Argentophilic interactions in multinuclear Ag complexes of imidazole containing Schiff bases

The reactions of imidazole groups containing Schiff bases, 1,2-bis[(1-methyl-2-imidazolyl)-methyleneamino] ethane (bmimen) and 1,3-bis[(1-methyl-2-imidazolyl)-methyleneamino]propane (bmimpn), with silver salts AgCF3SO3 and AgClO3 were studied. Five new silver complexes, [Ag-2(bmimen)(2)][CF3SO3](2)center dot CH3OH center dot CH3CN (1), [Ag-2(bmimen)(2)][CF3SO3](2)center dot 0.5H(2)O (2), [Ag-2(bmimen)(2)][ClO3](2)center dot CH3OH (3), [Ag-3(bmimen)(2)(mu-CF3SO3)(2)](2)[CF3SO3](4) (4) and [Ag(bmimpn)](n)[CF3SO3](n) (5), were synthesized and characterized. The Ag center dot center dot center dot Ag distances in compounds 1-5 depend on the length of the alkyl chain separating the imidazole ends of the ligand and the coordination mode of the bmimen and bmimpn. The shortest Ag center dot center dot center dot Ag distance of 2.7842(2) angstrom was found in 4. Such a short distance indicates a strong argentophilic interaction. Argentophilic interactions exist in each of the dinuclear structures 1-3 (Ag center dot center dot center dot Ag distances are 3.3348(5), 3.1873(3) and 3.0680(2) angstrom, respectively). The distance depends on crystal packing, which is determined by the counter ion and solvent molecules in the structure. In polymeric structure 5, the longer alkyl chain between the imidazole end units of the ligand pushes the metal centres further apart, the Ag center dot center dot center dot Ag separations being 3.6088(4) and 3.5279(4) angstrom. The results show that imidazole-based Schiff bases can be used to build multinuclear Ag compounds with variable silver-silver interactions.