Disorder and Motion in Crystal Structures: Nuisance and Opportunities

Abstract

Conventional structure analysis averages the structure of an entire crystal into a single unit cell. If there is disorder and thermal motion, this averaging obscures information on local structure, intermolecular interactions and molecular dynamics. Nonetheless structural detail at the molecular and supramolecular level can be retrieved even for heavily disordered molecular materials by analyzing their diffuse scattering. Molecular dynamics can be elucidated and distinguished from disorder on the basis of atomic displacement parameters (ADPs) determined over a range of temperatures from conventional structure analyses. Such studies are now becoming feasible for molecular crystals through improved experimental techniques, faster computers and new algorithms.