Structural and photophysical properties of octahedral metal cluster-based inorganic–organic hybrid crystals

Abstract

Inorganic–organic hybrid crystals consisting of octahedral metal clusters (MCs) are a unique class of materials for the development of photofunctional systems. However, their intrinsic structural and electronic properties have remained elusive due to the persistent presence of impurities and the challenges associated with high-purity synthesis. This review summarizes comprehensive studies focusing on high-purity synthesis, electronic characterization, and structural dynamics of MC-based compounds using a combination of experimental and theoretical approaches. The review highlights key findings, starting with the investigation of ligand-dependent electronic states via photoelectron spectroscopy and first-principles density functional theory calculations. Significant emphasis is placed on the identification of impurity phases and the development of effective purification strategies; specifically, alcohol-mediated refluxing facilely removes lattice-bound solvent molecules, thereby enhancing photoluminescence efficiency. Furthermore, this review discusses the discovery of unique lattice behaviors, including re-entrant phase transitions and structural disorder induced by lattice-bound guest molecules. Collectively, these findings establish a foundation for understanding the structures and properties of MC-based compounds and provide critical insights for fully realizing the potential of these compounds in optoelectronic applications.