43], these distances are 2.761(3) Å & 3.127(3) Å, respectively.

Scheme 31 illustrates the contribution of P(O) as a double-H atom acceptor (top) and cooperation of both oxygen atoms (bottom) in hydrogen bond pattern in compounds having a P(O)(O)(NH)(NH) moiety.

In the crystal packing of compounds with the general formula (R1O)P(O)[NHR2]2, both linear and 2-D hydrogen-bonded arrangements were observed; for example, C6H5OP(O)[NHC6H11]2.CH3OH (HIVLOO [67]), 4-CH3-C6H4OP(O)[NHC6H4-4-CH3]2 (MUBPIJ [36]), 4-CH3-C6H4OP(O)[NHC6H4-2-CH3]2 (YUPVEL [32]) and 4-CH3-C6H4OP(O)X (X = NHCH2C(CH3)2CH2NH, NIBNOC [83]-a) exist as a linear H-bonded arrangement, whereas a 2-D array is found for instance in each of 4-CH3—C6H4OP(O)X (X =

Phosphoramidates: Molecular Packing and Hydrogen

absorbed phosphorus-nitrogen compound in which the Cl-

CH3

Scheme 32. Refcodes PHOXBP (left) [124] and TMPMET (right) [125]

RHN

Scheme 33. Refcode GAHFUS, R = cyclo-hexyl [126]

P

HN

P

O O

4 H2O

N

NHR NHR

NH

NHR

P

N—H units of two-neighboring phosphoramidates.

O

P

HO

H3C

O N

Bond Strength in Compounds Having a P(O)(N)n(O)3-n (n = 1, 2, 3) Skeleton 589

phosphorus-nitrogen compounds' family. The crystal packing of the latter compound

bonds (O…O = 2.43 & 2.50 Å) and relatively strong hetero-conjugated [N—H…O]δ<sup>+</sup> hydrogen bond (N…O = 2.93 Å). In the hydrated zwitterionic compound shown in Scheme 33 (refcode: GAHFUS) [126], the N+ which is lack of the lone electron pair doesn't involve in H-bonding interaction; whereas, the [P(O)(O)]- unit cooperates in some N—H…O and O— H…O hydrogen bonds (Fig. 6). Compounds with refcodes IGASUF (Scheme 34) [127] and WIYFAL (Scheme 35) [128] are respectively a simple phosphate salt and an HCl-water

hydrogen

ion is hydrogen-bonded to the

NH

O

P

<sup>N</sup> <sup>O</sup>

P

HO

O

HN

P

HO O

CH3OH

NH4

H

contains some various HBs such as two very strong homo-conjugated [O—H…O]-

NHCH2CH2CH2NH, KIVXIX [121]), C6H5OP(O)X (X = NHCH2C(CH3)2CH2NH, KIVXOD [83]-a), C6H5OP(O)(NH2)2 (PPOSAM [122]) and C6H5OP(O)X (X = NHNHP(O)(OC6H5) NHNH (FIMVUS [123])).

Scheme 31. A view of contribution of phosphoryl oxygen atom as a double-H acceptor (top) and a view of contribution of both oxygen atoms (bottom) in hydrogen bond pattern of compounds having a P(O)(O)(NH)(NH) skeleton

In summary, the cif files of all published compounds with the (O)P(=O)(NH)2, (O)2P(=O)(NH) and (O)P(=O)(NH)(N) skeletons were investigated and the following "empirical rules" were obtained:


#### *Amidophosphoric acid and amido phosphate compounds*

Compounds with refcodes PHOXBP (Scheme 32, left) [124] and TMPMET (Scheme 32, right) [125] are respectively the examples of an acid and a solvated acidic-salt belonging to the

NHCH2CH2CH2NH, KIVXIX [121]), C6H5OP(O)X (X = NHCH2C(CH3)2CH2NH, KIVXOD [83]-a), C6H5OP(O)(NH2)2 (PPOSAM [122]) and C6H5OP(O)X (X = NHNHP(O)(OC6H5)

Scheme 31. A view of contribution of phosphoryl oxygen atom as a double-H acceptor (top) and a view of contribution of both oxygen atoms (bottom) in hydrogen bond pattern of

In summary, the cif files of all published compounds with the (O)P(=O)(NH)2, (O)2P(=O)(NH) and (O)P(=O)(NH)(N) skeletons were investigated and the following

1. In none of the reported structures, the nitrogen atom doesn't cooperate in HB

2. Almost in all of the compounds having the (O)2P(=O)(NH) and (O)P(=O)(NH)(N) skeletons, the oxygen atom of the phenoxy (or alkoxy) group doesn't cooperate in the HB interaction, as it can't compete with the phosphoryl oxygen atom to H-accepting from the unique H-donor site in the molecule. There is only one example of hydrogen bond of the type N—H...O(R) in this family of compounds in one compound containing

3. The oxygen atom of OR moiety in some examples of compounds with a higher number of H-donor sites relative to the H-acceptor centers, such as compounds containing an (O)P(=O)(NH)2 skeleton, however, it has a lower H-acceptability than the phosphoryl

4. In compounds having an (O)P(=O)(NH)2 skeleton, the better H-acceptability of the phosphoryl O atom than that of the RO moiety, in some cases, leads to act it as a

Compounds with refcodes PHOXBP (Scheme 32, left) [124] and TMPMET (Scheme 32, right) [125] are respectively the examples of an acid and a solvated acidic-salt belonging to the

some H-acceptor centers in addition to one phosphoryl group.

oxygen atom, is enforced to involve in the HB interaction.

