Kinetic and thermodynamic studies of aquation reactions in [RuL2(mac)](q+) complexes: [mac=1,4,8,11-tetraazacyclotetradecane (cyclam) or 1,4,7,10-tetraazacyclododecane (cyclen); and L=Cl-, OH-, OH2]

摘要

We report here the synthesis, characterization and kinetic studies of [RuL2(mac)](n+) complexes [mac=1,4,8,11-tetraazacyclotetradecane (cyclam) or 1,4,7,10-tetraazacyclododecane (cyclen); and L=Cl-, OH-, OH2]. The dichloride complexes release one Cl- producing [RuCl(L)(mac)](n+) or two Cl- producing [Ru(L)(2)(mac)](n+) (L=OH2, OH-) in aqueous solution within pH 1-7. The product of these reactions were characterized by ultraviolet-visible (UV-Vis) spectroscopy. The chloride affinity of Ru(III) depends on the macrocyclic ring size and geometric structure. The k(1) and thermodynamic activation parameters (at pH 4.4, T=25 degrees C) of cis-[RuCl2(cyclen)](+) complex are k(1)=3.6x10(-3)s(-1) (25 degrees C); H-#=40.2kJmol(-1) and S-#=-138JKmol(-1); under similar conditions, for cis-[RuCl2(cyclam)](+) these values are 2.4x10(-3)s(-1), H-#=50.8kJmol(-1) and S-#=-119JKmol(-1). The rate of chloride aquation reactions for cis-[RuCl2(cyclen)](+) is about 1.5 times faster than for the cyclam complex. The reactivity difference could be due to a combination of the sigma-trans effect, the nephelauxetic effect and the effect of solvation.