Experimental and theoretical study of the regiospecific coordination of RuII and OsII fragments on the lacunary polyoxometalate [alpha-PW11O39]7-.

New Ru(II) and Os(II) derivatives of the monovacant alpha-PW(11)O(39) anion (PW(11)O(39){M(DMSO)(3)(H(2)O)} (M = Ru (1), Os (2)) and PW(11)O(39){Os(eta(6)-p-cym)(H(2)O)} (3)) have been synthesized and characterized. The binding mode of the d(6)-{M(II)L(3)(H(2)O)}(2+) moieties in these compounds is similar to that in the previously described PW(11)O(39){Ru(eta(6)-p-cym)(H(2)O)} (4) complex: bidentate, on two nonequivalent oxygen atoms of the lacuna, leading to a loss of the C(s) symmetry of the parent anion, which thus plays the role of a prochiral bidentate ligand. The density functional theory (DFT) (B3PW91) computation of the lowest unoccupied molecular orbitals of the {ML(3)(H(2)O)}(2+) (M = Os, Ru; L(3) = fac-(DMSO)(3), eta(6)-C(6)H(6)) fragments reveals the similarities between their electrophilic properties. The origin of the regioselectivity of the grafting was investigated through a DFT (B3PW91) analysis of (i) the highest occupied molecular orbital of alpha-PW(11)O(39) and (ii) the relative energies of the different potential regioisomers obtained by a bidentate grafting of the {ML(3)(H(2)O)}(2+) moiety onto the lacuna of alpha-PW(11)O(39). The role of the water ligand in the stabilization of this peculiar structure was studied.