Synthese und Kristallstruktur des Holmium(III)-chlorid-oxotellurats(IV) HoClTeO₃

Synthesis and Crystal Structure of the Holmium(III) Chloride Oxotellurate(IV) HoClTeO₃

Orange coloured, rod—shaped single crystals of the holmium( III) chloride oxotellurate(IV) HoClTeO₃ (orthorhombic, Pnma; a = 730.25(5), b = 696.54(5), c = 905.18(7) pm; Z = 4) are obtained during attempts to synthesize holmium(III) oxochlorotellurates(IV) by reaction of holmium oxychloride (HoOCl) and tellurium dioxide (TeO₂; 1:1—2molar ratio, 800 °C, 40 d) in evacuated silica tubes. The crystal structure contains sevenfold coordinated Ho ³⁺ cations surrounded by five oxide and two chloride anions forming a pentagonal bipyramid. Interconnection of the [Ho(O1)(O2)₄Cl₂] polyhedra occurs via two edges made of four equatorial oxygen atoms (O2) under formation of {[Ho(O1)(O2)_4/2Cl_2/1]^5-} chains running parallel [010]. These arrange as hexagonal closest packing of rods and are linked to each other by Cl^- anions to a three—dimensional {[Ho(O1)_1/1(O2)_4/2Cl_2/2]^4-} network. All Te⁴⁺ cations are embedded therein and exhibit ψ¹—tetrahedral coordination figures as discrete anionic [Te(O1)(O2)₂]^2- pyramids due to the stereochemical activity of the non—binding electron pairs („lone pairs”︁). They stabilize the {[HoO₃Cl]^4-} network via covalent bonds to one axial (O1) and two equatorial oxygen atoms (O2) of each [HoO₅Cl₂] polyhedron.