Tripodal bis(imidazole)-based ligands and their chelation to copper(ii)

Abstract

Three new copper(II) compounds are described containing chelating bis(imidazole)-based ligands. Compound 1, [Cu₂(L1)₂(H₂O)₂][SiF₆]₂·10H₂O, was obtained by reaction of [bis-(1H-imidazol-2-yl)-methyl]-pyridin-2-ylmethyl-amine (L1) with Cu(BF₄)₂·6H₂O in a glass vessel for a few weeks. The single-crystal X-ray structure of 1 consists of dinuclear copper(II) units, formed through ligand sharing. The starting BF₄⁻ anion was replaced by the SiF₆²⁻ in the crystal structure of 1. In the crystal lattice, a discrete (H₂O)₈ cluster forms an eight-membered ring and is linked through four shared water molecules with the other (H₂O)₈ cluster. Both water clusters show hydrogen-bonding interactions with the neighbouring SiF₆²⁻ anion. To investigate the effect of the presence of a bridging ligand such as oxalate on the coordination chemistry of L1 and copper(II) ion, compound 2, [Cu₂(L1)(H₂O)₂][Cu(C₂O₄)₂(ClO₄)₂]·2H₂O, was prepared by reaction of L1 and Cu(ClO₄)₂·6H₂O in the presence of oxalic acid; the crystal structure is built from 4+ and 4− ions in the crystal lattice. Compound 3, [Cu(ClO₄)(C₂O₄)(HL2)H₂O]·2H₂O, was formed from the reaction of ligand [bis-(1H-imidazol-2-yl)-methyl]-isopropyl-amine (L2) and Cu(ClO₄)₂·6H₂O in the presence of oxalic acid. The isopropylamine group is not coordinated to the copper in this case, but protonated. In compound 3, a mononuclear copper(II) unit is present, built from a bidentate L2, a bidentate oxalate, a monodentate perchlorate and a water. Two copper coordination entities are doubly bridged through hydrogen bonds with twice the pathway [Cu–O_C2O4–(O_water)–Cu] to form a dimeric-like species. Low-temperature magnetic susceptibility studies showed no interaction between copper(II) ions.