Synthesis and first-principles study of structural, electronic and optical properties of tetragonal hybrid halobismuthathes [Py2(XK)]2[Bi2Br10−xIx]

The preparation of new hybrid halobismuthates [Py2(XK)]2[Bi2Br10], [Py2(XK)]2[Bi2I10], and the [Py2(XK)](I3)2 polyiodide ([Py2(XK)]2+ = 1,1′-(1,4-phenylenebis(methylene))bis(1-pyridinium)) is reported. The significant deviation of unit cell parameters from Vegard's law in a series of solid solutions [Py2(XK)]2[Bi2Br10−xIx] is shown. The specifics of halogen atom substitution was discussed based on the site occupancy study derived from powder X-ray diffraction data. The bridging atom positions were determined to be more attractive for iodine atoms than the terminal positions in the anionic framework. According to the electronic density of states (DOS) calculations, it is the bridging halogen atoms that are involved in the charge transfer and determine the optical properties of the compound.