Multiple Diastereomers of [Mn+(αm-P2W17O61)2](20-n)-(M=UIV, ThIV, CeIII;m=1, 2).Syn- andAnti-Conformations of the Polytungstate Ligands in α1 1, 1α2, and α2α2Complexes

Abstract

Several examples of the complexes, [M(P2W17O61)2] n− (M=UIV, ThIV, CeIII), containing both α 1 (C 1) and α 2 (C s ) isomers of the tungstophosphate ligands, have been synthesized and characterized by X-ray crystallography and 31P NMR spectroscopy. In every case the heteroatom M has the anticipated square antiprism coordination. When both ligands are α 2 (the UIV and CeIII complexes) the solid state structure adopts a syn-conformation of the ligands, as had been previously demonstrated for M=CeIV and LuIII; in solution a single set of P-NMR lines is observed, consistent with a single unique structure or rapid interconversion of syn- and anti-forms. When one or both ligands are α 1 (Uα 1 α 1, Uα 1 α 2, Thα 1 α 1, Ceα 1 α 2) multiline P-NMR spectra reveal the presence of two major diastereomers in solution, presumably the syn- and anti-forms. In the solid state, crystals of ammonium or potassium salts of the U and Ce complexes contain anti-conformers, while the Th complex proves to be syn. Variable temperature (∼25–∼60°C) P-NMR spectroscopy of solutions of the Uα 1 α 1 complex reveals the onset of syn-anti interconversion together with the irreversible formation of minor amounts of other diastereomers generated by dissociation and scrambling of the enantiomers of the polytungstate ligands.