Polymorphism of bis(dineopentoxyphosphorothioyl)diselenide - Correlation of X-ray structure and MAS NMR data

The crystal structures of two polymorphs of the title compound were determi ned by single-crystal X-ray methods and refined both at room temperature an d 250 K. A triclinic and a monoclinic phase were discovered and studied. Bo th modifications are centrosymmetrical layer structures. The numerically cl early significant differences were observed in unit cell volumes as well as in alternating disproportions of distances of atoms being chemically and c rystallographically equivalent as a result of discontinuously distributed c onformational changes along the single bonds. Phase transitions were not ob served by cooling up to 240 K. Lowering temperatures single crystals of bot h phases decompose be-cause of the considerable anisotropy of intermolecula r interaction. The small differences of molecular structure produce slightl y splitted P-31 CP MAS NMR signals. A comparison of the chemical shifts fro m C-13 CP MAS NMR spectra and from quantum-chemical calculations leads to t he conclusion that the inner rotation around CH2-C-q bonds is not frozen in the solid state.