Spectroelectrochemistry of Anthraquinone-2-CO2-ReI(CO)3(2,2´-bipyridil) and related complexes

E.WOLCAN, M.R.FÉLIZ, G.RUIZ, M.P. JULIARENA AND R.O.LEZNA

São Pedro -SP- Brazil

Congreso; 54th Annual Meeting of the International Society of Electrochemistry; 2003

Luminicent probes such as anthraquinone (AQ) complexes are interesting materials in relation to their application to non-polar microenviroments such as biopolymers (DNA, etc.) [1] Experimental Acetonitrile, CAN, for spectroscopy, Merck UVASOL, was dried over activated alumina for several days. Potencial were measured against the Ag/ AgCl electrode and are quoted w.r.t the Fc/Fc+ couple. The procedure was found to be suitable for electrochemistry in the -2.5/ +0.6 v potencial range. Bu4NPF6 was dried al 140C for at least 24 hs. Pt and Au discs, polished to a mirror finish, were used as working electrodes. In situ UV-Visible spectra were taken as described elsewhere [2]. Results and Discussion Ac voltammetry experiments were conducted on AnQ-CO2-ReI(CO)3(2,2’-bpy) in Pt/ ACN/ Bu4NPF6 solutions at 6 Hz. The current response fig !, shows three reversible waves at -1.24 V, -1.67 V and -1.77 V, the background being featureless. Reductions at -1.24 V and -1.67 V take place at the anthraquinone ligand whereas the process at -1.77 V is based at the 2,2’–bipiridyl, bpy, molecule. With a view to identifying the species electrochemically generated, spectra were taken each 50 mV on a slow cathodic scan, 5 mVs-1, between -0.43 V and -2.4 V, the reference being the spectrum at -0.43 V where no absorption was detected. Fig 2 exhibits, for clarity a reduced set of spectra. Bands observed as from -1.28V at 583 nm and 420 nm stem from the product of the AQ ligand first reduction, the AQ.- anion radical. It is worth noticing the same spectrum is obtained when excited AQ*, probably in triplet state, is reduced by triethyl amine ( reductive quenching) [3 ]. As the potencial is changing into more negative values, a new band at 494 nm shows up as from -1.63 V indicating AQ.- is undergoing a further reduction to give AQ2-. The bpy ligand undergoes reduction at -1.77 V to give bpy.- attend by the appearance of weak bands whith absorption at 585 nm, 520 nm and 365 nm. These absorptions, that are not clearly defined in Fig. 2, will be displayed with enhanced sensitivity as potencial modulated spectra in the presentacion. An interesting result to be analized is the similarity between the bpy.- ligand spectrum, obtained in an electrochemical environment and the absorption of BrRe(CO)3(bpy)- generated by reductive quenching with triethanolamine of BrRe(CO)3(bpy)*, triplet state, formed, in turn, by flash photolysis [4]. Photochemical/ photophysical measurements on the complex as well as other relationships between spectroscopic and electrical variables will be presented and discussed.   References 1-     B. Armitage, C.J. YU, C. Dand G.B. Schuter, J. Am. Chem. Soc. 116 (1994) 9847. 2-     R. O. Lezna, S. Juanto, J. H. Zagal, J. Electroanal. Chem, 389 (1-2) (1995) 197; R. O. Lezna, An Asoc. Quim. Argent. 82 (4) (1994) 293. 3-     G. T. Ruiz, M. P. Juliarena, R. O. Lezna, E. Wolcan, M. R. Feliz and G. Ferraudi, Helvetica Chimica Acta 85 (2002) 1261. 4-     C. Kutal, M.A. Weber, G. Ferraudi and D. Geiger, Organometallics, 4 (1985) 2161. 5-     E. Wolcan, M.R. Feliz, G.T. Ruiz, M. P. Juliarena and R. O. Lezna, J. Electroanal.  Chem 533 (2002) 101.