Crystallography of solvent mobility, phase transitions and chemical reactions in transition metal complexes of orotate and citrate

Abstract

Transition metal complexes of polyfunctional ligands -- ligands with multiple functional groups -- form molecular solids which change in unpredictable ways when their environments are modified. A cobalt orotate complex has been found to undergo an arrested phase transition that produces a crystalline sample with both triclinic and monoclinic phases present at the same time. The >single-crystal> characterization of this double phase is described, with special attention to the separation of the diffraction patterns of the two phases. Citrate complexes present a rich variety of behaviors in their molecular solids, from chemical reaction to modulation to solvent transport, all non-destructive, which have been studied by single-crystal diffraction. These transformations can be provoked by temperature and dehydration, or other modifications of ambiant conditions. The factors that give rise to this behavior are related to the nature of the structural building blocks of the crystals formed by these complexes.