High-pressure syntheses and characterization of the transition metal borates β-MB4O7 (M = Mn2+, Ni2+, Cu2+)

In this work, we report about the synthesis of the borates β-MnB4O7, β-NiB4O7, and β-CuB4O7 under high-pressure/high-temperature conditions. Starting reagents were molar mixtures of boron oxide and the corresponding metal oxide (MnO2, NiO, CuO), which were transformed at 7.5 GPa to the borates β-MB4O7 (M = Mn, Ni, Cu) at temperatures of 1000, 1150, and 550 °C, respectively. The single crystal structure determinations of all three compounds revealed isotypy to β-ZnB4O7, crystallizing in the space group Cmcm with Z = 4; β-MnB4O7: a = 1088.5(2), b = 663.3(2), c = 518.7(2) pm, R1 = 0.0209, wR2 = 0.0553 (all data); β-NiB4O7: a = 1087.5(2), b = 636.8(2), c = 518.0(2) pm, R1 = 0.0544, wR2 = 0.0894 (all data); β-CuB4O7: a = 1082.0(2), b = 646.3(2), c = 512.0(2) pm, R1 = 0.0508, wR2 = 0.0882 (all data). The structures exclusively consist of BO4 tetrahedra, which form a network with channels of four- and six-membered rings. Similarities and differences of the phases β-MB4O7 (M = Mn, Ni, Cu) are discussed in comparison to β-ZnB4O7. Furthermore, we report about magnetic, spectroscopic, and thermal investigations.

The new borates β-MnB4O7, β-NiB4O7, and β-CuB4O7 were synthesized under high-pressure/high-temperature conditions.Figure optionsDownload as PowerPoint slide