Synthesis, electrochemical characterization and potentiometric titration of trans-[RuCl2(L)(4)] complexes (L = pyridine derived ligands: 3-pyridinecarboxylic acid and 4-pyridinecarboxylic acid)

In this work we report the synthesis, spectroscopic characterization, poten tiometric titration and electrochemical studies performed on trans-[RuCl2(n ic)(4)] (I) and trans[RuCl2(i-nic)(4)] (II) complexes, where nic=3-pyridine carboxylic acid and i-nic=4-pyridinecarboxylic acid. The complexes were syn thesized using a ruthenium blue solution as a precursor in the synthetic ro ute, and characterized by electronic spectroscopy, vibrational FT-IR spectr oscopy, and H-1 and C-13 NMR. The results indicated a trans geometry. Cycli c voltammetry performed in water/acetone (I:1)solution revealed a quasi-rev ersible process centered on the Ru(II) species and a dependence of the redo x potential, E-1/2. On the pH. The electronic spectra showed that the MLCT bands were also affected by the pH, undergoing a hypsochromic shift (blue s hift) as the pH increased. The spectroelectrochemical analysis indicated th at the bands in the visible region progressively faded as new UV bands emer ged during the oxidation process. The equilibrium constants for trans-[RuCl 2(nic)(4)] and trans-[RuCl2(i-nic)(4)] were determined by potentiometric ti tration, indicating that protonic species dominated at pH values lower than 2.6, whereas non-protonic species dominated at pH values higher than 5.0.