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- Title
Syntheses, Crystal Structures, and Twinning of the Isotypic Rare-Earth Metal Bromide Ortho-Oxidomolybdates LaBrMoO<sub>4</sub> and CeBrMoO<sub>4</sub>.
- Authors
Hartenbach, Ingo; Henning, Harald; Schleid, Thomas; Schustereit, Tanja; Strobel, Sabine
- Abstract
Solid-state reactions of La2O3, LaBr3, and MoO3 in molar ratios of 1:1:3 lead to single crystals of LaBrMoO4 among a few by-products, which emerge from redox reactions of Br- with hexavalent molybdenum. To obtain the analogous cerium compound, Ce2O3 was synthesized in situ by using CeO2 and Ce in a 3:1 molar ratio. The two rare-earth metal bromide ortho-oxidomolybdates(VI) REBrMoO4 ( RE = La and Ce) crystallize isotypically in the monoclinic space group Pc ( a = 982 - 977 pm, b ≈ 581 pm, c = 810 - 803 pm, β ≈ 90°, Z = 4). In the crystal structure, two crystallographically unique RE3+ cations are present, both with similar coordination environments of three plus one Br- and six O2- anions in the shape of distorted tetracapped trigonal prisms. The two distinguishable Br- anions both display coordination spheres of three plus one RE3+ cations each, building up distorted tetrahedra. These are fused together via four common edges to form anti-PbO-type 2∞{[Br RE $\rm^{e}_{4/4}$]2+} layers ( e = edge-connecting) parallel to the (100) plane. Two crystallographically different oxidomolybdate(VI) units are also found in the structure, which can be best described as strands of apically vertex-shared [MoO5]4- trigonal bipyramids along [001] represented by the formula 1∞{[MoO $\rm^{e}_{4/4}$O $\rm^{e}_{4/4}$]2-} ( v = vertex-connecting, t = terminal). The aforementioned 2∞{[Br RE $\rm^{e}_{4/4}$]2+} layers and the 1∞ {[MoO $\rm^{e}_{4/4}$O $\rm^{e}_{4/4}$]2-} chains are alternately stacked along the a axis. The peculiarity of this structure is expressed by the position of the Mo6+ cations, which are not situated in the center of the bipyramids, but reside offset in a trigonal pyramid. Since both the (Mo1)6+ and the (Mo2)6+ cations are located in the same partial tetrahedron, relative to the triangular plane of the trigonal bipyramid, a structure description in a non-centrosymmetric space group is immanent. Both title compounds display a twinned crystal structure with strong similarities to those of the chloride homologues REClMoO4 ( RE = La - Pr) and LaClWO4.
- Publication
Zeitschrift für Anorganische und Allgemeine Chemie, 2013, Vol 639, Issue 2, p347
- ISSN
0044-2313
- Publication type
Article
- DOI
10.1002/zaac.201200433