Kinetic Studies of the Electron Transfer Reaction in Iron(II) and Iron(III) Systems. III. Complex Formation and Catalytic Action with Thiocyanate Ion in Dimethyl Sulfoxide
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概要
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The formation constants <I>K</I><SUB>1</SUB> and <I>K</I><SUB>2</SUB> of the complexes Fe(NCS)<SUP>2+</SUP> and Fe(NCS)<SUB>2</SUB><SUP>+</SUP> in dimethyl sulfoxide (DMSO) and the rate constants and the activation parameters of the electron transfer reaction between Fe(II) and Fe(III) in DMSO catalyzed by thiocyanate ion were measured. <I>K</I><SUB>1</SUB> and <I>K</I><SUB>2</SUB> are (8.4±0.9)×10<SUP>2</SUP> M<SUP>−1</SUP> and (0.97±0.10)×10<SUP>2</SUP> M<SUP>−1</SUP> at μ=0.1 M and 25°C, respectively. The apparent rate constant <I>k</I><SUB>app</SUB> is nearly independent of acid concentrations and increases markedly with total thiocyanate ion concentration. The rate constants <I>k</I><SUB>1</SUB>and <I>k</I><SUB>2</SUB> of Fe<SUP>2+</SUP>-Fe(NCS)<SUP>2+</SUP> and Fe<SUP>2+</SUP>-Fe(NCS)<SUP>2+</SUP> systems are (2.24±0.35)×10<SUP>2</SUP> M<SUP>−1</SUP>sec<SUP>−1</SUP> and (2.96±0.64)×10<SUP>3</SUP> M<SUP>−1</SUP> sec<SUP>−1</SUP> at μ=0.2 M and 25°C, respectively. <I>ΔH</I><SUB>1</SUB><SUP>\neweq</SUP>=8.9±1.0 kcal/mol and <I>ΔS</I><SUB>1</SUB><SUP>\neweq</SUP>=−17±3 cal/deg·mol are obtained from the temperature dependence of <I>k</I><SUB>app</SUB>. From a comparison with the data of cases catalyzed by Cl<SUP>−</SUP> and SCN<SUP>−</SUP> ions in water and DMSO, the present electron transfer reaction is deduced to proceed probably <I>via</I> the inner-sphere mechanism with the SCN<SUP>−</SUP> ion as a bridging ligand, similar to the Cl<SUP>−</SUP> ion-catalyzed reaction in DMSO.
- 公益社団法人 日本化学会の論文
著者
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Yoshizawa Noriko
Department Of Pediatrics Saitama Kyodo Hospital
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Sakamoto Yoko
Department of Chemistry, Nara Women s University
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Wada Goro
Department of Chemistry, Nara Women s University
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Wada Goro
Department of Chemistry, Faculty of Science, Nara Women s University
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Yoshizawa Noriko
Department of Chemistry, Nara Women s University
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