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

Reactions of SbBr63– 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 CatSbBr5 (1 and 2), featuring unusual Sb···Br interactions in the solid state. In the mother liquor, 1 transforms into discrete binuclear (C2Py) 2Sb2Br10, 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).