Arylazoimidazoles (RaaiH,p-R-C₆H₄N=N-C₃H₃N₂, R=H, Me, OMe, Cl and NO₂) are N,N′-chelators. On reaction with (NH₄)₂[OsCl₆], two classes of isomers blue-violetctc-Os(RaaiH)₂Cl₂ and red-violetccc-Os(RaaiH)₂Cl₂ have been isolated. The complexes have been characterised by elemental analyses, IR, UV-Vis and¹H NMR spectral data. The N=N stretching is red shifted by 70–80 cm⁻¹ compared to the free ligand values and indicatesd(Os)→π*(azo) charge shifting. This is supported by MLCT transition in the visible region.¹H NMR spectra suggest that blue-violet isomers areC₂-symmetric and red-violet isomers areC₁-symmetric. Redox studies show the Os(III)/(II) couple of both isomers at 0·6–0·7 Vvs SCE and two successive azo reductions.

Dechlorination of Ru(PPh₃)₂(TaiMe)Cl₂ (TaiMe = p-Me-C₆H₄-N=N-C₃H₂NN(1)-Me (1), 1-methyl-2-(p-tolylazo)imidazole) has been carried out in acetone solution by Ag⁺ and reacted with N,N’-chelators to synthesise [Ru(PPh₃)₂ (TaiMe)(N,N’)]²⁺. The complexes have been isolated as their perchlorate salts. The N,N’ chelators are 1-alkyl-2-(phenylazo)imidazoles (PaiX, X = Me, Et, CH₂Ph); 2-(arylazo)pyridines, (Raap,p-R-C₆H₄-N=N-C₅H₄N; R = H, Me, Cl); 2-(arylazo)pyrimidines (Raapm,p-R-C₆H₄-N=N-C₃N₂H₂; R = H, Me, Cl); 2,2’-bipyridine (bpy) and 1,10-phenanthroline (o-phen). Unsymmetrical N,N’ chelators may give two isomers and this is indeed observed. The¹H NMR spectral data refer to the presence of two isomers in the mixture in different proportions. With consideration of coordination pairs in the order of PPh₃, PPh₃; N,N (N refers to N(immidazole)) and N’,N (N’ refers to N(azo)), the complexes have been characterised astrans-cis-cis andtrans-trans-trans configuration; the former predominates in the mixture. Electrochemical studies exhibit high potential Ru(III)/Ru(II) couple and quasireversible N=N reduction. Electronic spectra show high intensity (ε ∼ 10⁴) MLCT transition in the visible region (520 ±10) nm along with a shoulder (ε ∼ 10³) in the longer wavelength region.