In the hydrogen-bond patterns of phenyl bis(2-chlorobenzylamido)phosphinate, C20H19Cl2N2O2P, (I), andN,N′-bis(2-chlorobenzyl)-N′′-(2,2,2-trifluoroacetyl)phosphoric triamide, C16H15Cl2F3N3O2P, (II), the O atoms of the related phosphoryl groups act as double H-atom acceptors, so that the P=O...(H—N)2hydrogen bond in (I) and the P=O...(H—Namide)2and C=O...H—NC(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)2and (NH)2P(=O)OP(=O)(NH)2groups, and (ii) the remarkable H-atom acceptability of this atom relative to the other acceptor centre(s) in molecules containing an OP(=O)(NH)2group, 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)2P(=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) areantiwith 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 linkedviathe above-mentioned hydrogen bonds into a linear arrangement parallel to [100] in both cases, in (I) by formingR22(8) rings and in (II) through a combination ofR22(10) andR21(6) rings.
Doubly ionic hydrogen bond interactions within the choline chloride–urea deep eutectic solvent