(NH4)InB8O14 – a high-pressure borate combining BO3 groups with corner- and edge-sharing BO4 tetrahedra

Abstract

Abstract The first ammonium indium borate (NH4)InB8O14 was synthesized from indium oxide and boric acid under high-pressure/high-temperature conditions of 9 GPa and 1000°C with a Walker-type multianvil apparatus in a BN crucible. Although a reproduction of this synthesis product failed until now, we were able to determine the crystal structure via single-crystal X-ray diffraction data collected at room temperature. (NH4)InB8O14 crystallizes in the monoclinic space group P2/m (Z=2) with a=4.4053(2), b=7.8184(3), c=12.4685(4) Å, β=94.60(1)°, and V=428.06(3) Å3. The structure comprises all three basic structural units of borates, namely corner-sharing BO4 tetrahedra, edge-sharing BO4 tetrahedra, and planar BO3 groups. Large cavities in the borate network give space to disordered, isolated ammonium ions. The presence of nitrogen (confirmed by EDX analysis) appears to originate from the container material.