Crystal Structures and Twinning of RuBr3.

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 R3‾ ${\bar{3}}$). 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. [ABSTRACT FROM AUTHOR]