First example of ruthenium-azoimine-chloranilates: synthesis, structure, spectra and electrochemistry of ruthenium(II) 1-alkyl-2-(arylazo)imidazole chloranilates, and correlation of electronic properties with ZINDO calculation

Ag⁺-assisted dechlorination of blue cis-trans-cis Ru(R-aai-R^′)₂Cl₂ followed by the reaction with chloranilic acid (H₂CA) in presence of Et₃N gives a neutral mononuclear violet complex Ru(R-aai-R^′)₂(CA)]. R-aai-R^′=p-R-C₆H₄-NN-C₃H₂-NN-1-R^′, abbreviated as N,N^′ chelator, where N(imidazole) and N(azo) represent N and N^′, respectively; R=H (a), Me (b), Cl (c) and R^′=Me (4), Et (5), CH₂Ph (6)]. The structure in one case, Ru(Cl-aai-Et)₂(CA)] has been established by X-ray diffraction study. The π-π stacking and H-bonding network give a supramolecular ladder. All the complexes exhibit strong intense MLCT transition in the visible region and weak broad bands in higher wavelength (>700 nm). Visible transition (580-595 nm) shows negative solvatochromic effect. The cyclic voltammograms show two quasi-reversible to irreversible couples at positive to SCE and are due to CA⁻/CA²⁻ (1.2-1.4 V) and Ru(III)/Ru(II) (1.6-1.8 V) redox processes. Three couples negative to SCE are assigned to CA²⁻/CA³⁻ (−0.2 to −0.3 V) and azo reductions (−0.5 to −0.7, −0.8 to −0.9 V) of the chelated R-aai-R^′. The molecular orbital calculation (ZINDO/1, ZINDO/S) supports the spectral feature and electrochemical properties of the complexes.