Helical chains of [MO5Cl] octahedra – Three compounds in the new family AEM2Te3O8Cl2 (AE = Ca, Sr and M = Co, Ni)

The compounds CaCo2Te3O8Cl2, SrCo2Te3O8Cl2 and SrNi2Te3O8Cl2 were synthesized via solid–gas reactions and investigated using single-crystal X-ray diffraction. While the compound CaCo2Te3O8Cl2 formed large enough single crystals to allow for a detailed structural analysis, crystals of the Sr-containing compounds yielded evidence that they are isostructural. CaCo2Te3O8Cl2 crystallizes in the monoclinic system, space group P21/c, a = 6.537(2) Å, b = 9.088(2) Å, c = 19.500(9) Å, β = 113.36(4)°, Z = 4. It exhibits [CoO5Cl] helical chains along the [010] direction, connected by [CaO8] polyhedra, [TeO3E] tetrahedra and [TeO4E] trigonal bipyramids (the lone pair of electrons on TeIV is designated as E) to form a layer. The layers are held together only by weak van der Waals forces; the shortest interlayer distance is a Te⋯Cl contact of 3.432(4) Å.

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