Multiple diastereomers of [Mn+(αm-P2W17O61)2](20-n)- (M=UIV, ThIV, CeIII; m=1, 2).: Syn- and anti-conformations of the polytungstate ligands in α1α1, α1α2, and α2α2 complexes

Several examples of the complexes, [M(P2W17O61)(2)](n-) (M = U-IV, Th-IV, Ce-III), containing both alpha(1) (C-1) and alpha(2) (C-s) isomers of the tungstophosphate ligands, have been synthesized and characterized by X-ray crystallography and P-31 NMR spectroscopy. In every case the heteroatom M has the anticipated square antiprism coordination. When both ligands are alpha(2) (the U-IV and Ce-III complexes) the solid state structure adopts a syn-conformation of the ligands, as had been previously demonstrated for M=Ce-IV and Lu-III; 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 alpha(1) (Ualpha(1)alpha(1), Ualpha(1)alpha(2), Thalpha(1)alpha(1), Cealpha(1)alpha(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 (similar to 25 - similar to 60 degreesC) P-NMR spectroscopy of solutions of the Ualpha(1)alpha(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.