CuII Complexes with (2-benzylidenehydrazinyl)- 4- Phenylthiazole Ligands: An Experimental and Theoretical Study

CuII complexes of (E)-2-(2-benzylidenehydrazinyl)-4-phenylthiazole, L1, (E)-2-(2-(4 chlorobenzylidene)hydrazinyl)-4-phenylthiazole, L2, and(E)-2-(2-(4- methoxybenzylidene)hydrazinyl)- 4-phenylthiazole L3 ligands were prepared and characterized by spectroscopic methods. The EPR spectroscopy indicates the formation of two complexation products for L2 and L3, but of one major product for L1. The spectrum of CuL1 shows hyperfine parameters A║ = 122(±1) G and g|| = 2.40(±0.01); A┴ = 13(±2) G and g┴ = 2.08(±0.02). The spectra of both CuL2 and CuL3 show two different species, the most prominent one with the same hyperfine parameters measured for CuL1, and the second one with hyperfine parameters A║ = 109(±2) G and g|| = 2.36(±0.02); A┴ = 10(±2) G and g┴ = 2.06(±0.02). The EPR spectra of both species are typical of tetragonal-distorted environments around the CuII center. Semi-empirical calculations at the PM6 level of the ligands indicate the possibility of different conformers under the reactional conditions, suggesting that the different species measured in the EPR spectra should be cis/trans isomers. Semi-empirical calculations at the PM3 level of the complexes suggest that the reaction products should actually be a mixture of (preferentially) trans and cis N1-S structures. These results are corroborated by the FARIR and EPR spectra.