KINETICS OF SOLVENT WATER EXCHANGE ON IRON(III)
KINETICS OF SOLVENT WATER EXCHANGE ON IRON(III)
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DOI：
10.1021/ic50215a014
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发表时间：
1981-01-01
影响因子：
4.6
通讯作者：
JORDAN, RB
中科院分区：
文献类型：
--
作者：
GRANT, M;JORDAN, RB
本文用脉冲核磁共振方法测量了氧-17在铁（Ⅲ）（8.20 × 10 ~（-3）-0.315m）和高氯酸（0.34- 3.89m）水溶液中从0 ℃到140 ℃的横向和纵向弛豫速率。用此结果确定了Fe（OH_2）_（63）~+和Fe（OH_2）_5 OH_2 ~+的溶剂水交换动力学参数。对于Fe（OH 2）63+和Fe（OH 2）63+，k（s-1，25 ℃）、AH*（kcal mol-1）和AS*（cal mol-1 deg* 1）的值分别为（1.6 × 0.2）× 102、15.3 × 0.6和2.9 × 1.6。1)Fe（OH_2）_5（OH）_2 ~+的X_（10）5、10.14 × 0.35和1.26 × 0.95。溶剂交换速率和各种配体取代速率与Fe（OH 2）6 3+的缔合活化和Fe（OH 2）5（OH）2+的解离活化最为一致。确定配体取代金属离子机理的标准方法是比较溶剂交换速率和配体取代速率。[2]在对离子对进行校正后，我们发现，至少对于钴（II）和镍（II），Eigen和Wilkins提出的离解机理与实验结果最为一致。已经有一些关于铁（III）配体取代的研究，但由于缺乏公开的水交换速率数据，其机理结论仍然不确定。Fe（OH 2）63+离子水解和聚合的容易性使铁（III）系统复杂化。本文报道了氧-17脉冲核磁共振弛豫时间测量的结果，在水溶液中的铁（III）高氯酸溶液。水溶剂交换速率的温度和氢离子依赖性已被确定。
Pulsed NMR methods have been used to measure the transverse and longitudinal relaxation rates of oxygen-17 in aqueous solutions of iron (III)(8.20 X 10-3—0.315 m) and perchloric acid (0.34-3.89 m) from 0 to 140 C. The results havebeen used todetermine the kinetic parameters for solvent water exchange from Fe (OH2) 63+ and Fe (OH2) 5OH2+. The values of k (s'1, 25 C), AH*(kcal mol" 1), and AS*(cal mol" 1 deg* 1) are (1.6 ą 0.2) X 102, 15.3 ą 0.6, and 2.9 ą 1.6 for Fe (OH2) 63+ and (1.2 ą0. 1) X 105, 10.14· 0.35, and 1.26 ą 0.95 for Fe (OH2) 5 (OH) 2+. Thesolvent exchange rates and various ligand substitution rates are most consistent with associative activation for substitution on Fe (OH2) 63+ and dissociative activation for Fe (OH2) 5 (OH) 2+.A standard method of determining the mechanism of ligand substitution on a metal ion is to compare the solvent exchange rate with the ligand substitution rate. 2 After correction for ion pairformation it has been found, at least forcobalt (II) and nickel (II), that the dissociative mechanismsuggested by Eigen and Wilkins3 is most consistent with the results. There have been a number of studies of ligand substitution on iron (III), but the mechanistic conclusions remain uncertain because of the lack of published water exchange rate data. The iron (III) system is complicated by the ease with which the Fe (OH2) 63+ ion hydrolyzes and polymerizes. This paper reports the results of oxygen-17pulsed NMR relaxation time measurements on aqueous iron (III) perchloric acid solutions. The temperature and hydrogen ion dependence of the water solvent exchange rate has been determined.