A review of the structural chemistry and physical properties of metal chalcogenide halides

Given the collaborative effect between different anions, compounds containing two types of anions can have improved physical performance compared with some aspects of those containing only one type of anion. To date, many such compounds have been investigated. This review focuses on metal chalcogenide halides, namely, M-Q-X (M = metal element; Q = S, Se, Te; X = F, Cl, Br, I) compounds. Although they have similar atomic radii, chalcogen atoms have much smaller electronegativities than those of its neighboring halogen atoms, which results in their different bonding styles. The inclusion of X− into chalcogenides can move their optical band gaps to higher values and their coordination polyhedra can become more distorted, albeit with little density change. These structural effects make metal chalcogenide halides a good choice to fine-tune the structures and physical properties of chalcogenides or halides. Several hundreds of metal chalcogenide halides already have been discovered. They demonstrate rich structures and versatile physical properties, enabling their diverse applications in the fields of solid-state electrolytes, second-order non-linear optics and thermoelectricity. Considering their flourishing development, this paper provides an overview of recent achievements in the structural chemistry and physical properties of metal chalcogenide halides.