Solid-state reactions, dynamics in molecular crystals

Abstract

The mechanism of solid-state reactions has found much interest over the years. The hypothesis of minimal atomic and molecular movements did not withstand experimental scrutiny by supermicroscopy. Rather the occurrence of far-reaching and strictly lattice-controlled molecular migrations has been proven for reactions with change of the molecular shape. The crystal packing gives now much more profound information than the mere listing of distances of reaction centers. Topotactic single crystal to single crystal reactions may occur if the molecular shape does not change. Local atomic force microscopy should secure such behaviour, as several claims of topotaxy could not be supported by local experimental techniques. The dynamics in reacting crystals (migrating molecules use ‘easy ways’) can also be triggered by mechanical stress. Most importantly, the new theory encourages the development of unforeseen benign gas–solid and solid–solid reactions which use the same solid-state mechanism as thermal and photochemical conversions. None of the stoichiometric 100% yield reactions would be possible without the long-range molecular movements in the reacting crystals.