Study on the complex formation of cobalt chelates with polymer ligands

Abstract

AbstractVariously composed copolymers from styrene and 4‐vinylpyridine (4‐VP) were prepared and their complex formation reactions with benzylbis(dimethylglyoximato)Co(III) [BzCo(III)(DMG)2] and N,N′‐ethylenebis(salicylideneiminato)Co(II) (Co(II)salen) were studied kinetically by the stopped‐flow rapid scanning spectroscopy. For the complex formation reaction with BzCo(III)(DMG)2, the relationship between the complex formation constant K and the content of 4‐pyridylethylene units in the copolymers showed an unusual bell‐type curve, and the K values were higher than the K value of complexation with pyridine. From the correlation between K, k (complex formation rate constant), and k′ (complex dissociation rate constant), it resulted that (1) the higher K values of the polymer systems are due to the lower k′ values compared with the pyridine system, and (2) the bell‐type change of the K values is also caused by the k′ values. In the case of Co(II)salen‐copolymer systems, two species of the complex, i.e., mono‐ and diaxial coordinated complexes were clearly identified by spectrometric kinetics, whereas the pyridine system gave only a mono‐axial coordinated complex. The diaxial coordination seems to lead to a much more favorable structure than the monoaxial one, due to the entropic gain or to the polymer chelate effect.