Modular molecules: site-selective metal substitution, photoreduction, and chirality in polyoxometalate hybrids.

The first members of a promising new family of hybrid amino acid-polyoxometalates have emerged from a search for modular functional molecules. Incorporation of glycine (Gly) or norleucine (Nle) ligands into an yttrium-tungstoarsenate structural backbone, followed by crystallization with p-methylbenzylammonium (p-MeBzNH3(+)) cations, affords (p-MeBzNH3)6K2(GlyH)[As(III)4(Y(III)W(VI)3)W(VI)44Y(III)4O159(Gly)8(H2O)14]⋅47 H2O (1) and enantiomorphs (p-MeBzNH3)15(NleH)3[As(III)4(Mo(V)2Mo(VI)2)W(VI)44Y(III)4O160(Nle)9(H2O)11][As(III)4(Mo(VI)2W(VI)2)W(VI)44Y(III)4O160(Nle)9(H2O)11] (generically designated 2: L-Nle, 2 a; D-Nle, 2 b). An intensive structural, spectroscopic, electrochemical, magnetochemical and theoretical investigation has allowed the elucidation of site-selective metal substitution and photoreduction of the tetranuclear core of the hybrid polyanions. In the solid state, markedly different crystal packing is evident for the compounds, which indicates the role of noncovalent interactions involving the amino acid ligands. In solution, mass spectrometric and small-angle X-ray scattering studies confirm maintenance of the structure of the polyanions of 2, while circular dichroism demonstrates that the chirality is also maintained. The combination of all of these features in a single modular family emphasizes the potential of such hybrid polyoxometalates to provide nanoscale molecular materials with tunable properties.

Synthesis and characterization of novel simultaneous C and O-coordinated and nitrate-bridged complexes of silver(I) with carbonyl-stabilized sulfonium ylides and their antibacterial activities.

Reaction of sulfonium ylides (Me)(2)SCHC(O)C(6)H(4)R (R = H; m-NO(2); p-NO(2); p-OMe; p-Me and p-Br) with AgNO(3) in dichloromethane leads to various compounds. Single crystal X-ray diffraction analysis reveals that the adducts take 3 forms: (i) two-dimensional polymer, [AgNO(3)(Me(2)SCHC(O)C(6)H(5))](n) (1), with nitrate bridges in which each nitrate coordinates to three silver atoms through two oxygen atoms and two Me(2)SCHC(O)C(6)H(5) ligands coordinate to silver centers through carbon atoms; (ii) cationic binuclear, [Ag(Me(2)SCHC(O)C(6)H(4)-m-NO(2))(2)](2)(NO(3))(2)·2H(2)O (2), in which Me(2)SCHC(O)C(6)H(4)-m-NO(2) ligands simultaneously coordinate through both carbon and oxygen atoms with nitrate as a counter ion, and (iii) cationic mononuclear and anionic binuclear, [Ag(Me(2)SCHC(O)C(6)H(4)-p-NO(2))(2)](2)[{AgNO(3)(µ-NO(3)) (Me(2)SCHC(O)C(6)H(4)-p-NO(2))}(2)]·2CH(3)OH (3), in which nitrate groups act as bridging as well as terminal ligands, and Me(2)SCHC(O)C(6)H(4)-p-NO(2) ligands display C-coordination. Characterization of the obtained compounds was also performed by infrared, (1)H- and (13)C-NMR spectroscopy and analytical data indicated a 1 : 2 stoichiometry between the silver(I) nitrate and ylide p-OMe (4) and 1 : 1 for ylides p-Me (5) and p-Br (6). In addition, the antibacterial effects of DMSO-solutions of complexes 1-6 were evaluated by the agar disc diffusion method against three Gram positive and three Gram negative bacteria. All complexes displayed antibacterial activity against these bacteria, with high levels of inhibitory potency exhibited against the Gram negative species.