High‐Pressure Synthesis of the Acentric Borate DyB₅O₈(OH)₂

Abstract

The novel dysprosium borate DyB 5 O 8 (OH) 2 was synthesized in a Walker-type multianvil apparatus at a pressure of 2.5 GPa and a temperature of 673 K. Single-crystal diffraction data provided the basis for the structure solution and refinement. The compound crystallizes in the acentric monoclinic space group C2 (no. 5) with the lattice parameters a = 7.9288(5), b = 4.4009(3), c = 9.3409(8) Å, and a monoclinic angle of IntroductionRare earth oxoborates include a wide variety of structural motifs with several different structures. One focus of our intensive research is the synthesis of novel rare earth oxoborates possessing anionic backbones as highly condensed as possible. In the case of borate structures exclusively built up from [BO 4 ] 5tetrahedra, an increase in the B/O ratio coincides with a higher degree of condensation. This concept is derived from the general concept of condensation found in silicates. [1] The dominant structural motive found in high-pressure borates are [BO 4 ] 5tetrahedra, which is in contrast to borates synthesized under ambient pressure conditions, where the [BO 3 ] 3group dominates. Our research has already yielded several examples of highly condensed borates like YB 7 O 12 , [2] -Eu(BO 2 ) 3 , [3] or Dy 4 B 6 O 15 . [4] Especially, the dysprosium borates comprise a variety of different structural motifs incorporating [BO 3 ] 3and [BO 4 ] 5groups and the linkage of these groups to a variety of polyanions. With Dy 4 B 6 O 15 , the first oxoborate with edge-sharing [BO 4 ] 5tetrahedra was found under high-pressure/high-temperature conditions, which was one of the most interesting results, because this structural feature was completely unknown, before we started our investigations under such extreme conditions. Subsequently, the research effort in the multianvil apparatus yielded phases like /ν-DyBO 3 , [5][6] α/ -Dy 2 B 4 O 9 , [7][8] [a]