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Article: Kinetics and mechanisms of the reduction of a cis-dioxoruthenium(VI) complex by [Ni(tacn)2]2+ and [Fe(H2O)6]2+

TitleKinetics and mechanisms of the reduction of a cis-dioxoruthenium(VI) complex by [Ni(tacn)2]2+ and [Fe(H2O)6]2+
Authors
Issue Date2002
Citation
Journal Of The Chemical Society, Dalton Transactions, 2002 n. 13, p. 2697-2701 How to Cite?
AbstractThe kinetics of the reduction of cis-[RuVIL(O)2]2+ (L = N,N,N′,N′-tetramethyl-3,6-dimethyl-3,6-diazaoctane-1,8-diamine) by [Ni(tacn)2]2+ (tacn = 1,4,7-triazacyclononane) and [Fe(H2O)6]2+ have been studied in aqueous acidic solutions. Both reactions have the following stoichiometry: 2MII + cis-[RuVIL(O)2]2+ + 2H+ → 2MIII + cis-[RuIVL(O)(OH2)]2+ (M = Ni or Fe). Two distinct steps were observed for both reactions and these are assigned to RuVI → RuV and RuV → RuIV. Both steps are first order in [RuVI] and [MII]. For the reduction by [Ni(tacn)2]2+, the activation parameters (I = [H+] = 0.1 mol dm-3) for the first step are ΔH‡ = 13.4 ± 1.0 kJ mol-1 and ΔS‡ = -111 ± 10 J mol-1 K-1; for the second reaction, ΔH‡ = 28.5 ± 1.5 kJ mol-1 and ΔS‡ = -110 ± 10 J mol-1 K-1. The rate constant for the first step is independent of acid concentration, an outer-sphere mechanism is proposed and a self-exchange rate of 2 × 104 dm3 mol-1 s-1 for the cis-[RuVIL(O)2]2+/cis-[RuVL(O) 2]+ couple is estimated using the Marcus cross-relation. The rate constant of the second step increases with [H+] and it reaches saturation at high [H+]. A mechanism involving a pre-equilibrium protonation of cis-[RuVL(O)2]+ followed by outer-sphere electron transfer is proposed. For the reduction by [Fe(H2O)6]2+, rate constants for both steps are independent of acid concentration in the range of pH = 1-3. The activation parameters (I = 1.0 mol dm-3, pH = 1.0) for the first step are ΔH‡ = 32.5 ± 1.5 kJ mol-1 and ΔS‡ = -52.5 ± 7 J mol-1 K-1; while for the second step, ΔH‡ = 17.3 ± 1.2 kJ mol-1 and ΔS‡ = -140 ± 13 J mol-1 K-1. An outer-sphere mechanism is proposed for the first step and an inner-sphere mechanism is proposed for the second step.
Persistent Identifierhttp://hdl.handle.net/10722/167727
ISSN
ISI Accession Number ID
References

 

DC FieldValueLanguage
dc.contributor.authorYau, SKWen_US
dc.contributor.authorChe, CMen_US
dc.contributor.authorLau, TCen_US
dc.date.accessioned2012-10-08T03:10:32Z-
dc.date.available2012-10-08T03:10:32Z-
dc.date.issued2002en_US
dc.identifier.citationJournal Of The Chemical Society, Dalton Transactions, 2002 n. 13, p. 2697-2701en_US
dc.identifier.issn1470-479Xen_US
dc.identifier.urihttp://hdl.handle.net/10722/167727-
dc.description.abstractThe kinetics of the reduction of cis-[RuVIL(O)2]2+ (L = N,N,N′,N′-tetramethyl-3,6-dimethyl-3,6-diazaoctane-1,8-diamine) by [Ni(tacn)2]2+ (tacn = 1,4,7-triazacyclononane) and [Fe(H2O)6]2+ have been studied in aqueous acidic solutions. Both reactions have the following stoichiometry: 2MII + cis-[RuVIL(O)2]2+ + 2H+ → 2MIII + cis-[RuIVL(O)(OH2)]2+ (M = Ni or Fe). Two distinct steps were observed for both reactions and these are assigned to RuVI → RuV and RuV → RuIV. Both steps are first order in [RuVI] and [MII]. For the reduction by [Ni(tacn)2]2+, the activation parameters (I = [H+] = 0.1 mol dm-3) for the first step are ΔH‡ = 13.4 ± 1.0 kJ mol-1 and ΔS‡ = -111 ± 10 J mol-1 K-1; for the second reaction, ΔH‡ = 28.5 ± 1.5 kJ mol-1 and ΔS‡ = -110 ± 10 J mol-1 K-1. The rate constant for the first step is independent of acid concentration, an outer-sphere mechanism is proposed and a self-exchange rate of 2 × 104 dm3 mol-1 s-1 for the cis-[RuVIL(O)2]2+/cis-[RuVL(O) 2]+ couple is estimated using the Marcus cross-relation. The rate constant of the second step increases with [H+] and it reaches saturation at high [H+]. A mechanism involving a pre-equilibrium protonation of cis-[RuVL(O)2]+ followed by outer-sphere electron transfer is proposed. For the reduction by [Fe(H2O)6]2+, rate constants for both steps are independent of acid concentration in the range of pH = 1-3. The activation parameters (I = 1.0 mol dm-3, pH = 1.0) for the first step are ΔH‡ = 32.5 ± 1.5 kJ mol-1 and ΔS‡ = -52.5 ± 7 J mol-1 K-1; while for the second step, ΔH‡ = 17.3 ± 1.2 kJ mol-1 and ΔS‡ = -140 ± 13 J mol-1 K-1. An outer-sphere mechanism is proposed for the first step and an inner-sphere mechanism is proposed for the second step.en_US
dc.languageengen_US
dc.relation.ispartofJournal of the Chemical Society, Dalton Transactionsen_US
dc.titleKinetics and mechanisms of the reduction of a cis-dioxoruthenium(VI) complex by [Ni(tacn)2]2+ and [Fe(H2O)6]2+en_US
dc.typeArticleen_US
dc.identifier.emailChe, CM:cmche@hku.hken_US
dc.identifier.authorityChe, CM=rp00670en_US
dc.description.naturelink_to_subscribed_fulltexten_US
dc.identifier.doi10.1039/B202230C-
dc.identifier.scopuseid_2-s2.0-0036019765en_US
dc.identifier.hkuros76378-
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-0036019765&selection=ref&src=s&origin=recordpageen_US
dc.identifier.issue13en_US
dc.identifier.spage2697en_US
dc.identifier.epage2701en_US
dc.identifier.isiWOS:000176467300019-
dc.identifier.scopusauthoridYau, SKW=26647235100en_US
dc.identifier.scopusauthoridChe, CM=7102442791en_US
dc.identifier.scopusauthoridLau, TC=7102222310en_US

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