Dicarboxylatodirhodium derivatives of polyoxotungstates

Salts of the new complexes [PW11O39{Rh2(O2CR)2}]5−; R = Prn (1), CH2Cl (2), CH2OH (3), o-C6H4OH (4), p-C6H4OH (5), and [XW11O39{Rh2(p-O2CC6H4OH)2}]6−; X = Si (6), Ge (7) have been prepared in good yield and characterized by elemental analysis, multinuclear NMR spectroscopy, and structural crystallography of the cesium salts of anions 1 and 5 with chloride ions in axial positions of the dirhodium moiety. The incorporation of the dirhodium group into the Keggin structure significantly increases the hydrolytic kinetic stability of the polyoxotungstates at pH 7–8.5, a result that has implications for the use of such complexes for imaging and for phase determination in structural studies of large biomolecules. Based on NMR studies, the axial sites of the dirhodium moiety of the polytungstate anions are accessible to ligation by molecules such as cysteine, methionine, and isonicotinic acid.