Ho11ClTe16O48: Ein extrem chlorarmes Chlorid-Oxotellurat(IV) des dreiwertigen Holmiums

Ho11ClTe16O48: An Extremly Chlorine-Poor Chloride Oxotellurate(IV) of Trivalent Holmium While attempting to synthesize Ho2Te3O9 by reacting Ho2O3 with TeO2 (800 °C, 12 d) chloride from the CsCl flux was incidently mobilized and as by-product, Ho11ClTe16O48 (triclinic, ; a = 551.52(3), b = 1193.54(6), c = 1834.63(9) pm, α = 100.814(3), β = 95.443(3), γ = 100.175(3)°; Z = 1), the first example of this new composition in the field of lanthanoid(III) chloride oxotellurates(IV) has been obtained. The six crystallographically different Ho3+ cations experience a six-, seven- and eightfold coordination through oxygen atoms (d(Ho3+−O2−) = 221 – 280 pm), leading to octahedral, triangle-square polyhedral, capped trigonal prismatic and square antiprismatic coordination figures. Initially, the corresponding [HoOn] polyhedra convene to layers parallel to the (001) plane via edge and corner sharing which again combine to a [Ho11O48]63− network via other individual [(Ho6)O6] octahedra and [(Ho2)2O4/2O4/1] chains along [100], whose three-dimensional characteristic is unique among the lanthanoid(III) oxotellurates(IV) known to date. The eight crystallographically independent Te4+ cations exhibit coordination numbers of 3 and 3+1 in relation to oxygen, except Te1 with 3+1 O2−plus 1 Cl− as anionic neighbours. Apart from isolated [TeO3]2− polyhedra (Ψ1 tetrahedra: d(Te4+−O2−) = 184 – 196 pm) only double and triple groupings occur even in considering secondary Te4+···O2− contacts (d′(Te4+···O2−) = 218 – 264 pm). As with HoCl[TeO3], the tellurium-oxygen partial structure does not get beyond a “zero-dimensional” expression. The Te4+ cations adjust so well while lining the empty cavities within the network, that still only two Te4+-decorated channel types (oval and round) remain unoccupied, offering space for the non-bonding electron pairs (“lone pairs”). The Cl− anions reside in the bigger oval channels (d(Cl−−Te4+) = 286, 352 and 358 pm, 2 × each). In the default of binding Ho3+−Cl− contacts, the correct description of this new compound would thus be holmium(III) oxochlorotellurate(IV) Ho11[Te16O48Cl] according to Ho11[TeO3]2[Te2O6]2[Te3O9]2{Cl[Te2O6]2}. The presence of chloride was not only detected by the structure refinement on the basis of X-ray diffraction data, but also even in such small quantities by elementary analysis with the electron-beam microprobe.