Ionic liquids from copper(II) complexes with alkylimidazole-containing tripodal ligands.

Five-coordinate copper(II) complexes [Cu(L)Cl]X bearing alkylimidazole-containing tripodal ligands were prepared, where L = bis(2-dimethylaminoethyl)-((1-alkylimidazol-2-yl)methyl)amine and X = bis(trifluoromethanesulfonyl)amide (Tf2N) and PF6. The salts with hexyl ([1]X), propyl ([2]X), and methyl ([3]X) substituents in the ligand were prepared, of which [1]Tf2N and [2]Tf2N were ionic liquids with high viscosity at room temperature. X-ray crystal structure determination at low temperature revealed that the coordination geometry around the metal ion in [3]Tf2N was distorted trigonal bipyramidal, whereas that in [2]PF6 was close to square pyramidal. UV-vis absorption spectra of these salts were consistent with the coordination structures.