Structural and ab initio studies on the polymorphism of iminophosphorane (CH3C6H4)3P=NP[(=O)(OPh)2]

Abstract

Two polymorphic forms of a new iminophosphorane have been investigated by infrared, nuclear magnetic resonance and mass spectroscopy, X-ray crystallography and studied through ab initio quantum chemical calculations. The monoclinic polymorph alpha contains two independent molecules (alpha I and alpha II) in the asymmetric unit, while the orthorhombic polymorph beta has one molecule in the asymmetric unit. The molecules in polymorphs alpha and beta adopt different conformations. Hirshfeld surfaces and fingerprint plots were generated in order to compare the two independent molecules alpha I and alpha II in the asymmetric unit and also for a comparison of beta molecule, in the orthorhombic crystal system, with the previously reported monoclinic polymorph. The results show that the packing motifs in polymorphs alpha and beta differ mainly due to the redistribution of C-H center dot center dot center dot O and C-H center dot center dot center dot pi hydrogen-bond interactions rather than their percentage Hirshfeld surface area contributions. The dipole-dipole interactions significantly influence the intermolecular interactions in polymorphs alpha and beta. The calculated lattice energies indicate that polymorph alpha is slightly more stable than polymorph alpha. (C) 2014 Elsevier B.V. All rights reserved.