Abstract
Some cobalt(III) complexes with a potentially tetradentate unsymmetrical NNOS Schiff base ligand have been synthesized and characterized using IR, 1HNMR, UV-Vis spectroscopy and elemental analysis. The equilibrium constants were measured spectrophotometrically for 1:1 adduct formation of the cobalt(III) complexes with some cyclic amines in acetonitrile as solvent at constant ionic strength (I = 0.1 M NaClO4), and at various temperatures. In addition, the ground state geometries of the complexes were optimized using density functional theory (DFT) at B3LYP/6-311G** level. Binding energy, thermodynamic parameters, structural parameters and electronic structures of complexes are investigated. The theoretical investigations were done for comparing with the experimental results. Our comparison between the computational and experimental results revealed that the cobalt(III) complexation process is spontaneous, exothermic and entropically unfavorable.
Highlights
Synthetic oxygen carriers are of great interest as models to mimic oxygen caring metalloenzymes[1] and oxygenases, such as hemoglobin and cytochrome P-450,2 which play important roles in the catalytic oxygenation mechanism of organic substrates.[3]The Schiff base ligands and their complexes represent one of the most widely utilized classes of ligand in synthetic oxygen carrier compound
The Co(III) Schiff base complexes have been extensively used to mimic cobalamin (B12) coenzymes,[5] dioxygen carriers and oxygen activators and for enantioselective reduction.[6]. These complexes are an important class of coordination compounds because being interesting B12 models and due to their interesting magnetic properties, spectroscopic characteristics and catalytic aspects.[7]
In contrast six-coordinate complexes undergo dissociative ligand substitution reaction. The study of their behavior is of fundamental importance to the understanding of complex formation and ligand substitution reaction in general. Base on this experience and in order to contribute to a better understanding of the properties of five and six coordinated cobalt(III) Schiff base complexes, we report here the synthesis and characterization of some novel apparently five-coordinated complexes with apical tertiary phosphines as complex [Co(Chel)(PBu3)]+ where Chel: methyl-2-{N-[2-(acetone)ethylidynenitrilo]ethyl}amino1-cyclopentenedithiocarboxylate, methyl-2
Summary
Synthetic oxygen carriers are of great interest as models to mimic oxygen caring metalloenzymes[1] and oxygenases, such as hemoglobin and cytochrome P-450,2 which play important roles in the catalytic oxygenation mechanism of organic substrates.[3]. The Schiff base ligands and their complexes represent one of the most widely utilized classes of ligand in synthetic oxygen carrier compound. This usually arises from their structural similarity to those found in biological systems.[4]. The Co(III) Schiff base complexes have been extensively used to mimic cobalamin (B12) coenzymes,[5] dioxygen carriers and oxygen activators and for enantioselective reduction.[6] These complexes are an important class of coordination compounds because being interesting B12 models and due to their interesting magnetic properties, spectroscopic characteristics and catalytic aspects.[7] Co(III). A comparison between the calculated results (structure, formation constant, thermodynamic parameter) and experimental results are used to validate the conclusions
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