The double H-atom acceptability of the P=O group in new XP(O)(NHCH2C6H4-2-Cl)2 phosphoramidates [X = C6H5O- and CF3C(O)NH-]: a database analysis of compounds having a P(O)(NHR) group.

In the hydrogen-bond patterns of phenyl bis(2-chlorobenzylamido)phosphinate, C(20)H(19)Cl(2)N(2)O(2)P, (I), and N,N'-bis(2-chlorobenzyl)-N''-(2,2,2-trifluoroacetyl)phosphoric triamide, C(16)H(15)Cl(2)F(3)N(3)O(2)P, (II), the O atoms of the related phosphoryl groups act as double H-atom acceptors, so that the P=O···(H-N)(2) hydrogen bond in (I) and the P=O···(H-N(amide))(2) and C=O···H-N(C(O)NHP(O)) hydrogen bonds in (II) are responsible for the aggregation of the molecules in the crystal packing. The presence of a double H-atom acceptor centre is a result of the involvement of a greater number of H-atom donor sites with a smaller number of H-atom acceptor sites in the hydrogen-bonding interactions. This article also reviews structures having a P(O)NH group, with the aim of finding similar three-centre hydrogen bonds in the packing of phosphoramidate compounds. This analysis shows that the factors affecting the preference of the above-mentioned O atom to act as a double H-atom acceptor are: (i) a higher number of H-atom donor sites relative to H-atom acceptor centres in molecules with P(=O)(NH)(3), (N)P(=O)(NH)(2), C(=O)NHP(=O)(NH)(2) and (NH)(2)P(=O)OP(=O)(NH)(2) groups, and (ii) the remarkable H-atom acceptability of this atom relative to the other acceptor centre(s) in molecules containing an OP(=O)(NH)(2) group, with the explanation that the N atom bound to the P atom in almost all of the structures found does not take part in hydrogen bonding as an acceptor. Moreover, the differences in the H-atom acceptability of the phosphoryl O atom relative to the O atom of the alkoxy or phenoxy groups in amidophosphoric acid esters may be illustrated by considering the molecular packing of compounds having (O)(2)P(=O)(NH) and (O)P(=O)(NH)(N)groups, in which the unique N-H unit in the above-mentioned molecules almost always selects the phosphoryl O atom as a partner in forming hydrogen-bond interactions. The P atoms in (I) and (II) are in tetrahedral coordination environments, and the phosphoryl and carbonyl groups in (II) are anti with respect to each other (the P and C groups are separated by one N atom). In the crystal structures of (I) and (II), adjacent molecules are linked via the above-mentioned hydrogen bonds into a linear arrangement parallel to [100] in both cases, in (I) by forming R(2)(2)(8) rings and in (II) through a combination of R(2)(2)(10) and R(2)(1)(6) rings.