δ-La(BO2)3 (≡δ-LaB3O6): A new high-pressure modification of lanthanum meta-oxoborate

The δ modification of lanthanum meta-oxoborate was discovered during our systematic investigations in the field of oxoborates, synthesized under high-pressure conditions. δ-La(BO2)3 (≡δ-LaB3O6) was obtained at high-pressure (5.5 GPa) and high-temperature (1050 °C) in a Walker  -type multianvil apparatus. The monoclinic compound crystallizes with four formula units in the space group P21/cP21/c, exhibiting lattice parameters of a=424.1(1)a=424.1(1), b=1171.2(2)b=1171.2(2), c=731.1(2) pmc=731.1(2) pm, and β=91.2(1)°β=91.2(1)°. Due to the synthesis under high-pressure conditions, the structure exhibits [BO4]5− tetrahedra exclusively, which are connected via common corners. Additionally, 1/6 of the oxygen atoms are bridging three boron atoms (O[3]), leading to a network structure with ten-membered rings of [BO4]5− tetrahedra (d(BO)=144–155 pmd(BO)=144–155 pm), in which the La3+ ions are coordinated by twelve oxygen atoms (d(LaO)=245–332 pmd(LaO)=245–332 pm). After a discussion of the structure, infrared and temperature-dependent X-ray powder diffraction data are presented.

Figure optionsDownload as PowerPoint slide