Тернарні галогеніди A3B2C9: кристалохімічні особливості, залежність деяких властивостей від середніх значень зарядів атомних ядер

Abstract

From the relevant literature data on inorganic structural chemistry, and based on the experimental results obtained in the Department of Inorganic Chemistry of the Uzhhorod National University for last three decades, the family of the A3B2C9 (A – K, Rb, Cs; B – As, Sb, Bi; C – Cl, Br, I) ternary halides has been analyzed and classified. It was shown that all halides of the above type crystallize in one of the four possible structural families, the family of Cs3Bi2Br9 (with its low-symmetry analogs), Cs3Cr2Cl9 (with its low-symmetry analogs), Cs3Bi2Cl9 or Cs3Tl2Cl9. Every structural family mentioned above is characterized by the same type of stacking of the {AC3} layers and by the same connection of the [BC6] coordination octahedra. However, all the above A3B2C9 (A – K, Rb, Cs; B – As, Sb, Bi; C – Cl, Br, I) ternary halides have also the common structural features: the closest packing of the A and C atoms, and the B atoms occupying two-thirds of the octahedral holes formed by the close-packed C halogen atoms. The most relevant crystallochemical factors (i.e. the relationship between the values of the effective ionic radii of the constituent particles and polarization-related properties of atom/ions) leading to realization of one or another structure type of the A3B2C9 halides have been discussed. Additionally, the crystallochemical peculiarities of the above A3B2C9 ternary halides, along with some their physico-chemical and physical properties (namely, melting point TM and band gap E), have been analyzed with respect to the values of the average nuclear charges. It has been established that, to certain extent, these values demonstrate correlation, which can be used for predicting purposes and for searching and development of the materials with the optimum parameters. Since the approach used in this study is quite simple and straightforward, it can be recommended for routine investigations of inorganic materials belonging to the same array of chemically and structurally similar compounds.