Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The coordination chemistry of actinides (An) using model ligands helps to deeply understand their bonding situation on a molecular level. However, the basic An chemistry is still little explored. Characteristic of An is a huge variety of possible oxidation states, typically ranging from II to VII for early An. A suitable approach to explore the fundamental phico-chemical properties of An is to study a series of isostructural An compounds in the same oxidation state. Observed changes in e.g. the binding situation or magnetic effects among the An series could deliver insight into their unique electronic properties mainly origination from the f-electrons. A question still remaining in An chemistry is the degree of "covalency". However, studies covering TRU elements are rather scarce. Against this background, we are strongly motivated to perform a systematic comparison of isostructural An complexes (Th, U and Np).
In this study we investigate the coordination chemistry of tetravalent actinides (An(IV)) for two major reasons: a) the series of An(IV) is the largest accessible one within the early actinides, and b) the tetravalent state is the dominant one particularly under anoxic conditions. The ligands used in this study range from hard- (oxygen) and medium- (nitrogen) to pure soft-donor (carbon) character, according to Pearsons's HSAB concept. Due to the expected changes in orbital overlap between the metal and ligand, the formed complexes could further provide us a deep insight into the electronic situation of the actinides.
The An(IV) complexes are characterised in solution by NMR-, IR- and UV-vis spectroscopy as well as in the solid-state by SC_XRD. The acquired experimental results are further supported by quantum chemical calculations with a focus on the electronic structure of the complexes.