Chemistry of azoimidazoles: Synthesis, spectral characterization and redox properties of bis(N(1)-alkyl-2-(arylazo)imidazole) copper(I) and silver(I) complexes

Article abstract of DOI:10.1016/S0277-5387(97)00127-7

N(1)-Alkyl-2(arylazo)imidazoles p-C₆H₄N=NC₃H₂N N(1)R′, RaaiR′, R′ = Me (2), Et (3); R = H(a), Me(b), OMe(c), Cl(d), NO₂(e) yield catonic bis-chelated complexes with both copper(I) (4,5) and silver(I) (6,7). These were isolated as perchlorate salts and the composition is supported by elemental analyses. The complexes are 1:1 electrolytes in methanol. The N=N stretch in copper(I) complexes shows a large shift to lower frequency (ca 1335 cm^-1) from the free ligand value (ca 1400 cm^-1) due to d(Cu) → π* (RaaiR′) back bonding. This effect is much less pronounced in silver(I) complexes indicating a negligible dπ-π* (RaaiR′) interaction. The complexes show highly resolved symmetrical ¹H NMR spectra. The copper(I) complexes exhibit intense MLCT transitions in the visible region. In methanol the Cu(RaaiR′)²⁺₂/Cu(RaaiRprime;)⁺ ₂ couple has E_1/2 ca 0.45 V vs SCE at 298 K. The high positive potential may be due to the distortion in the geometry of Cu(RaaiR)⁺₂.