A combined X-ray crystallography and theoretical study of N-H...OX (X is =P and -C) hydrogen bonds in two new structures with a (C-O)(N)P(=Y) (Y is O and S) skeleton.

The crystal structures of N,N'-(cyclohexane-1,4-diyl)bis(O,O'-diphenylphosphoramide), CHNOP or (CHO)P(O)(1-NH)(CH)(4-NH)P(O)(OCH), (I), and N,N'-(1,4-phenylene)bis(O,O'-dimethylthiophosphoramide), CHNOPS or (CHO)P(S)(1-NH)(CH)(4-NH)P(S)(OCH), (II), have been investigated. In the structure of (I), with an (O)(N)P(O) skeleton, two symmetry-independent phosphoramide molecules are linked through N-H...O=P hydrogen bonds. In the structure of (II), with an (O)(N)P(S) skeleton, the ester O atoms take part in N-H...O-C hydrogen bonds as acceptors; the P=S groups do not participate in hydrogen-bonding interactions. The strengths of these hydrogen bonds were evaluated, using quantum chemical calculations with the GAUSSIAN09 software package at the B3LYP/6-311G(d,p) level of theory. For this, LP(O) to σ*(NH) charge transfers were studied, according to the second-order perturbation theory in natural bond orbital (NBO) methodology, for a three-component cluster of hydrogen-bonded molecules for both structures, including all of the independent N-H...O hydrogen bonds observed in the crystal packing. The details of the intermolecular interactions were studied by Hirshfeld surface maps and two-dimensional fingerprint plots.