Syntheses and Crystal Structures of the Bromide-derivatized Lanthanoid(III) Ortho-Oxomolybdates(VI) LnBr[MoO4] (Ln = Pr, Nd, Sm, Gd

The lanthanoid(III) bromide ortho-oxomolybdates(VI) LnBr[MoO₄] (Ln = Pr, Nd, Sm, Gd–Lu) crystallize triclinically in the space group P1̅ (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 Ln³⁺ 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). Furthermore, the common structure of the LnBr[MoO₄] series contains two crystallographically different, discrete [MoO₄]²⁻ ortho-oxomolybdate(VI) tetrahedra. Two plus one oxygen atoms of each [(Mo1)O₄]²⁻ unit are used to interconnect the polyhedra around (Ln1)³⁺ and (Ln2)³⁺ together with one Br⁻ anion (Br2). The connection between two polyhedra around (Ln2)³⁺ is generated exclusively by two plus one oxygen atoms of two [(Mo2)O₄]²⁻ anions. The complete structural arrangement can be considered as a bundle of primitively packed _∞¹{LnBr[MoO₄]} chains with two alternating motifs of linkage, which are running parallel along [012].