Synthesis, characterization and kinetic studies of the cis-[RuCl2(cyclen)]+ complex

We report here the synthesis, characterization and kinetic studies of cis-[RuCl2(cyclen)]+ in aqueous solution, where cyclen is the macrocyclic ligand 1,4,7,10-tetraazacyclododecane. The complex releases one Cl− producing cis-[RuCl(OH)(cyclen)]+ in aqueous solution at pH 4.60. The product of this reaction was characterized by Ultraviolet–Visible (UV–Vis) spectrum in comparison to the synthesized cis-[RuCl(OH)(cyclen)](BF4)·2H2O. The electrochemical data showed that Epc of the Ru(III/II) peak increases as the macrocycle ring size decreases and also when the trans conformation is changed to cis. The chloride affinity of Ru(III) depends on the macrocycle ring size since cis-[RuCl2(cyclam)]+ (cyclam=1,4,8,11-tetraazacyclotetradecane) does not release chloride for at least 12 h. The overall effect between cyclam and cyclen reflects the fact that the electron involved in the reduction enters a nonbonding π-d orbital and its energy is affected by the macrocyclic ligand.