Synchronic Transformations of Molecular States and Macroscopic Phases in Valence-Tautomeric Complexes

Valence tautomerism (VT) refers to equilibria between two or more different tautomers differing in their charge distributions. This contribution shows how molecular VT occurring in metal-dioxolene complexes (metal = cobalt, manganese) functionalized with long alkyl chains can be coupled with several types of macroscopic phase transformations, such as solid-to-solid and solid-to-liquid transitions and the double-melting phenomenon. Observations of simultaneous transformation of molecular and macroscopic states have led to the concept of synchronic bistability. The central focus in this microreview is on molecular design, thermodynamic basis, and kinetic control of the synchronic bistability. It is demonstrated that a key factor in designing a synchronic transformation is to build up strong interdependent correlations between molecules and their assembled states.