Polymorphism, weak interactions and phase transitions in chalcogen-phosphorus heterocycles

Abstract

A series of novel P-E containing heterocycles with aromatic backbones were synthesised and characterized by single crystal and powder X-ray diffraction, microanalysis and mass spectrometry. 31P and 77Se solution- and solid-state NMR spectroscopy revealed significant differences between the NMR parameters in solution and in the solid state, related to conformational changes in the molecules. Many compounds were shown to exhibit a number of different polymorphic structures (identified by single-crystal XRD), although the bulk material studied by solid-state NMR often contained just one major polymorph. For the unoxidised heterocycles, the presence of weak intermolecular J couplings were also investigated using DFT calcaulations.