Synthesis and Crystal Structure of the Acentric Indium Borate InB6O9(OH)3

Al5B12O25(OH) and Ga4InB12O25(OH) – two additional triel borates with the structure type M 5B12O25(OH) (M = Ga, In)

The isotypic triel borates Al5B12O25(OH) and Ga4InB12O25(OH) were synthesized in a Walker-type multianvil apparatus under high-pressure/high-temperature conditions of 12.0 GPa/1400 °C and 12.3 GPa/1200 °C, respectively. The crystal structures of both compounds, determined by single-crystal X-ray diffraction, constitute new representatives of the structure type M 5B12O25(OH) (M = Ga, In) crystallizing in the space group I41/acd. The presence of the hydroxyl groups was confirmed via single-crystal IR spectroscopy.

High-pressure synthesis and characterization of the non-centrosymmetric scandium borate ScB6O9(OH)3

The non-centrosymmetric scandium borate ScB6O9(OH)3 was obtained through a high-pressure/high-temperature experiment at 6 GPa and 1473 K. Single-crystal X-ray diffraction revealed that the structure is isotypic to InB6O9(OH)3 containing borate triple layers separated by scandium layers. The compound crystallizes in the space group Fdd2 with the lattice parameters a = 38.935(4), b = 4.4136(4), and c = 7.6342(6) Å. Powder X-ray diffraction and vibrational spectroscopy were used to further characterize the compound and verify the proposed structure solution.

M4LiBe4P7O24 and M4Li(Li3P)P7O24 (M = Cs, Rb): deep-ultraviolet nonlinear-optical phosphates with a tetrahedra-substituted paracelsian-like framework

Paracelsian-like beryllophosphates M₄LiBe₄P₇O₂₄ and tetrahedra-substituted phases M₄Li(Li₃P)P₇O₂₄ (M = Cs, Rb) undergo structural transformation originating from the nature of tetrahedral cations.

High-pressure synthesis and crystal structure of the mixed-cation borate Ga4In4B15O33(OH)3

The mixed cation triel borate Ga4In4B15O33(OH)3 was synthesized in a Walker-type multianvil apparatus at high-pressure/high-temperature conditions of 12.5 GPa and 1300°C. Although the product could not be reproduced in further experiments, its crystal structure could be reliably determined via single-crystal X-ray diffraction data. Ga4In4B15O33(OH)3 crystallizes in the tetragonal space group I41/a (origin choice 2) with the lattice parameters a = 11.382(2), c = 15.244(2) Å, and V = 1974.9(4) Å3. The structure of the quaternary triel borate consists of a complex network of BO4 tetrahedra, edge-sharing InO6 octahedra in dinuclear units, and very dense edge-sharing GaO6 octahedra in tetranuclear units.

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

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.

Exploration into the Syntheses of Gallium- and Indiumborates under Extreme Conditions: M5 B12 O25 (OH): Structure, Luminescence, and Surprising Photocatalytic Properties

Explorative solid-state chemistry led to the discovery of the two new compounds Ga₅ B₁₂ O₂₅ (OH) and In₅ B₁₂ O₂₅ (OH). Extreme synthetic conditions within the range of 12 GPa and a temperature of 1450 °C realized in a Walker-type multianvil apparatus resulted in the formation of an unprecedented tetragonal structure with the exclusive presence of condensed BO₄ tetrahedra, forming cuboctahedral cavities. Doping of these cavities with Eu³⁺ in In₅ B₁₂ O₂₅ (OH) yielded in an orange-red luminescence. Photocatalytic tests of In₅ B₁₂ O₂₅ (OH) revealed a hydrogen production rate comparable to TiO₂ but completely co-catalyst free.