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

Reactions of [SbBr6]3– containing HBr solutions with bromide salts of 1,1′-(1,2-ethanediyl)­bis­(pyridine) (PyC2 2+) or 1,1′-(1,2-ethanediyl)­bis­(3,5-dimethylpyridine) (3,5-MePyC2 2+) initially result in the formation of the deep orange complexes Cat­[SbBr5] (1 and 2), featuring unusual Sb···Br interactions in the solid state. In the mother liquor, 1 transforms into discrete binuclear (C2Py)2[Sb2Br10], which demonstrates polymorphism (triclinic 3 and monoclinic 4), while 2 transforms into polymeric (3,5-MePy)­{[SbBr4]} (5). 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).