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The reaction of Lewis acidic metal halides with chalcogen tetrahalides leads to double halides of the general formula [EX 3 ][MX  n  ] (E=S, Se, Te; X=F, Cl, Br, I).  α -[TeCl 3 ][NbCl 6 ] and  α -[TeCl 3 ][TaCl 6 ] were obtained from Nb/Cl 5 /TaCl 5  and TeCl 4  in evacuated glass ampoules in a temperature gradient 423 → 403 K, [TeCl 3 ][WCl 6 ] was obtained from Te and WCl 6  with WCl 5  as by product. If the reaction of NbCl 5 /TaCl 5 , and TeCl 4  was carried out in the presence of CCl 4  a second polymorphic form  β -[TeCl 3 ][MCl 6 ] (M=Nb, Ta) crystallized. [TeBr 3 ][WBr 6 ] and [TeBr 3 ][TaBr 6 ] could only be obtained by rapid cooling of the gasphase over solid WBr 5 /TaBr 5 –TeBr 4  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 [TeX 3 ] +  and octahedral [MX 6 ] −  ions. The primary coordination sphere of the tellurium atom is completed by secondary Te–X interactions to a distorted TeX 3+3  octahedron. The differences between the crystal structures lie in the different interconnections between cations and anions. [TeCl 3 ][WCl 6 ] and  α -[TeCl 3 ][MCl 6 ] (M=Nb, Ta) are built of one-dimensional “ladder-type” connected polyhedra, the structures of  β -[TeCl 3 ][MCl 6 ] (M=Nb, Ta) consist of discrete tetranuclear units and [TeBr 3 ][MBr 6 ] (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 [EX 3 ][MX  n  ] which are all known to contain trigonal-pyramidal [EX 3 ] +  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.

zeitschrift für kristallographie - crystalline materials

Trihalogenochalcogenonium-halogenometallates [EX 3 ][MX  n  ] – Synthesis and crystal structures of [TeX 3 ][MX 6 ] (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