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.