Halobismuthates with halopyridinium cations: appearance or non-appearance of unusual colouring

A series of chloro- and bromobismuthate complexes with bromopyridinium cations was prepared and characterized by XRD analysis and diffuse reflectance spectroscopy. In one case, short ClBr contacts between 2-BrPyH+ and chlorobismuthate units in the solid state result in notable charge transfer and the appearance of unusual coloring. The nature of halogenhalogen interactions, which can be regarded as halogen bonding, in the obtained complexes was studied by QTAIM analysis, and their energies were estimated (1.3-3.6 kcal mol(-1)) and compared with those in related bromo- and iodoplumbates(ii). It is concluded that the presence of halogen bonding is not the single factor affecting the optical properties.