A New Transition Metal Borate, Co₆(B₂₄O₃₉(Oh)₆(H₂O) ₆·2.21H₂O, Synthesized via a Mild Hydrothermal Synthesis

A new transition metal borate hydrate, Co6B24O39(OH)6(H2O)6·2.21H2O, was synthesized via a mild hydrothermal method using boric acid as the melt. The compound crystallizes in the trigonal space group P 3‾ with lattice parameters a = b = 13.17840(10) Å, c = 12.3287(2) Å, and a unit cell volume of 1854.27(4) Å3 (Z = 2). This borate hydrate crystallizes in a new structure type comprised of layers containing [BO3] trigonal planar units and [BO4] tetrahedra that are linked by CoO6 and Co(OH)2(H2O)4 octahedra via corner-sharing. The crystalline phase was confirmed by powder X-ray diffraction, while single-crystal X-ray diffraction was used to determine the structure. The structure contains eight crystallographically independent boron atoms that connect to each other and form a Fundamental Building Block (FBB) consisting of two triborate rings [B3O7OH] and two [BO3] trigonal planar units connected via corner-sharing. This FBB can be written as 8: ∞2[2(3:Δ + 2T) + 2(1:Δ)]. Optical and magnetic measurements, as well as thermal analyss, were carried out to characterize the new borate.