Mg1-xRhB - A new boridometallide with 2D polyanion

A new magnesium boridometallide Mg_1−xRhB has been prepared by reaction of the elements in an argon‐filled sealed Ta container at 1323 K. A narrow homogeneity range (0.05 ≤ × ≤ 0.08) was established by X‐ray powder diffraction data and EDXS investigations. The crystal structure of Mg_1−xRhB (x = 0.05) was solved using single‐crystal X‐ray diffraction data and confirmed by electron diffraction and high‐resolution electron microscopy (space group P6₂22, a = 5.2394(1), c = 9.4251(3) Å, Z = 6, 228 reflections, 19 variables, R(F) = 0.025). The structure can be topologically described as a derivative of the CeCo₃B₂ structure type where the positions in the cobalt layers are occupied by magnesium and rhodium atoms in an ordered manner. From the bonding analysis using the electron localization function, Mg_1−xRhB is described as a two‐dimensional [RhB] polyanion with embedded magnesium cations. The material is weakly diamagnetic and reveals metallic electrical conductivity.