Crystal Structures and Twinning of RuBr₃

Abstract

The concerted experimental and computational study reports on the polymorphic behavior of RuBr₃. Highly‐resolved X‐ray powder diffraction measurements of the modification lt‐RuBr₃ give direct evidence for peak splitting substantiating an orthorhombic unit cell with additional weak intensities confirming a primitive lattice. The crystal structure of lt‐RuBr₃ is determined using the intensities of a “Drilling” individuum. For lt‐RuBr₃, findings of density functional theory calculations suggest that the deviation from hexagonal symmetry is mainly driven by electronic correlations. Reinvestigation of the recently reported high‐pressure modification hp‐RuBr₃ essentially confirms the rhombohedral BiI₃‐type crystal structure (space group R ). Simulations of the atomic arrangement of hp‐RuBr₃ indicate that spin‐orbit coupling and corrections for the van‐der‐Waals dispersive forces are mandatory to reach a reasonable agreement with the experimentally determined crystal structure.