The coordination chemistry of trivalent lanthanides (Ce, Nd, Sm, Eu, Gd, Dy, Yb) with diphenyldithiophosphinate anions

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Understanding the coordination chemistry between lanthanide elements and dithiophosphinate ligands is important given prospects for using dithiophosphinate ligands to separate trivalent minor actinides from lanthanides in advanced nuclear fuel cycles. Reported here is the coordination chemistry of a series of lanthanide elements (Ce, Nd, Sm, Eu, Gd, Dy, and Yb) with diphenyldithiophosphinate anions, S2PPh21−. In all cases, LnCl3 was reacted with 4 equivalents of S2PPh21−. The large lanthanides (Ce3+, Nd3+, Sm3+, Eu3+) formed eight coordinate anions of the general formula Ln(S2PPh2)41− and were characterized by 1H and 31P NMR, IR, UV–Vis, elemental analysis, and single crystal X-ray crystallography. For the slightly smaller Gd3+ and Dy3+ ions, a break in reactivity was observed. Here, analyses of reaction solutions by 1H and 31P NMR spectroscopy suggested that a complicated mixture formed from which single crystals of eight coordinate and neutral Gd(S2PPh2)3(NCMe)2 and Dy(S2PPh2)3(NCMe)2 complexes were isolated. Reactions involving even smaller Yb3+ ions provided similar results to Gd3+ and Dy3+, in that reaction solutions also contained a mixture of products. In the Yb3+ case a new heteroleptic species [Ph4P][Yb(S2PPh2)3Cl], was isolated in single crystal form. The structural data have been presented in comparison to that of [Ph4P][Sm(S2PMe2)4] and [Ph4P][Eu(S2PMe2)4], which were also structurally characterized for the first time. Overall, these results demonstrate how subtle differences in lanthanide ionic radii can drastically affect the coordination number, ligand stoichiometry, and charge on the resulting diphenyldithiophosphinate complex.