SYNTHESIS AND CRYSTAL-STRUCTURE OF THE FIRST ZINC-CONTAINING PYROBORATES NI1.5ZN0.5(B2O5) AND CO1.5ZN0.5(B2O5)

The first zinc containing pyroborates Ni1.5Zn0.5(B2O5) (A) and Co1.5Zn0.5(B2O5) (B) were prepared by using a (B)2O(3) flux technique. Single crystals were investigated by X-ray diffraction and showed triclinic symmetry, space group C-i(1)-P (1) over bar. The structures are isotypic to Co-2(B2O5) with the lattice parameters (A) a = 331.28(6), b = 613.87(11), c = 922.2(2), alpha = 104.067(11)degrees, beta = 90.672(13)degrees, gamma = 92.413(12)degrees and (B) a = 315.89(2), b = 612.84(6), c = 997.72(6), alpha = 104.103(7)degrees, beta = 91.020(6)degrees, gamma = 92.540(7)degrees, Z = 2. All metal point positions show an octahedral oxygen coordination and a partly statistical distribution of Zn2+ and Ni2+ or Co2+, respectively. Isolated nearly planar B2O5 units connect ribbons consisting of edge sharing metal octahedra.