In this work, the thermodynamics of some other cobalt (III) Schiff base complexes with different ligands and the solvent effect have been examined. Comparison of their properties, spectrally and thermodynamically, aimed to investigate the effects of different electronic and steric situations.
Co(5-nitroSalen)(PBu 3 )]ClO 4 ·H 2 O and [Co(Salpd)(PBu 3 )]ClO 4 ·H 2 O were synthesized and characterized. The stability constants and the thermodynamic parameters were measured spectrophotometrically for 1:1 adduct formation of [CoL(PBu 3 )]ClO 4 ·H 2 O, (L = Salen, 5-nitroSalen, Salpd), and [Co(Salen)(PMe 2 Ph)]ClO 4 ·H 2 O as acceptors with P(OR) 3 (R = Me, Et, i-Pr) as donors, in acetonitrile solvent and in constant ionic strength (I = 0.01 M) and at various temperatures. The trend of the reactivity of cobalt(III) Schiff-base complexes with PBu 3 axial ligand toward a given donor is as follows: 5-nitroSalen > Salen > Salpd. Also, the following reactivity trend of the donors toward a given cobalt(III) Schiff-base complex is in the operation: P(O-i-Pr) 3 > P(OEt) 3 > P(OMe) 3 . Résumé : On a effectué la synthèse et on a caractérisé les complexes suivants: [Co(5-nitroSalen)(PBu 3 )]ClO 4 ·H 2 O et [Co(Salpd)(PBu 3 )]ClO 4 ·H 2 O. Faisant appel à des méthodes spectrophotométriques, on a mesuré les constantes de stabilité et les paramètres thermodynamiques pour la formation d'adduits 1:1 entre les complexes accepteurs [CoL(PBu) 3 ]ClO 4 ·H 2 O dans lesquels L = Salen, 5-nitroSalen et Salpd et [Co(Salen)(PMe 3 Ph)]ClO 4 ·H 2 O et les P(OR) 3 (dans lesquels R = Me, Et, i-Pr) comme accepteurs, dans l'acétonitrile comme solvant, à force ionique constante (I = 0,01 M) et à diverses températures. La tendance de la réactivité des complexes des bases de Schiff du cobalt(III) avec le ligand PBu 3 axial est donnée par la séquence suivante: 5-nitroSalen > Salen > Salpd.Du côté des donneurs vis-à-vis d'un complexe donné d'une base de Schiff du cobalt(III), la tendance est exprimée par la séquence suivante: P(O-i-Pr) 3 > P(OEt) 3 > P(OMe) 3 .
The complexes: [Co(BAE)(PEt 3 )]ClO 4 . H 2 O(BAE 5 bis(acetylacetone)ethylenediimine) and [Co(BBE)(PR 3 )]ClO 4 . H 2 O, (BBE 5 bis(benzoylacetone)ethylenediimine and R 5 Et, Bu),were synthesized and characterized. The equilibrium constants and the thermodynamic parameters were measured spectrophotometrically for 1 : 1 adduct formation of [Co(chel)L]ClO 4 . H 2 O, (where chel 5 BAE, BBE and L 5 PBu 3 , PEt 3 and PMe 2 Ph) as acceptors and P(OR) 3 (R 5 Me, Et and Ipr) as donors, in acetonitrile in constant ionic strength (I 5 0.01M Et 4 NClO 4 ) and at various temperatures T 5 293 to 313 K. The trend of the equilibrium constants of five coordinate cobalt(III) Schiff base complexes toward a given phosphite donor according to the axial ligand is as follows: PMe 2 Ph > PBu 3 % PEt 3 . Also, the trend of the equilibrium constants of the donors (phosphite) toward a given cobalt(III) Schiff base complex is as follows: P(OEt) 3 > P(OIpr) 3 > P(OMe) 3 . The trend of the equilibrium constants of cobalt(III) Schiff base complexes with respect to the Schiff bases used in this research is as follows: BBE > BAE.
Three Co(III) complexes of the type [Co(chel)(PBu3)]ClO4.H2O, (chel = 5-BrSalen, 5-MeOSalen and 4-MeOSalen), were synthesised and characterised by elemental analysis, IR, UV-Vis and 1H NMR spectroscopy. In their electronic spectra, the absorptions between 550 and 750 nm of these complexes are attributable to the lowest d–d transition. The axial ligands affect this transition through a σ-intraction with the dz2 orbital and the equatorial ligands affect it by π-interaction with populated d-orbitals. On the basis of an electronic structural model, in which the dz2 orbital is populated in forming cobalt(II), it is suggested that equatorial ligand substitution affects the reduction potentials less than axial ligand substitution.
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