ELECTRONIC STRUCTURES OF MIXED METAL SUB-OXIDE CLUSTERS

Metal oxide clusters possess electronic, chemical, and physical properties that reflect the complex properties of defective bulk metal oxide materials, the importance of which is difficult to overstate when considering their ubiquity in applications ranging from catalysis to spintronics. Choice of binary metal combinations adds an important dimension in efforts to enhance and tune the properties of oxides, which are further affected by manipulating the oxidation state. We have explored the intrinsically local phenomena arising from mixed metal oxides, particularly in lower-than-traditional oxidation states (sub-oxides), by applying anion photoelectron spectroscopy and density functional theory calculations to the study of small mixed metal sub-oxide clusters. Anion photoelectron spectroscopy is a mass-selective method that probes the energies of the manifold of low-lying electronic states inherent in neutral sub-oxide species. By coupling experimental with computational results, a detailed picture of how mixed metal composition impacts molecular and electronic structure emerges. For example, profoundly asymmetric metal-oxygen bond formation in near-neighbor mixed transition or lanthanide metal oxides can be reconciled with relative oxophilicities, and the prevalence of antiferromagnetic spin states can be reconciled with localization of metal atomic orbitals in mixed systems. Striking charge separation is observed in trans-periodic mixed metal oxides that combine transition and post-transition metals, or transition and lanthanide metals, combinations that are evocative of strongly-interacting catalyst-support systems. Finally, we consider whether more can be gleaned from anion photoelectron spectroscopy of these exceptionally complex systems by exploiting the electron-kinetic-energy-dependent neutral-electron interactions