Synthesis and crystal structure of BaZn(CO_3)F_2; revision of the structure of BaMn(CO_3)F_2

摘要

The synthesis and the crystal structure of two isostructural fluoride carbonates are presented. BaZn(CO_3)F_2 and BaMn(CO_3)F_2, obtained by hydrothermal growth (T = 650 ℃, P = 210 MPa, t = 48 h), are hexagonal, P6_3/m, Z = 2, with a = 4.8523(8), c = 9.854(1) A for BaZn(CO_3)F_2 and a = 4.9120(8), c = 9.919(1) A for BaMn(CO_3)F_2. Their structures are solved by X-ray diffraction; the reliability factors are R/R_W = 0.016/0.039 and R/R_W = 0.019/0.046 for BaZn(CO_3)F_2 and BaMn(CO_3)F_2, respectively. The 3D network is built up from [MO_3F_2] (M = Zn, Mn) polyhedra and CO_3~(2-) groups, which lie in (0001) planes. The structures, which derive from the structure of KPu(CO_3)O_2, are very similar to the structures of two fluoride borates. BaAl(BO_3)F_2 and BaGa(BO_3)F_2, recently published.