23523-25-3Relevant articles and documents
Cobalt(II) complexes with nitrogen donors and their dioxygen affinity in dimethyl sulfoxide
Comuzzi, Clara,Melchior, Andrea,Polese, Pierluigi,Portanova, Roberto,Tolazzi, Marilena
, p. 2194 - 2201 (2007/10/03)
The formation of CoII complexes with differently methylated N-donor ligands ethylenediamine (en), N,N′-dimethylethyl-enediamine (dmen), N,N,N′-trimethylethylenediamine (trmen), and N,N,N′,N′-tetramethylethylenediamine (tmen), has been studied at 298 K in both the aprotic solvent dimethyl sulfoxide (dmso) and in an ionic medium set to 0.1 mol dm-3 with Et4NClO4 under anaerobic conditions. UV/Vis spectrophotometric and calorimetric measurements were carried out to obtain the thermodynamic parameters for the systems investigated. Only mononuclear CoLj2+ complexes were formed (j = 1-3 for en, j = 1, 2 for dmen; and j = 1 for trmen and tmen) where the diamines act as bidentate agents. All the complexes are enthalpy-stabilized whereas the entropy changes counteract the complex formation. The results are discussed in terms of different basicities and steric requirements both of the ligands and the complexes formed. Voltammetric measurements were carried out to correlate the electrochemical properties of the anaerobic complexes with their different dioxygen affinities. The X-ray structure of the starting adduct [Co(dmso)6][ClO4]2, determined on a monocrystal, is also reported. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.
Magnetodynamic effects on outer-sphere electron-transfer reactions: A paramagnetic transition state
Ronco,Ferraudi
, p. 3961 - 3967 (2008/10/08)
The effect of the magnetic field on the rate of outer-sphere electron-transfer reactions has been investigated as a function of the field intensity, between 0 and 9 T, and at a given temperature. In complexes of d6 metal ions, i.e., Ru(II) and Co(III), the rate constant exhibits a complex dependence on the field: a complexity associated with field-induced changes of the electronic matrix element and the activation energy. Changes in the activation energy have been investigated as a function of the temperature at a given field intensity. These measurements have shown that the magnetic susceptibility of activation has the large positive values that are expected for a strongly paramagnetic transition state. The magnetic field effects are discussed in terms of symmetry-determined selection rules for the coupling of the initial and final electronic states of the reactions.
Potentiometric determination of the stabilities of cobalt(II) complexes of polyamine Schiff bases and their dioxygen adducts
Motekaitis, Ramunas J.,Martell, Arthur E.
, p. 2718 - 2724 (2008/10/08)
Potentiometric measurement of hydrogen ion concentration, previously employed for the determination of oxygenation constants of cobalt(II) complexes in aqueous and mixed aqueous solvents, is now extended to the determination of equilibrium constants for Schiff base ligands and for the determination of oxygenation constants for systems in which the ligands and/or their metal complexes are not completely formed in the absence of dioxygen or in the absence of the cobalt(II) ion. The method is illustrated by the potentiometric measurement of oxygenation constants for solutions in 70% dioxane-30% water (v/v) containing cobalt(II) chloride and the following ligarid components: 1, salicylaldehyde and N,N′-bis(2-aminoethyl)dipicolinic acid diamide; 2, salicylaldehyde and N,N-bis(2-aminophenyl)methylamine; 3, salicylaldehyde, ethylenediamine, and 4-methylpyridine; and 4, 3-fluorosalicylaldehyde, o-phenylenediamine, and 4-methylpyridine. The stability constant and dioxygen affinity are also reported for the cobalt(II) complex of a pentadentate ligand, N,N-bis(2-((2-hydroxybenzyl)amino)phenyl)methylamine, produced by hydrogenation of the Shiff base formed from salicylaldehyde and N,N-bis(2-aminophenyl)methylamine. The equilibrium parameters obtained provide all the information necessary to calculate the concentrations of all molecular species present in solution at 25.00°C and 0.100 M ionic strength as a function of p[H] and solution composition. The results are displayed for each system as distribution curves consisting of species concentration profiles vs p[H] at specific concentrations of solution components.
