We have recently discovered1 that the 70-yr old industrial process for separating Hf4+ from Zr4+ depends on aqueous metal-oxo cluster chemistry. More broadly, we have reported2-3 that despite the identical behavior of Zr/Hf in geological and solid-state synthesis conditions, Zr/Hf are differentiated in aqueous metal-oxo cluster forming conditions. This has inspired us to explore the following fundamental questions more broadly: 1) In solutions of similar metals, do metal-cations self-sort into oxo-clusters via ‘narcissistic’ hydrolysis and condensation chemistry? and 2) Can we exploit these subtle differences in chemical behavior to invoke physical separations via solvent extraction or crystallization of self-sorted clusters? In this presentation, I will discuss divergent cluster types of Hf and Zr with different ligands (i.e. peroxide, thiocyanate), and what these studies have contributed to our fundamental knowledge of aqueous Hf and Zr chemistry. This includes new cluster topologies determined by crystallography, solution behavior analyzed by SAXS (small-angle X-ray scattering) and ESI-MS (electrospray ionization mass spectrometry), and both crystallization and solvent extraction processes as approaches to physical separation of self-sorted metal-oxo clusters. Both of these latter processes are controlled by the counterion, which is of primary importance in both self-assembly and many applications of metal-oxo clusters. In this F. Albert Cotton Award lecture, I will also talk briefly about our accidental discovery of Nb-polyoxometalates in 2002, leadingto my career foci and passions for discovering metal-oxo clusters from across the periodic table, ion-pairing in water and its role in fundamental processes in synthesis and nature.

Award Address (F. Albert Cotton Award in Synthetic Inorganic Chemistry sponsored by the F. Albert Cotton Endowment Fund). Are metal cations narcissistic in metal-oxo cluster formation?

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