Synthesis, structure, and properties of bis(2-(1-ethyl-1H-imidazol-4-yl)acetate) copper(II)

Ethylation of imidazole-4-acetate methyl ester affords 1-ethyl-1H-Imidazol-4-ylacetic acid methyl ester (1) and 1-ethyl-1H-Imidazol-5-ylacetic acid methyl ester (2) in a 3:1 ratio. Both 1 and 2 can be converted to their potassium carboxylate salts, 3 and 4, respectively. Reaction of 3 with CuCl2 in methanol yields [Cu(eia)2]·4MeOH (5·4MeOH) (eia− = 1-ethyl-1H-imidazol-4-yl)acetate). EPR measurement of 5 in methanol glass exhibits near axial symmetry with g⊥ (gx = 2.060, gy = 2.087) and g|| = gz = 2.293 with A||Cu = AzCu = 152 G, A⊥Cu~ 10 G, and AyN = 14 G. Accordingly, the structure of 5·4MeOH reveals Cu(II) in tetragonally distorted octahedral geometry with O, N coordination from eia− and elongated bonding (2.506 Å) to methanol oxygens in the axial positions. An infinite 1-dimensional hydrogen bonding network involving methanol molecules is present. DFT studies have been carried out to assist in assignment of electronic transitions. Electrochemical studies on 5 in methanol and DMF reveal quasi-reversible redox behavior for the CuII/I couple while for MeCN a CuI/0 stripping process is seen.