Metal alkoxides as models for metal oxides—the concept revisited

Sol-Gel synthesis of metal oxides constitutes a tremendously exciting domain of inorganic chemistry, where molecular and supramolecular science meet the physical chemistry and materials science. Structure and reactivity, especially surface complexation of biologically important molecules on the surface of metal oxide nanoparticles can efficiently be traced through structural studies of metal oxo-paperbags—the product of partial hydrolysis of alkoxide precursors. Paperbag is a recently proposed term to denote oligonuclear complexes not featuring intrinsic metal-metal bonding and thus not qualified to be called “clusters”. Another important insight, provided recently by the studies of heterometallic species, is dealing with visualization of bonding modes of single atom catalysts on metal oxide substrates and reveals possible coordination environments of heteroatoms on doping. The studies of large paperbag aggregates can contribute to understanding of factors influencing the bandgap and photocatalytic activity of related oxides. The use of these species directly as photo or electro catalysts is rather debatable, however, in the view of high reactivity of these alkoxide intermediates, easily transforming them into metal oxide nanoparticles on hydrolysis or thermolysis.