Methylviologen Bromobismuthates

New methylviologen (MV2+) bromobismuthate [MV]3[BiBr6]2 · 2H2O (I) isostructural to the well-known chlorobismuthate [MV]3[BiCl6]2 · 2H2O has been prepared from an aqueous solution and cha-racterized by X-ray diffraction. The reaction between I and concentrated HBr leads to the formation of acidic methylviologen bromobismuthate-bromide [H3O]2[MV][BiBr6]Br · 4H2O (II) and a minor impurity of bromobismuthate tribromide [MV]3[Bi2Br9][Br3]3 (III). The acidic bromobismuthate of ethylviologen (EtV2+) [H3O][EtV][BiBr6] · 1.34H2O (IV) formed under similar conditions has another composition. Thermal decomposition of II yields single-phase [MV][BiBr5], which has a low optical band gap. The electrochemical characteristics of I and related iodobismuthate [MV]3[Bi2I11]I have been compared.