Abstract
Reaction of chromium(III) precursors with TeO2 in PbF2/PbO melts in air led to oxidation of chromium(III) to chromium(VI), whereas tellurium remained its oxidation state of IV. In the resulting title compound, Pb2(CrO4)(TeO3), the two types of anions are isolated from each other, hence a double salt is formed. The two independent Pb2+ cations exhibit coordination number nine under formation of very distorted coordination polyhedra [bond-length range = 2.363 (6)-3.276 (7) Å]. The oxochromate(VI) and oxotellurate(IV) anions have tetra-hedral and trigonal-pyramidal configurations, respectively. In the crystal structure, (001) layers of metal cations alternate with layers of TeO32- and CrO42- anions along [001], forming a three-dimensional framework structure. Pb2(CrO4)(TeO3) is isotypic with its sulfate analogue Pb2(SO4)(TeO3) and is comparatively discussed.
Highlights
Reaction of chromium(III) precursors with TeO2 in PbF2/PbO melts in air led to oxidation of chromium(III) to chromium(VI), whereas tellurium remained its oxidation state of IV
If only Pb—O bond lengths < 2.8 Å are considered, atom Pb1 is surrounded by six O atoms in the range 2.4–2.8 Å whereas atom Pb2 has four oxygen atoms as coordination partners, three at 2.38 Å and one at 2.75 Å
The Pb2+ cations are arranged in layers parallel to (001) at z 0, 12 and in turn are stacked into columns extending along [010]
Summary
Pb3Fe2Te2O12 is an oxotellurate(VI) with interesting structural features. It crystallizes in the non-centrosymmetric space group Cc and has TeVI and FeIII atoms occupationally disordered at the same sites (Müller-Buschbaum & Wedel, 1997). This compound has been prepared by solid-state reactions from a PbO, Fe2O3 and TeO2 mixture in air, which led to oxidation of TeIV to TeVI. During an attempt to replace iron(III) by chromium(III) to prepare a possible phase with composition ‘Pb3Cr2Te2O12’, the title compound, Pb2(CrO4)(TeO3), was obtained instead while working under similar conditions. CrVI) while tellurium remained its oxidation state of IV. Pb2(SO4)(TeO3) (Weil & Shirkhanlou, 2017)
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