Synthesis, spectral characterization and electrochemical studies of mixed-ligand complexes of platinum(II) with 2-(arylazo)pyridines and catechols. Single-crystal X-ray structure of dichloro {2(phenylazo) pyridine}platinum(II)

The reaction of 2-(arylazo)pyridines, RH4C6N=NC5H4N (aap, 1 where R=H (pap) , p-Me (p-tap), p-Cl (p-Clpap)) with K2PtCl4 in 1:2 boiling acetonitrile-wa ter affords orange-red complexes of the type Pt(aap)Cl-2 (2). The IR spectr um shows two v(Pt-Cl) stretches suggesting cis-PtCl2 configuration. The str uctural confirmation was carried out by an X-ray diffraction study of Pt(pa p)Cl-2 (2a). The addition of catechols to a chloroform-methanol solution of Pl(aap)Cl-2 in the presence of Et3N yielded green colored mixed-ligand com plexes of the formula Pt(aap)(O,O) (O,O = catecholate (cat) (3), 4-tert-but ylcatecholate (tbcat), (4), 3,5-di-tert-butylcatecholate (dtbcat) (5) and t etrachlorocatecholate (tccat) (6)). The complexes were characterized by ele mental analyses, IR, W-Vis-NIR and H-1 NMR spectral data. Electronic spectr a exhibit a ligand-ligand charge transfer (LLCT) transition at NIR region; the position and symmetry of the band depend on the type of substituent on the catechol frame. This is qualitatively assigned as 3b(1)(cat)-->pi*(aap) transition. Cyclic voltammogram of the complexes show four successive redo x responses: two couples positive to SCE are referred to as oxidation of ca techol to semiquinone and semiquinone to quinone, respectively and two coup les negative to SCE correspond to azo reductions. (C) 2001 Elsevier Science B.V. All rights reserved.