Synthesis and physical properties of ruthenium bipyridine complexes with TCNQ and TCNE ligands

[Ru(bpy)(dcbH2)(TCNQ)Cl] · (Ru–TCNQ) and [Ru(bpy)(dcbH2)(TCNE)Cl] · (Ru–TCNE) complexes, where bpy = 2,2’-bipyridine, dcbH2 = 4,4’-dicarboxy-2,2’-bipyridine, TCNQ = 7,7,8,8-tetracyano-p-quinodimethane, and TCNE = tetracyanoethylene, were synthesized and characterized by spectroscopic and electrochemical techniques. Comparatively to the TCNX ligands (TCNQ and TCNE) free of coordination, the infrared vibrational spectra of the complexes indicate that the coordination to the ruthenium atom occurs through only one nitrile group. Also, the downshift of these bands is indicative of the TCNX reduced form (TCNX-(TCNX-). This conclusion is reinforced by EPR spectra with g = 2.005 and 2.010 for the Ru–TCNQ and Ru–TCNE complexes, respectively. In addition, the structured absorption spectra observed for both complexes indicate that the TCNX moieties are coordinated as anion radicals, (TCNX-(TCNX-). Preliminaries luminescence studies indicate that the Ru–TCNX complexes present emission properties with reasonable lifetimes. The degree of charge transfer for the Ru–TCNQ and Ru–TCNE compounds was evaluated as 0.66 and 0.78, respectively. The RuIII/II redox potentials (Eox) for the Ru–TCNQ and Ru–TCNE complexes are observed, respectively, at 0.70 V and 1.30 V versus NHE. The data, all together, suggest that the TCNE species presents a higher charge uptake capability than TCNQ ligand.

The physical properties such as charge uptake, absorption, emission, and oxidation state of the TCNX ligands in the [Ru(bpy)(dcbH2)(TCNQ)Cl] and [Ru(bpy)(dcbH2)(TCNE)Cl] complexes, where bpy = 2,2′-bipyridine and dcbH2 = 4,4′-dicarboxy-2,2′-bipyridine, were investigated. The obtained results suggest not only the anion radical form, TCNX
• −, for the TCNX ligands upon coordination, but also that the TCNE species presents a higher charge uptake capability than TCNQ ligand.Figure optionsDownload as PowerPoint slide