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Outer‐Sphere Redox Reactions Leading to the Formation of Discrete Co III /Fe II Pyrazine‐Bridged Mixed‐Valence Compounds
Author(s) -
Bernhardt Paul V.,
Martínez Manuel,
Rodríguez Carlos
Publication year - 2010
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200900832
Subject(s) - chemistry , redox , pyrazine , valence (chemistry) , outer sphere electron transfer , electrochemistry , coordination sphere , crystallography , inner sphere electron transfer , stereochemistry , medicinal chemistry , inorganic chemistry , ion , crystal structure , organic chemistry , electrode
Abstract The kinetic and mechanistic study of the reaction of complexes [Co III XL] n + [X = Cl, OH, H 2 O; L = (NH 3 ) 5 , trans L 14 , trans L 14S , in which L 14 and L 14S are pentadentate macrocyclic ligands] with [Fe II (CN) 5 (pz)] 3– (pz = 1,4‐pyrazine) has been carried out as a function of the ligands, temperature and pressure. The results indicate that the previously established redox‐triggered formal substitution process (i.e., [Co III XL] n + + [Fe II (CN) 5 (pz)] 3– → {Co II L} + [Fe III (CN) 5 (pz)] 2– → [LCo II (pz)Fe III (CN) 5 ] → [LCo III (pz)Fe II (CN) 5 ]), which was found to be actuating for the reaction with [Fe II (CN) 6 ] 4– , also applies. The final mixed‐valence Class II complexes [LCo III (pz)Fe II (CN) 5 ] are formed whenever the {Co II L} moieties occurring after the initial outer‐sphere reduction are stable enough (L being macrocyclic encapsulating ligands), whereas decomposition from the {Co II L} + [Fe III (CN) 5 (pz)] 2– solution occurs for the pentaamino systems. The stability of the encounter complexes involved in the initial outer‐sphere redox process seems to play a crucial role in these processes. Fuoss ion pairing does not seem to apply and no correlation between the kinetic parameters and the redox potential for the reaction was found. The final stable mixed‐valence Class II compounds have been fully characterized in solution and their electrochemistry and UV/Vis characteristics agree with the expected trends. Nevertheless, both photochemistry and Fe II –N(pz) bond lability prevents their isolation as solids from the solutions purified by chromatography.