OH^-存在下四苯基卟啉合钴氧化过程的电化学和光谱电化学

Electrochemistry, Spectroelectrochemistry of (TPP) Co in the Presence of OH- Anions

本文利用薄层伏安和现场光谱电化学方法考察了在EtCl_2中OH^-存在下四苯基卟啉合钴(TPP)CO~Ⅱ的电极氧化反应. 在低浓度OH^-存在下,(TPP)CO~Ⅱ与OH^-生成一配位的配合物(TPP)CO~Ⅱ(OH)^-,此配合物不可逆地被氧化为(TPP)CO~Ⅲ(OH)^-,氧化峰电位负移到0.53V,而卟啉环第一步氧化电位也负移到0.88 V.在高浓度OH^-存在下,(TPP)CO~Ⅱ(OH)^-氧化生成(TPP)Ca~Ⅲ(OH)_2^(2-),氧化电位随OH^-度增加向负移.卟啉环第一步和第二步氧化电位分别负移到0.57V和1.07V.同时观察到第二步氧化伴随后行化学反应,产物氧化电位在1.32V.测定了(TPP)CO~Ⅱ(OH)^-,(TPP)CO~Ⅲ(OH)^-和(TPP)Co~Ⅲ(OH)_2^(2-),(TPP)^+Co~Ⅲ(OH)^-和(TPP)^+Co^(Ⅲ)(OH)_2^(2-)各级配位化合物稳定常数.提出一个在OH^-滴定过程中(TPP)Co的各步配位反应及电化学反应的机理.

In the presence of OH- anions, electrochemical redox reactions of cobalt tetraphenylporphyrin (TPP)Go were investigated in EtCl2 solution by thin-layer eyclic voltammetry and spectroelectrochemistry. In the pressence of OH-, OH- was axially coordinated to (TPP) CoⅡ to generate (TPP)OoⅡ(OH)-. This complex was oxidized to (TPP) CoⅢ(OH)- at .E°' = 0.53 V (vs. SOE), The E°' for the first porphy-rin-ring oxidation was negatively shifted to 0.88V. When the amount of added OH-anions was more than two equivalent amount, no second OH- coordination reaction was found. Electrochemical oxidation reaction of (TPP)CoⅡ(OH)- generated (TPP)CoⅢ-(OH)22- species. The half-wave potential of this reaction was shifted negatively with increasing OH- concentration. The first and second porphyrin-ring oxidations occurred it E°' of 0.57V and 1.07V respectively. A chemical reaction following the second oxidation step was observed and a reversible redox step of the reaction product was observed at 1.32V. Mechanism for the coordination and elctrochemical reactions of (TPP) Co in the OH- titration process has been proposed. Stablity constants for (TPP) CoⅡ(OH)-, (TPP) OoⅢ(OH)-, (TPP) CoⅢ(OH)22-, (TPP)+- CoⅢ(OH)- and (TPP)+CoⅢ(OH)22- compiexes have been calculated.