*Amidophosphoric acid and amido phosphate compounds*

compounds having a P(O)(O)(NH)(NH) skeleton

"empirical rules" were obtained:

interaction as an acceptor.

double-H acceptor.

NHNH (FIMVUS [123])).

phosphorus-nitrogen compounds' family. The crystal packing of the latter compound contains some various HBs such as two very strong homo-conjugated [O—H…O] hydrogen bonds (O…O = 2.43 & 2.50 Å) and relatively strong hetero-conjugated [N—H…O]δ<sup>+</sup> hydrogen bond (N…O = 2.93 Å). In the hydrated zwitterionic compound shown in Scheme 33 (refcode: GAHFUS) [126], the N+ which is lack of the lone electron pair doesn't involve in H-bonding interaction; whereas, the [P(O)(O)]- unit cooperates in some N—H…O and O— H…O hydrogen bonds (Fig. 6). Compounds with refcodes IGASUF (Scheme 34) [127] and WIYFAL (Scheme 35) [128] are respectively a simple phosphate salt and an HCl-water absorbed phosphorus-nitrogen compound in which the Cl ion is hydrogen-bonded to the N—H units of two-neighboring phosphoramidates.

Scheme 32. Refcodes PHOXBP (left) [124] and TMPMET (right) [125]

Scheme 33. Refcode GAHFUS, R = cyclo-hexyl [126]

Phosphoramidates: Molecular Packing and Hydrogen

O

Scheme 35. Refcode WIYFAL [128]

P

Bond Strength in Compounds Having a P(O)(N)n(O)3-n (n = 1, 2, 3) Skeleton 591

OC2H5

Different orientations resulting from non-rigid units in some molecules and ions and the presence of different H-bonds or the other short contacts may result in two or more conformers (or symmetrically independent molecules (or ions)) in solid state. Compound C6H5C(O)NHP(O)[NH(*tert*-C4H9)]2, exists as two conformers in crystalline lattice (which are detectable in solution, too by NMR experiment) [27]. They are due to different spatial orientations of *tert*-butyl amido groups. One of the two conformers has two NH units (of *tert*-butyl amido moieties) which are *syn*, but not in the other. Another example is the presence of disorder in the cyclic amido moiety. For example, C6H5C(O)NHP(O)[NC4H8]2 appears as two crystallographically independent molecules [55]. This is based on the conformational forms of the pyrrolidinyl groups and the orientation of the phenyl ring. The dimmeric aggregate in this case, between two independent molecules, is not centrosymmetric. The structure of [NH2(C6H11)(*tert*-C4H9)][PO2Cl2] consists of two symmetrically independent dichlorophosphate anions as well as cyclohexyl-*tert*butylammonium cations [75]. In the crystal structure of [*tert*-C4H9NH3][CF3C(O)NHP(O)(O)(*tert*-C4H9NH)].0.333CH3CN.0.333H2O [79], there are three symmetrically independent trifluoroacetyl-N-(*tert*-butylamino) phosphate anions and three independent cations of *tert*-butyl- ammonium; one of the anion indicates disorder in the *tert*-C4H9 moiety. There are some other examples of disordered components for the groups such

Histogram of the N…O distances in the N—H…O hydrogen bonds in compounds having a P(O)(N)n(O)3-n (n = 1, 2, 3) skeleton is given in Fig. 7. In this figure, the distribution of Hbond strength in different families of phosphoramidates are shown with different colored columns: compounds having a P(O)(NH)n(N)m(O)3-(n+m) skeleton (n = 1, 2; n+m < 3) as black

OC2H5

0.5 HCl, 0.25 H2O

P

O

H N

**5. Crystallographically independent molecules and ions** 

as *tert*-C4H9, cyclopentyl and cyclohexyl etc. in the deposited cifs.

**6. Hydrogen bond strengths in phosphoramidates** 

Fig. 6. Fragment of the crystal packing of the hydrated zwitterionic compound with refcode GAHFUS [126] showing the involvement of [P(O)(O)]- units in N—H…O (blue dotted lines) and O—H…O (black dotted lines) hydrogen bonds, two symmetrically independent zwitterionic compounds in the structure are shown as blue and green apart the oxygen atoms of [P(O)(O)] units which are shown as red balls, the water molecules are represented with grey color. The cyclohexyl groups are shown as balls (green and blue).

Scheme 34. Refcode IGASUF [127]

Scheme 35. Refcode WIYFAL [128]

590 Advances in Crystallization Processes

Fig. 6. Fragment of the crystal packing of the hydrated zwitterionic compound with refcode GAHFUS [126] showing the involvement of [P(O)(O)]- units in N—H…O (blue dotted lines) and O—H…O (black dotted lines) hydrogen bonds, two symmetrically independent zwitterionic compounds in the structure are shown as blue and green apart the oxygen

> H N

with grey color. The cyclohexyl groups are shown as balls (green and blue).

P

O-

Et

NH2 +

Et

EtO

Scheme 34. Refcode IGASUF [127]

O

units which are shown as red balls, the water molecules are represented

atoms of [P(O)(O)]-
