Résumé
Three {Ru(p-cym)}2+ (p-cym = p-cymene) derivs. of [Nb6O19]8--[Nb6O19{Ru(p-cym)}]6- (Nb6Ru1), trans-[Nb6O19{Ru(p-cym)}2]4- (t-Nb6Ru2), and [Nb6O19{Ru(p-cym)}4] (Nb6Ru4)-have been synthesized in water by reaction between [Ru(p-cym)Cl2]2 and the hexaniobate. In the solid state, Nb6Ru1 and Nb6Ru4 have been characterized by IR and EDX spectroscopies, whereas t-Nb6Ru2 has been characterized by IR spectroscopy and single-crystal x-ray diffraction (crystal data for K4-trans-[Nb6O19{Ru(p-cym)}2].14H2O (K4-t-Nb6Ru2.14H2O)). In soln., all compds. were characterized by 1H NMR and ESI mass spectrometry analyses, and Nb6Ru1 was also analyzed by 17O NMR. These studies allowed a comparison of the differences in behavior of the three complexes in water: Nb6Ru1 is particularly stable, Nb6Ru4 decomps. by loss of {Ru(p-cym)}2+ fragments, and trans-[Nb6O19{Ru(p-cym)}2]4- isomerizes into cis-[Nb6O19{Ru(p-cym)}2]4-. A rational mechanism for the isomerization of t-Nb6Ru2 is proposed on the basis of a kinetic study.