Small-angle X-ray scattering to determine solution speciation of metal-oxo clusters

摘要

Molecular metal-oxo clusters are important intermediates between hydrated metal ions and metal oxides. They help elucidate the formation processes of metal oxides in nature and in synthesis; and they have numerous applications in catalysis, materials science, microbiology, separations and environmental science. Considerable focus is placed on determining the solid-state structures of these clusters. However, of equal and perhaps greater importance is the solution speciation of clusters. Small-angle X-ray scattering (SAXS) is a very powerful but underutilized technique to obtain speciation information of cluster solutions. This review highlights the type of information that can be obtained concerning the size and shape of clusters, interactions between clusters and evolution of cluster solutions with reactivity or aging. The X-ray studies discussed here include both simulated and experimental X-ray data of transition metal and actinide polyoxometalates, recently reported Hf-oxo polyanions and bismuth iron oxo clusters. Importantly and intentionally, all of the data presented herein was collected on a lab instrument, of which are becoming more commonly employed in all solution phase disciplines. This review is intended to inspire other researchers to determine how they could employ X-ray scattering in their own research in the wide range of disciplines that metal-oxo clusters impact. (C) 2016 Elsevier B.V. All rights reserved.