Crystal structure, vibrational and thermal behavior of Ba(NH4)[Co(CN)6]·4H2O: A new precursor for the synthesis of hexagonal BaCoO3

The crystal structure of Ba(NH4)[Co(CN)6]·4H2O complex was determined by X-ray diffraction methods. It crystallizes in the hexagonal P63/m space group with a = b = 7.6882(2) Å, c = 14.4764(4) Å, and Z = 2 molecules per unit cell. The structure was solved from 475 reflections with I > 2σ(I) and refined to an agreement R1-factor of 0.0214. The cobaltocyanide anion has an octahedral shape with its Co(III) ion sited at a crystallographic special position of point symmetry bar3 (S6) [d(Co-C) = 1.886(3) Å and d(C-N) = 1.143(4) Å]. The barium ion is in a 9-fold environment at a crystal special position 6¯ (C3h), coordinated to cyanide N-atoms of neighboring complexes [d(Ba-N) = 2.862(3) Å] and to one type of water molecule laying onto an m mirror plane [d(Ba-Ow) = 2.924(4) Å]. The ammonium ion and the other type of water molecule share four symmetry-related C3 lattice sites with equal occupancy. Under the P63 subspace group these four sites split into two independent pairs of C3 sites, one occupied by two symmetry-related ammonium ions, the other by two (disordered) water molecules.