Crystal structures of low-melting ionic transition-metal complexes with N-alkylimidazole ligands
This experiment synthesized and characterized ionic liquids with Cu(II), Ni(II) or Co(II) with single crystal X-ray diffraction. The synthesized compounds consist of N-methylimidazole (MeIm), N-ethylimidizole (EtIm), N-butylimidazole (BuIm), and N-hexylimidazole ligands coordinated around the metal centers of copper, nickel, or cobalt. The charge of the compounds are balanced by the bis(trifluoromethyl)sulfyonyl imide (Tf2N). The compounds formed in either square planar geometry or octahedral, which had the same general formula of [Cu(AlkIm)4][Tf2N]2 (AlkIm=MeIm, EtIm, BuIm, and HeIm) or [M(MeIm)6][Tf2N]2 (M=Cu, Ni, Co). The general synthesis of each compound was to first make the ligand. The metal Tf2N salt was dissolved in ethanol and the appropriate amount of ligand was added and the solution was stirred for 5 minutes. In order to evaporate out the ethanol and leave a solid/liquid, the solution was condensed on a rotary evaporator. The solid products were washed with diethyl ether and all the products (liquid or solid) were dried for 4 days at 50°C. The melting points were found to be dependent on alkyl chain length and choice of metal ion, ranging from below room temperature to slightly above room temperature. For complexes with octahedral geometry, the melting point varies significantly when using Cu(II) rather than Co(II) or Ni(II). X-ray diffraction was used to determine the structure of the compounds that were suitable.