The oxido clusters of bismuth
The oxido clusters of bismuth have received increasing attention over the past several decades. This can in part be attributed to the use of bismuth compounds as pharmaceuticals, dating back hundreds of years for treating gastrointestinal disorders and as general antimicrobial and antifungal agents. This is enabled by bismuth's low toxicity compared to its more infamous neighbors in the periodic table. The field received a substantial boost in activity aimed at producing precursor compounds to homo- and heterometallic metal oxides via sol gel syntheses thanks to the discovery of various high TC superconducting bismuth-containing phases. More recently these compounds have shown interesting catalytic, electronic and optical properties. There is a strong resemblance of the structures of the oxido species to solid state bismuth oxides, and the chemistry of the oxido clusters is strongly intertwined with the fundamental coordination chemistry of bismuth, which shows strong Lewis acidity and high coordination numbers. As a result, the oxido clusters of bismuth have proven to have a rich structural chemistry with nuclearities ranging from two to fifty bismuth atoms, and many structures are known that incorporate other metals including the alkali metals, alkaline earth metals, transition metals and lanthanides as part of the oxido core. Compounds with a [Bi6O4(OH)4]6+ core are particularly prevalent, but Bi4, Bi9 and Bi38 structures are also well-represented. The ligand sets that support the formation and stabilization of these structures include a wide variety of organic alkoxides, siloxides, carboxylates, sulfonates, phosphonates and acetylacetonates. Multifunctional ligands have been used for the production of MOF-like structures via hydrothermal methods that can result in discrete bismuth oxido clusters linked via ligand bridges or polymeric bismuth oxido structures decorated with the organic ligands and organized into 1-, 2- or 3-dimensional structures. This review is designed to summarize the synthetic methods used to prepare them, present key aspects of their physical and chemical properties as well as discussing the important features of the structures reported to date. Of significant importance is the obvous blurring of the boundaries between the discrete bismuth oxido clusters that can be described as conventional inorganic coordination compounds, organobismuth oxides and oxido bismuth compounds where the bismuth oxido core is itself a polymer.
Whitmire, Kenton H. and Wall, Kathryn. "The oxido clusters of bismuth." Coordination Chemistry Reviews, 488, (2023) Elsevier: https://doi.org/10.1016/j.ccr.2023.215072.