Abstract
Crystal-chemical analysis of the structures of metal (other than REE) dichalcogenides of composition X:M = 2:1 has been carried out. It is shown that there are two types of structure depending on the formal degree of metal oxidation. The first group are compounds M(X2) containing metals in the oxidation state 2+ and covalently bonded pairs of chalcogen elements; the main structural types here are cubic (pyrite) and orthorhombic (marcasite) FeS2. The second group involves the compounds MX2 with metals in the formal oxidation state 4+ and chalcogenide ions X 2 - ; the main structural types in this group are CdI2, CdCl2, MoS2. The bond lengths M–X, X–X, and X...X are analyzed; it is shown that the high polarizability of the chalcogenide ions is reflected in shortened X...X distances. In the covalently bonded pairs X–X, the bond lengths change within the following limits: 2.03-2.30, 2.35-2.55, and 2.70-2.83 A for X...X ion contacts, the minimal values are 3.07, 3.10, and 3.20 A (X = S, Se, and Te, respectively).
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