Functionalization of Polyoxometalates by a Negatively Charged Bridging Ligand: The Dimeric [(SiW11O39Ln)2(μ‐CH3COO)2]12− (Ln = GdIII, YbIII) Complexes

The possibility of coupling lacunary polyoxometalates through a cationic center present in the vacancy by negatively charged organic ligands is demonstrated for the first time by single‐crystal X‐ray diffraction. The structure of the dimeric K12[{Yb(α‐SiW11O39)(H2O)}2(μ‐CH3COO)2]·38H2O complex, where two acetato ligands connect the ytterbium centers in a (η2, μ‐1,1) fashion, is reported. Using gadolinium instead of ytterbium, both the isostructural dimeric compound K12[{Gd(α‐SiW11O39)(H2O)}2(μ‐CH3COO)2]·38H2O and the mononuclear sandwich complex [Gd(SiW11O39)2]13− can be selectively isolated, depending on the synthetic conditions. The magnetic properties of the dimeric gadolinium complex are presented. The influence of the nature of the rare‐earth metal on the final compound is further highlighted by the fact that when praseodymium is used as the rare‐earth element, only the sandwich compound can be obtained. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)