In Search of Covalency in Tetravalent Actinide (Th - Pu) Monosalen Complex Series


In Search of Covalency in Tetravalent Actinide (Th - Pu) Monosalen Complex Series

Blei, M. K.; Patzschke, M.; Kvashnina, K.; Waurick, L.; Schmidt, M.; Stumpf, T.; März, J.

Actinides play an important role in chemical engineering and environmental science related to the nuclear industry or nuclear waste repositories.[1] One of the major tools to obtain a profound basic knowledge about actinide (An) binding is the coordination chemistry of An using model ligands. However, fundamental An chemistry is still relatively little explored. Characteristic of the actinides is their huge variety of possible oxidation states, typically ranging from +II to +VII for early An, making their chemistry complex but interesting. A suitable approach to explore fundamental physico-chemical properties of the actinides is to study series of isostructural An compounds in which the An is in the same oxidation state.[2] Observed changes in e.g. the binding situation or magnetic effects among the An series may deliver insight into their unique electronic properties mainly originating from the f-electrons. A question still remaining in the field of An chemistry is the degree of “covalency” in compounds across the An series,[3] which may be addressed by systematic studies on series of An compounds, including transuranium (TRU) elements.
In this study we investigate the coordination chemistry of tetravalent actinides (An(IV)), which are dominant particularly under anoxic environmental conditions, using the organic salen ligand (salen = N,N’-bis(salicylidene)ethylenediamine) as a small N,O donor.[4] In addition, we change halogen (F, Cl, Br, I) and solvent (MeOH, THF, MeCN, pyridine) donors (see Figure 1) in order to analyse the ligand’s effect on covalency trends as well as their mutual influence, mainly using single crystal X-ray diffraction (SC-XRD), high-energy-resolution fluorescence detection X-ray absorption near edge spectroscopy (HERFD-XANES), and quantum chemical calculations (QCC).

Keywords: actinides; complexes; SC-XRD; quantum chemical calculations; thorium; uranium; neptunium; plutonium; N-donor ligands

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Publ.-Id: 35642