Indium Imidazolate Frameworks with Differently Distorted ReO3-Type Structures: Syntheses, Structures, Phase Transitions, and Crystallization Studies

Abstract

Three indium imidazolates have been prepared by employing solvothermal, ionothermal, and solventless syntheses. The crystal structures have been determined using laboratory powder XRD methods in combination with DFT calculations. In phases I–III, octahedrally coordinated In(III) ions are bridged by imidazolate (im) ligands into 3D frameworks that are related to distorted filled-ReO3 (ABX3 perovskite) structures with different octahedron tilting. Clathrate-type phases I (cubic space group Im3) and II (trigonal R3) may be formulated as [A′A″3In4(im)12] and contain two types of cubic cages, A′ and A″, which may host guest molecules and are occupied by im moieties, respectively. A reversible structural phase transition between low-temperature phase II and high-temperature phase I, occurring on heating at about 90 °C, was studied by DSC and variable-temperature powder XRD experiments. Depending on the synthesis, more specifically on the nature and amount of guests trapped in the A′ cages, the phase transition was suppressible, enabling I to be recovered at room temperature. Phase III (trigonal R3) may be formulated as [AIn(im)3]. It is a dense phase in which the cubic A cages are occupied by im moieties. For the first time, the ionothermal formation of a coordination polymer, phase III, was monitored in situ by time-resolved EDXRD experiments. Rate constants and activation energies for both nucleation and crystal growth, as estimated by kinetic analysis of the EDXRD data, are compared to corresponding values reported previously for the solvothermal crystallization of other coordination polymers.