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∞{[BrRE$\rm^{e}_{4/4}$]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∞{[BrRE$\rm^{e}_{4/4}$]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.

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Red, transparent single crystals of molybdenum(VI) dioxide dibromide MoO 2 Br 2 emerged as by-product after thermal analyses of reaction mixtures comprising REBr 3 (RE = La or Gd) and MoO 3 . The structure of this highly water sensitive compound can be described in the non-centrosymmetric monoclinic space group Cc with the lattice constants a = 1522.33 (15) pm, b = 390.61(4) pm, c = 771.09(8) pm, β = 104.394(7)°and four formula units per unit cell. Crystallographically unique Mo 6+ cations are surrounded by four oxide and two * Dr. I. Hartenbach

The lanthanoid(III) bromide ortho-oxomolybdates(VI) LnBr [MoO 4 ] (Ln = Pr, Nd, Sm, Gd -Lu) crystallize triclinically in the space group P1 (a = 686 -689, b = 713 -741, c = 1066 -1121 pm, α = 103 -106, β = 107 -108, γ = 92 -95 • ) with Z = 4. The crystal structure contains two crystallographically distinguishable Ln 3+ cations, each one with a coordination number of seven plus one. (Ln1) 3+ is surrounded by three bromide and four plus one oxide anions, while for (Ln2) 3+ just one bromide and six plus one oxide anions belong to the coordination sphere. Considering the smallest lanthanoids, however, the distances to the farthest anions increase so much that their contribution to the coordination spheres becomes negligible in both cases. The polyhedra around (Ln1) 3+ are connected to each other via common edges, which consist of two crystallographically identical Br − anions (Br1).