La4Te7O20: A new ternary rare-earth Metal(III) Oxotellurate(IV) with isolated [TeO3]2– and [Te3O8]4– anions

Abstract The new-rare earth metal (III) oxotellurate (IV) La4Te7O20 was obtained as a single-crystalline by-product of the La2Te3O9 synthesis through a solid-state reaction of the corresponding binary oxides La2O3 and TeO2. The colorless, lath-shaped crystals of La4Te7O20 crystallize in the monoclinic space group C2/c with the lattice parameters a = 2740.63 (16) pm, b = 580.92 (3) pm, c = 1326.71 (8) pm and β = 106.849 (3)° for Z = 4. The structure consists of two crystallographically distinct lanthanum-oxygen polyhedra with the coordination numbers of seven plus one and eight (d (La3+–O2–) = 241–262 p.m. plus 310 p.m.). These lanthanum-oxygen polyhedra are attached to one ψ eq 1 -trigonal [TeO4]4– bipyramid (d (Te4+–O2–) = 186–214 p.m., 2 × each) and three different ψ1-[TeO3]2– tetrahedra (d (Te4+–O2–) = 184–189 p.m.) with twice the frequency of occurrence. So the central [TeO4]4– core is linked with two [TeO3]2– groups via common oxygen vertices to form an isolated [Te3O8]4– anion, leading to the structural formula La4 [Te3O8][TeO3]4. The presence of all these different oxotellurate (IV) units is confirmed by a single-crystal Raman spectrum.