Synthesis and Crystal Structure of the High-pressure Cobalt Borate HP-CoB₂O₄

The cobalt borate HP-CoB 2 O4 was synthesized from Co 3 O 4 and B 2 O 3 under high-pressure / high-temperature conditions of 6.5 GPa and 950 °C. The structure of HP-CoB 2 O 4 is isotypic to HPNiB 2 O 4 and β -FeB 2 O 4 , representing the third example of a borate, in which every BO 4 tetrahedron shares a common edge with a second one. HP-CoB 2 O 4 crystallizes in the space group C2/c (Z = 4) with the parameters a = 934.6(2), b = 562.0(2), c = 443.3(1) pm, β = 108.2(1)°, V = 0.2212(1) nm 3 , R 1 = 0.0218, and wR 2 = 0.0410 (all data). The structure consists of layers of BO 4 tetrahedra, that are interconnected via strings of edge-sharing FeO 6 octahedra