Short-range order, thermal vibration and expansion, and other properties of pseudosymmetric and mixed crystals of small organic molecules - Calculation of dimensions of ordered regions in triclinic and monoclinic pseudosymmetic crystals from the intensity of diffuse scattering

Abstract

Mathematical relations are obtained giving the X-ray scattering for a crystal the unit cell of which contains one or two asymmetric molecules, each of which can adopt either of two centrosymmetrically-related orientations, giving pseudocentrosymmetry. It is shown that measurements of the integral breadth of maxima of the diffuse ‘disorder’ scattering can give the dimensions of the short-range order regions. The temperature variation of intensity of such diffuse scattering is different from that of thermal diffuse scattering.