The First High‐Pressure Chromium Oxonitridoborate CrB(4)O(6)N—an Unexpected Link to Nitridosilicate Chemistry

CrB(4)O(6)N crystallizes in the non‐centrosymmetric space group P6(3) mc (no. 186) with the lattice parameters a=5.1036(1), c=8.3519(3) Å, and a volume of 188.40(1) Å(3). It was synthesized in a high‐pressure/high‐temperature experiment at 7 GPa and 1673 K and represents the first high‐pressure oxonitridoborate. It is built up of starlike‐shaped entities of four BO(3)N tetrahedra, connected via one common nitrogen atom that resembles the fourfold‐coordinated nitrogen atoms in the homeotypic nitridosilicates MYbSi(4)N(7) (M=Sr, Ba). Building up a network with channels that contain the Cr(3+) ions, CrB(4)O(6)N contains for the first time a tetrahedral building unit in contrast to trigonal planar B(O/N)(3) entities in all other known oxonitridoborates. The structural relations as well as the results of spectroscopic measurements and calculations on the chromium oxonitridoborate are discussed.