Unexpected Polymorphism in Bromoantimonate(III) Complexes and Its Effect on Optical Properties

Abstract

Reactions of [SbBr₆]^3- containing HBr solutions with bromide salts of 1,1'-(1,2-ethanediyl)bis(pyridine) (PyC₂²⁺) or 1,1'-(1,2-ethanediyl)bis(3,5-dimethylpyridine) (3,5-MePyC₂²⁺) initially result in the formation of the deep orange complexes Cat[SbBr₅] (<b>1</b> and <b>2</b>), featuring unusual Sb···Br interactions in the solid state. In the mother liquor, <b>1</b> transforms into discrete binuclear (C₂Py)₂[Sb₂Br₁₀], which demonstrates polymorphism (triclinic <b>3</b> and monoclinic <b>4</b>), while <b>2</b> transforms into polymeric (3,5-MePy){[SbBr₄]} (<b>5</b>). DFT calculations reveal that the system of noncovalent Sb···Br contacts may be responsible for the appearance of the observed optical properties (unusual deep orange coloring).