Litharge-derived compounds structurally based on layers of Cl− and Br−-centered tetrahedra: Synthesis and structures of the new representatives of MX(ReO4) family (M=Ba, Pb; X=Cl, Br)

Two new layered barium perrhenate halides, BaX(ReO4) (X = Cl and Br), were prepared and their structures were refined from single-crystal and powder data, respectively. Both compounds are isostructural to the previously reported BaCl(MnO4), exhibiting a matlockite (PbFCl)-derived motif. The structure of previously reported PbBr(ReO4) was also refined, in order to obtain a complete data set; it is similar to PbCl(ReO4). The structures of Ba and Pb compounds correspond to the centro- and non-centrosymmetric versions (pseudo-polymorphs) of the same motif corresponding to the alternation of [M2X2]2+ litharge-derived slabs and double sheets of perrhenate anions. Strong relationships exist to the structures of LnX(TO4) (X = Cl, Br; T = Mo, W) which are monoclinically distorted versions of the orthorhombic permanganates and perrhenates. Crystal chemistry and further perspectives of the compounds with litharge slabs constructed of Cl, Br, and I-centered tetrahedra are discussed.