Synthesis and characterisation of platinum(II) complexes of 1-methyl-2{(arylazo)imidazoles} and their dioxolene derivatives

1-Methyl-2-(arylazo)imidazoles, p-R-C6H4-N=N-C3H2 N-2-1-CH3, (RaaiMe (1); R = H(a), Me(b), Cl(c) have been treated with K2PtCl4 to synthesise brown-re d Pt(RaaiMe)Cl-2 (2) complexes. Addition of dioxolene in the presence of Et 3N to CHCl3-MeOH solution of Pt(RaaiMe)Cl-2 yield green coloured mixed comp lexes of the composition [Pt(RaaiMe)(O,O)] (O,O = catecholate (cat) (3); 4- tert-butylcateeholate (tbcat), (4); 3,5-di-tert-butylcatecholate (dtbcat), (5); tetracholorocatecholate (tccat). (6)). The complexes have been charact erised by elemental analyses, IR, UV-Vis-NIR and LH NMR spectral data. The solution electronic spectra exhibit ligand-to-ligand charge transfer (LLCT) transition at red to NIR region; the position and symmetry of the band dep end on the substituent type on the dioxolene and arylazoimidazole frames. T his is qualitatively assigned as HOMO(dioxolene)--> LUMO(RaaiMe). Cyclic vo ltammogram shows consecutive oxidation of catechols to semiquinone and semi quinone to quinone and azo reductions. The difference in first oxidation an d reduction potential is linearly related with LLCT transition energy. The comparison of the physical properties of present series of complexes with p alladium(II)-analogues show the involvement of Pt(II)-d pi orbitals to stab ilise the complexes.