cis-Bis(bipyridine)ruthenium Imidazole Derivatives:  A Spectroscopic, Kinetic, and Structural Study

The ruthenium bis(bipyridine) complexes cis-[Ru(bpy)₂Im(OH₂)]²⁺, cis-[Ru(bpy)₂(Im)₂]²⁺, cis-[Ru(bpy)₂(N-Im)₂]²⁺, cis-[Ru(dmbpy)₂Im(OH₂)]²⁺, cis-[Ru(dmbpy)₂(N-Im)(OH₂)]²⁺(bpy = 2,2‘-bipyridine, dmbpy = 4,4‘-dimethyl-2,2‘-bipyridine, Im = imidazole, N-Im = N-methylimidazole), have been synthesized under ambient conditions in aqueous solution (pH 7). Their electrochemical and spectroscopic properties, absorption, emission, and lifetimes were determined and compared. The substitution kinetics of the cis-[Ru(bpy)₂Im(OH₂)]²⁺ complexes show slower rates and have lower affinities for imidazole ligands than the corresponding cis-[Ru(NH₃)₄Im(OH₂)]²⁺ complexes. The crystal structures of the monoclinic cis-[Ru(bpy)₂(Im)₂](BF₄)₂, space group = P2₁/a, Z = 4, a = 11.344(1) Å, b = 17.499(3) Å, c = 15.114(3) Å, and β = 100.17(1)°, and triclinic cis-[Ru(bpy)₂(N-Im)(H₂O)](CF₃COO)₂·H₂O, space group = P1̄, Z = 2, a = 10.432(4) Å, b = 11.995(3) Å, c = 13.912(5) Å, α = 87.03(3)°, β = 70.28(3)°, and γ = 71.57(2)°, complexes show that these molecules crystallize as complexes of octahedral Ru(II) to two bidentate bipyridine ligands with two imidazole ligands or a water and an N-methylimidazole ligand cis to each other. The importance of these molecules is associated with their frequent use in the modification of proteins at histidine residues and in comparisons of the modified protein derivatives with these small molecule analogs.