High-pressure Synthesis and Characterization of the Rare-earth Borate La 4 B 10 O 21

Dedicated to Professor Wolfgang Beck on the occasion of his 80 th birthday The lanthanum(III)-decaborate La 4 B 10 O 21 was synthesized under high-pressure/high-temperature conditions of 2.6 GPa and 750 ◦C in a Walker-type multianvil apparatus. The single-crystal structure determination revealed that La 4 B 10 O 21 is isotypic to Pr 4 B 10 O 21 . La 4 B 10 O 21 crystallizes monoclinically with four formula units in the space group P2 1 / n with the lattice parameters a = 716.7(2), b = 1971.5(4), c = 958.3(2) pm, and β = 93.7(1)◦. The three-dimensional boron-oxygen framework consists of [BO 4 ] 5− tetrahedra and trigonal-planar [BO 3 ] 3− groups. The structure contains four crystallographically different lanthanum ions. Two of the ions are surrounded by 10, one by 11, and the fourth one by 12 oxygen anions. In addition to IR-spectroscopic investigations, DFT calculations were performed to support the assignment of vibrational bands.