Interactions in Polymorphic Crystals of m-Nitrophenol as Studied by Variable-Temperature X-ray Diffraction and Quantum Chemical Calculations

Abstract

Crystal structures of two polymorphic forms of m-nitrophenol have been determined at several temperatures between 95 to 350 K. The thermal expansion tensor and the rigid-body translation and libration tensors have been calculated for both polymorphs at different temperatures. Quantum chemical calculations of interactions for molecular clusters that modeled two polymorphic crystal structures have been performed. The comparison of molecular interaction energies and dynamics in polymorphs has been considered in terms of the large hysteresis of the metastable phase occurrence. Evidence of the reconstructive transition is reported. The molecular mechanism of the transition in one direction is controlled by thermally induced molecular librations coupled with internal torsions of nitro groups. The torsional vibrations of nitro groups are damped in the high-temperature phase making the reverse transformation impossible due to the cooling.