Argentophilic interactions in multinuclear Ag complexes of imidazole containing Schiff bases

Abstract

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, [Ag₂(bmimen)₂][CF₃SO₃]₂·CH₃OH·CH₃CN (1), [Ag₂(bmimen)₂][CF₃SO₃]₂ ·0.5H₂O (2), [Ag₂(bmimen)₂][ClO₃]₂·CH₃OH (3), [Ag₃(bmimen)₂(μ-CF₃SO₃)₂]₂[CF₃SO₃]₄ (4) and [Ag(bmimpn)]_n[CF₃SO₃]_n (5), were synthesized and characterized. The Ag⋯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⋯Ag distance of 2.7842(2) Å 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⋯Ag distances are 3.3348(5), 3.1873(3) and 3.0680(2) Å, 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⋯Ag separations being 3.6088(4) and 3.5279(4) Å. The results show that imidazole-based Schiff bases can be used to build multinuclear Ag compounds with variable silver–silver interactions.