Trihalogenochalcogenonium-halogenometallates [EX3][MX n ] – Synthesis and crystal structures of [TeX3][MX6] (X=Cl, Br; M=W, Nb, Ta) and a suggestion for a structure designation code for the various structure types in this family of compounds

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Abstract The reaction of Lewis acidic metal halides with chalcogen tetrahalides leads to double halides of the general formula [EX3][MX n ] (E=S, Se, Te; X=F, Cl, Br, I). α-[TeCl3][NbCl6] and α-[TeCl3][TaCl6] were obtained from Nb/Cl5/TaCl5 and TeCl4 in evacuated glass ampoules in a temperature gradient 423 → 403 K, [TeCl3][WCl6] was obtained from Te and WCl6 with WCl5 as by product. If the reaction of NbCl5/TaCl5, and TeCl4 was carried out in the presence of CCl4 a second polymorphic form β-[TeCl3][MCl6] (M=Nb, Ta) crystallized. [TeBr3][WBr6] and [TeBr3][TaBr6] could only be obtained by rapid cooling of the gasphase over solid WBr5/TaBr5–TeBr4 mixtures from 453 K to room temperature as orange colored crystals in low yields. The structures of the seven compounds have been determined by single crystal X-ray diffraction. All of them consist of trigonal-pyramidal [TeX3]+ and octahedral [MX6]− ions. The primary coordination sphere of the tellurium atom is completed by secondary Te–X interactions to a distorted TeX3+3 octahedron. The differences between the crystal structures lie in the different interconnections between cations and anions. [TeCl3][WCl6] and α-[TeCl3][MCl6] (M=Nb, Ta) are built of one-dimensional “ladder-type” connected polyhedra, the structures of β-[TeCl3][MCl6] (M=Nb, Ta) consist of discrete tetranuclear units and [TeBr3][MBr6] (M=W, Ta) are made up of face sharing double octahedral molecular units. Since there are several dozen representatives in the class of chalcogenonium-halogenometallates [EX3][MX n ] which are all known to contain trigonal-pyramidal [EX3]+ cations and tetrahedral, square-planar or octahedral anions a suggestion for a simplifying general structure designation code has been developed. The code gives the number of bridging halogen atoms of each anion, the number of connected cations and a ring index for the interconnection between the ions. The code is generally applicable and was assigned to more than 40 compounds of this class with the result that only a limited number of motifs of interconnections are realized.