Síntese e caracterização de complexos bipiridínicos de rutênio com ligantes polinitrilados

Abstract

In this work, the [Ru(bpy)(dcbpy)(TCNQ)Cl] and [Ru(bpy)(dcbpy)(TCNE)Cl] complexes, called Ru-TCNQ and Ru-TCNE, respectively, where bpy = 2,2’- bipyridine and dcbpy = 4,4’-dicarboxy-2,2’-bipyridine, were synthesized and characterized by spectroscopy and electrochemical techniques. The absorption spectra of the Ru-TCNQ and Ru-TCNE complexes showed bands assigned to metalto-ligand charge transfer transitions (MLCT). The luminescence spectra, with excitation at the MLCT, exhibited emission with maximum of intensity at 570 and 605 nm for the Ru-TCNQ and Ru-TCNE complexes, respectively. The luminescence decay of the complexes follows a biexponential law, with the Ru-TCNQ complex showing shorter lifetime than the Ru-TCNE complex. The infrared vibrational spectra of the complexes show a larger number of nitrile stretching bands, comparatively to the free ligands of coordination. These suggesting that the TCNX compounds are coordinated to the ruthenium atom. Upon coordenation, the shifts of these bands for lower energy values are indicative of the TCNX reduced form (TCNX⋅–). These results are confirmed by EPR spectra with g = 2.007 and 2.010 for Ru-TCNQ and Ru-TCNE complexes, respectively. The degree of charge transfer (Z) for the Ru-TCNQ and Ru-TCNE compounds was evaluated as 0.66 and 0.78, respectively. The RuIII/II redox potentials of the Ru-TCNQ (0.70V) and Ru-TCNE (1.30V) compounds, shifted for more positive potentials, when compared to the starting complex, cis- [Ru(dcbpy)(bpy)Cl2] (0,67V). These results inducate that the ligands acts as π-acceptor allowing a π-back-bonding interaction which imply in a thermodynamic stability of the metal in the reduced state (RuII). The data, all together, suggest that the TCNE compound presents a higher πback-bonding interaction capability than TCNQ compound.