Syntheses and characterization of dinuclear and tetranuclear Ag supramolecular complexes generated from symmetric and asymmetric molecular clips containing oxadiazole rings.

A new asymmetric ligand, 5-{3-[5-(4-methylphenyl)-1,3,4-oxadiazol-2-yl]phenyl}-2-(pyridin-3-yl)-1,3,4-oxadiazole (L5), which contains two oxadiazole rings, was synthesized and characterized. The assembly of symmetric 2,5-bis(pyridin-3-yl)-1,3,4-oxadiazole (L1) and asymmetric L5 with AgCOCF in solution yielded two novel Ag complexes, namely catena-poly[[di-μ-trifluoroacetato-disilver(I)]-bis[μ-2,5-bis(pyridin-3-yl)-1,3,4-oxadiazole]], [Ag(CFO)(CHNO)] or [Ag(μ-OCCF)(L1)] (1), and bis(μ-5-{3-[5-(4-methylphenyl)-1,3,4-oxadiazol-2-yl]phenyl}-2-(pyridin-3-yl)-1,3,4-oxadiazole)tetra-μ-trifluoroacetato-tetrasilver(I) dichloromethane monosolvate, [Ag(CFO)(CHNO)]·CHCl or [Ag(μ-OCCF)(L5)]·CHCl (2). Complex 1 displays a one-dimensional ring-chain motif, where dinuclear Ag(CFCO) units alternate with Ag(L1) macrocycles. This structure is different from previously reported Ag-L1 complexes with different anions. Complex 2 features a tetranuclear supramolecular macrocycle, in which each ligand adopts a tridentate coordination mode with the oxadiazole ring next to the p-tolyl ring coordinated and that next to the pyridyl ring free. Two L5 ligands are bound to two Ag1 centres through two oxadiazole N and two pyridyl N atoms to form a macrocycle. The other two oxadiazole N atoms coordinate to the two Ag2 centres of the Ag(OCCF) dimer. Each CFCO anion adopts a μ-coordination mode, bridging the Ag1 and Ag2 centres to form a tetranuclear silver(I) complex. This study indicates that the donor ability of the bridging oxadiazole rings can be tuned by electron-withdrawing and -donating substituents. The emission properties of ligands L1 and L5 and complexes 1 and 2 were also investigated in the solid state.