Reversible Solid-to-Liquid Phase Transition of Coordination Polymer Crystals

The solid-to-liquid
phase transition, a fundamental process commonly
observed for various types of substances with significant potential
for application, has been given little attention in the field of coordination
polymers (CPs) despite the rich functionality of these compounds.
In this article, we report the reversible solid-to-liquid phase transition
of crystalline CPs. These CPs are composed of zinc ions, phosphate,
and azoles, and a well-balanced composition, ionicity, and bond strength
afford “melting” CPs. We examined the structure of one
such melting framework in the liquid and glass states and found that
the coordination bonds are not fully preserved in the liquid state
but are re-formed in the glass state. As a demonstration, we fabricated,
via phase transition, a thin film with an aligned crystal orientation
and a monolith crystal of the CP.