When considering f elements, solvent extraction is primarily used for the removalo fl anthanides from orea nd their recycling, as well as for the separationo fa ctinides from used nuclear fuel. Understanding the complexation mechanism of metal ions with organic extractants, particularly the influence of their molecular structure on complex formation is of fundamentali mportance.H erein, we report an extraordinary (up to two orders of magnitude)c hange in the extraction efficiency of f elements with two diastereomers of dimethyl tetraoctyld iglycolamide (Me 2 -TODGA), which only differ in the orientation of as inglem ethyl group. Solvente xtraction techniques, extended X-ray absorption fine structure (EXAFS)m easurements,a nd density functional theory( DFT) based ab initio calculations were used to understandt heir complex structures and to explain their complexation mechanism.W es how that the huge differences observed in extraction selectivity results from as mall changei nt he complexation of nitrate counter-ions caused by the different orientation of one methylg roup in the backboneo ft he extractant.T he obtained results give as ignificant new insight into metal-ligandc omplexation mechanisms,w hichw ill promote the development of more efficient separation techniques.Supporting information and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

The synthesis of [K(4.5) ⊂ (ClSn(II))8P8W48O184](17.5-), featuring Sn(II) ions in trigonal-pyramidal SnO2Cl environment coordinating to the two inner rims of the wheel-shaped {P8W48}-type polyoxotungstate(vi) archetype, showcases how high chloride ligand concentrations as well as the control of the polyanion solubility via electrolytes and evaporation rates are essential to prevent numerous competing reactions that can hamper the Sn(ii) functionalization of polyoxometalates.

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