Electrochemical properties of a ruthenium complex immobilized as thin films and in carbon paste electrodes

The electrochemical properties of mer-[RuCl3(dppb)(4-pic)] (dppb = Ph2P(CH2)4PPh2, 4-pic = CH3C5H4N), Rupic, in CHCl3 are governed by the formation of species such as [Ru2Cl5(dppb)2], [Ru2(dppb)2Cl4(4-pic)] and trans-[RuCl2(dppb)(4-pic)2] upon the reduction of “[RuCl2(dppb)]”. The overall behavior depends on whether Rupic is immobilized in cast or Langmuir-Blodgett (LB) films, or incorporated into a carbon paste electrode (CPE). In cyclic voltammograms, one redox process appears for LB/Rupic films and CPE/Rupic, at Epa = 0.35 V, Epc = 0.25 V vs SCE, and Epa = 0.32 V, Epc = 0.24 V vs Ag/AgCl, respectively. This redox process was ascribed to the RuIII/RuII charge transfer. For cast films the redox pair was poorly defined, with Epa = 0.27 V and Epc = 0.20 V. The reason for the difference lies in the phase separation and formation of aggregates onto ITO for the cast film, in contrast to the LB film. With aggregation, the formation of species occurring in solution is impaired for Rupic in cast films. The electrochemical properties for Rupic in LB films and incorporated into CPE allowed the electrocatalytic activity of Rupic to be exploited in sensors for dopamine and ascorbic acid.