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)2(N)P(=Y) (Y is O and S) skeleton

Abstract

The crystal structures of N,N′-(cyclohexane-1,4-diyl)bis(O,O′-diphenylphosphoramide), C30H32N2O6P2 or (C6H5O)2P(O)(1-NH)(C6H10)(4-NH)P(O)(OC6H5)2, (I), and N,N′-(1,4-phenylene)bis(O,O′-dimethylthiophosphoramide), C10H18N2O4P2S2 or (CH3O)2P(S)(1-NH)(C6H4)(4-NH)P(S)(OCH3)2, (II), have been investigated. In the structure of (I), with an (O)2(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)2(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.