The geometry of the silver 1,10-dibenzyl-2,20-biimidazole complexes

摘要

The argentophilic interactions and interactions of weakly coordinated nitrate and water with silver metal were studied by investigating the reaction of 1,1'-dibenzyl-2,2'-biimidazole (Bn_2bim) with silver nitrate. Three new silver complexes [Ag_4(Bn_2bim)_4(NO_3)_2]·4(CH_3CH_2OH)·2(NO_3)·0.5(H_2O) (1), [Ag_4(Bn_2bim)_4 (H_2O)_4]·4(NO_3) (2) and [Ag_4(Bn_2bim)_4(NO_3)_4]·6(CH_2Cl_2)·2(H_2O) (3) were synthesized and characterized. Complexes 1-3 have rare tetranuclear twisted closed cyclic structure with four bridging biimidazoles and variable nitrate/water ratio. The interactions between the nitrate ligand and Ag as well as water ligands and Ag are considered to be weak due to the ease of exchanging them. The structure 1 consists of a discrete tetranuclear complex with two short Ag- - -Ag distances of 3.0984(10) ? and 3.1994(10) ?, which indicates argentophilic interactions. The complex 2 forms linear assemblies of tetranuclear moieties via hydrogen bonding through weakly coordinated aqua ligand and NO_3~-counteranions. Crystallization from a mixture of dichloromethane and n-hexane led to an exchange of H_2O ligands to nitrates and formation of a new discrete tetranuclear complex 3. Unlike 1, the more open structures of 2 and 3 did not show any argentophilic interactions. The two shortest Ag- - -Ag distances for complexes 2 and 3 were 4.6508(8) ? and 4.9517(5) ? and 4.5810(5) ?-5.0050(5) ? respectively. The overall energetics and the effect of the H2O molecules and the nitrate anions on the geometries of the Ag complexes were studied by computational DFT methods.