Kinetic studies of the reduction of two ruthenium(III) complexes, mer-[RuCl3(dmso)(H2O)(tmtp)]center dot 2H(2)O (1) and mer,cis-[RuCl3(dbtp)(2)(dmso)] (2) (where dmso - dimethylsulfoxide, tmtp - 5,6,7-trimethyl-1,2,4-...
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Kinetic studies of the reduction of two ruthenium(III) complexes, mer-[RuCl3(dmso)(H2O)(tmtp)]center dot 2H(2)O (1) and mer,cis-[RuCl3(dbtp)(2)(dmso)] (2) (where dmso - dimethylsulfoxide, tmtp - 5,6,7-trimethyl-1,2,4-triazolo[1,5-a]pyrimidine and dbtp -5,7-ditertbutyl-1,2,4-triazolo[1,5-a]pyrimidine), by ascorbic acid were performed as a function of antioxidant concentration in acetate buffer within the pH range of 2.9-5. The rapid reduction of the ruthenium(III) complexes (1) and (2) resulted in the formation of the mer-[RuCl3(dmso)(H2O)(tmtp)](-) and mer,cis-[RuCl3(dbtp)(2)(dmso)]- ions and was followed by successive dissociation of the chloride ligands. The second-orderrateconstant (k(1)) for the reduction of the mer-[RuCl3(dmso)(H2O)(tmtp)]center dot 2H(2)O complex and the first-orderrateconstant for the hydrolysis of its reduced form were found to be 134 +/- 2 M-1 s(-1) and (3.8 +/- 0.9) x 10(-2) s(-1) at 25 degrees C and pH = 2.9, respectively. Similarly, the fast process assigned to the reduction of the mer,cis-[RuCl3(dbtp)(2)(dmso)] complex and the subsequent, slower process attributed to the hydrolysis of the cis-[RuCl3(dbtp)(2)(dmso)](-) ion were characterized by rateconstants of 145.5 +/- 0.8 M-1 s(-1) and (9 +/- 2) x 10(-3) s(-1) at 25 degrees C and pH = 2.9, respectively. Obtained data indicated that the reduction of the ruthenium(III) complexes strongly depends on pH and accelerates with increasing pH. The kinetic data indicates that the redox process followed an inner-sphere electron-transfer mechanism at pH higher than 3.
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