RATES OF ELECTRON-TRANSFER FROM OSMIUM(II) TO IRON(III) COMPLEX-IONS CONTAINING 2,2'-BIPYRIDINE OR ITS DERIVATIVES AS LIGANDS - EFFECTS OF ELECTROLYTES AT LOW CONCENTRATIONS AND REACTANT-SEPARATION DISTANCE
RATES OF ELECTRON-TRANSFER FROM OSMIUM(II) TO IRON(III) COMPLEX-IONS CONTAINING 2,2'-BIPYRIDINE OR ITS DERIVATIVES AS LIGANDS - EFFECTS OF ELECTROLYTES AT LOW CONCENTRATIONS AND REACTANT-SEPARATION DISTANCE
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DOI：
10.1021/j100272a049
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发表时间：
1985-12-19
影响因子：
--
通讯作者：
WAHL, AC
中科院分区：
文献类型：
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作者：
BRAGA, TG;WAHL, AC
用停流法测定了在乙腈中，在极低的反应物和电解质浓度下，OsL'32+向FeL 33+（L和L'代表2，2 '-联吡啶或其衍生物）的电子转移速率。电解质浓度、温度和配体是变化的。此外，Evalues的反应研究确定从电化学电池电动势测量。用电导法研究了低浓度FeL_（3A）_2和CoL_（3A）_3（A ′分别代表PF_（6 ~）或C_（10）<f）与具有相同配体的大配位阳离子之间的离子缔合作用。未发现2：1电解质离子缔合的证据，但大多数3：1电解质存在一定的缔合。将离子缔合视为由于离子对形成而产生的，C104-的形成常数KA是PF 6-的形成常数KA的~ 3倍。阴离子对电子转移反应的催化作用是OsL ~（32+）与FeL ~（3-A ~（2+））离子对快速反应的结果。离子对与C104-或PF 6-的反应速率大致相同; C104-是更好的催化剂，因为FeL 33+与C104-的缔合更大。采用Bransted-Bjerrum处理和Debye-Hilckel活度系数修正，从OsL ~（32+）与FeL ~（33+）、FeL ~（3-PF ~（62+））或FeL ~（3-Cl ~（42+）反应三个途径定量解释了电子转移比速率随电解质浓度的变化。KA和a0的值，离子的最接近的距离，从电导数据的分析中获得。比速率随温度变化很小;对于裸离子路径，阿克里尼乌斯活化能Eact = 0.7±1.1 kcal mol-1，对于离子对路径，Eact = 3.6±1.5 kcal mol-1。与L= L ′ = 4，4 ′-二甲基-2，2 ′-联吡啶的反应的ε值在25 - 40 ℃的温度范围内为0.224±0.002 V，与上述L ′和与L= 4，4 ′-二苯基-2，2 ′-联吡啶的反应的ε值在25 ℃下为0.127±0.005 V。的Marcus-Sutin模型的基础上，涉及硬球反应在一个连续的，不饱和的电介质中，测量的速率常数与理论估计的比较表明，最好的协议是通过使用最小的反应器分离距离。这一观察表明，电子转移
The rates of electron transfer from OsL'32+ to FeL33+, L and L'representing 2, 2'-bipyridine or its derivatives, havebeen measured by the stopped-flow method at very low reactant and electrolyte concentrations in acetonitrile. Electrolyte concentrations, temperature, and ligands were varied. Also, Evalues for the reactions investigated were determined from electrochemical-cell emf measurements. Conductance measurements at low concentrations of FeL'3A2 and CoL3A3, A'representing PF6~ or C10< f, were made to investigate ion association between PF6~ or C10< f and large complex cations having the same ligands as the reactants. No evidence was found for ion association of the 2: 1 electrolytes, but some association occurs for most 3: 1 electrolytes. Treating ion association as being due to ion-pair formation gives formation constants, KA, for C104~ that are~ 3 times those for PF6". Catalysis of the electron-transfer reactions by anions is the result of rapid reaction of OsL'32+ with ion pairs, FeL3-A2+. Ion pairs with C104~ or PF6" react atabout the same rate; C104" is the better catalyst because of the greater association of FeL33+ with C104 “. The changes in specific rates of electron transferwith electrolyte concentration are interpreted quantitatively by considering three paths, reaction of OsL'32+ with FeL33+, FeL3-PF62+, or FeL3-CI042+, and using the Bransted-Bjerrum treatment with Debye-Hilckel activity-coefficient corrections. Values of KA and a0, the distance of closest approach of ions, were obtained from analysis of the conductance data. Specific rates varied little with temperature; for the bare-ion path the Arrhenius activation energy,£ act= 0.7±1.1 kcal mol" 1 and for the ion-pair paths£ act= 3.6±1.5 kcal mol" 1. The£ value for the reaction with L= L'= 4, 4'-dimethyl-2, 2'-bipyridine is 0.224±0.002 V in the temperature range from 25 to 40 C, and£= 0.127±0.005 V at 25 C for the reaction with L'as above and with L= 4, 4'-diphenyl-2, 2'-bipyridine. Comparison of the measured rate constants with theoretical estimates based on the Marcus-Sutin model, involving hard spheres reacting in a continuous, unsaturated dielectric medium, shows that the best agreement is obtained by using minimum reactant-separation distances. This observation indicates that electron transfer