Viologen-templated bromoplumbate: a new in situ synthetic method and energy gap engineering†
Changing N-substituents to modify energy gaps is important for the diverse applications (photochromism, photocatalysis, etc.) of viologen-based compounds. In situ N-substitution using alcohols under solvothermal and acidic conditions is an effective and common synthetic method for viologen-templated metal halides. In this work, we found that replacing alcohols with alkenes could reduce the reaction temperature dramatically to room temperature. A new cis/trans-viologen-templated bromoplumbate with a novel 1-D chain structure built by edge-sharing planar [Pb3Br9]3− oligomers was successfully obtained. This bromoplumbate hybrid has a narrower energy gap compared with bulk PbBr2, which has been well explained by linear optical response spectra calculations and PDOS analysis.