Dept. of Chemistry Seminar – Professor Scott R. Daly

About the event

Speaker: Prof. Scott R. Daly, Associate Professor of Chemistry, University of Iowa

Host: James Boncella

Title: Assessing Metal-Ligand Covalency in Actinide and Transition Metal Complexes Containing Hydride and Phosphorus Ligands

Abstract: Covalent metal-ligand bonding governs the electronic properties, molecular structures, and reactivity of many metal complexes, and it has long been suspected as a key contributor in the selectivity of effective actinide extractants used in f-element separations. A prominent experimental challenge is quantifying the extent of metal-ligand covalency in metal complexes so that it can be used to identify and enhance desirable ligand design parameters for metal-specific applications. Metal-ligand bond distances are often used to assess variations in covalency across structurally similar complexes, but there have been questions about the reliability of this approach, especially with f-elements.

In this talk, I will describe the synthesis of trivalent f-metal complexes with chelating, phosphorus-bridged borohydrides called phosphinodiboranates. I will show how these complexes exhibit structural differences that allowed us to quantify the influence of metal-ligand covalency on differing lanthanide and actinide reactivity in solution. I will then describe how we used a technique called ligand K-edge X-ray absorption spectroscopy to assess the reliability of using metal-ligand bond distances to determine covalency variations in transition metal complexes. The implications of these results will be discussed with respect to applications in homogeneous catalysis and the suspected role of covalency in effective trivalent f-element separations.