Uni- and Bivalent First-Row Transition Metal Ions

Substitution at axial sites in metalloporphyrins and phthalocyanins is important in the context of their behavior as models for biological systems and for their potential catalytic properties. The reaction of imidazole (Him) with phthalocyaninatoiron(II) in DMSO has been reinvestigated and shows two distinct relaxation processes as shown in Eq. (2) and (3). Forward rate constants were kif=9.8 0.2x 10 s , k2f= 5.4 + 0.15 s  

The rate of dissociation of the glycinate ligands in [Co(II)(gly)3] have been measured in pulse radiolysis experiments with conductimetric detection. The hydrated electrons generated in a solution of tris(glycinato)Co(III) by the electron pulse reduce some of the complex to 

In tetraazamacrocyclic Co(II) complexes, the formation of / -peroxo-Co(III) complexes following coordination of O2 to Co(II) complexes can be suppressed if the macrocycle is functionalized to inhibit face-to-face approach of the Co(II) centers. The thermodynamic stabilities of complexes [(X)LCo] (X =SCN or Q , L = C-meso-5,7,7,12,14,14-hexamethyl-l,4,8,ll-tetraaza-cyclotetradecane) have been determined and the effects of the anion X on the rate of dioxygen binding have been studied by laser flash photolysis after the flash, there is an immediate bleaching of the solution at the absorbance wavelength of the complex, followed by a slower return of absorbance. Reestablishment of the equilibrium for SCN can be analyzed in terms of Eq. (4) to (6) an analogous sequence applies when the anion is Cl . 

Few five-coordinate complexes have been the subject of kinetic study. The anation kinetics of the five-coordinate macrocyclic complex [Co(tmc)(H20)] (tmc = l,4,8,ll-tetramethyl-l,4,8,ll-tetraazacyclotetra-decane) by OCN , SCN , and Nf have been measured by stopped flow spectrophotometry. The environment of the tetramethyl cavity is clearly critical in the properties and reactivity of such complexes pX of the coordinated solvent is about an order of magnitude lower than a range of other Co(II) aquo complexes and this is attributed to the hydrophobic nature of the tetramethyl cavity. Ligand substitution can proceed through a 1 1 ion pair, where the entering ligand is above the tetramethyl cavity, and also via a tram 

1 2 outer-sphere complex, where another anion is associated on the opposite side of the tetraaza plane. While the reactivity order of H2O, OCN , SCN , and parallels their basicity for both pathways, the crowding of the methyl groups reduces the effective discrimination of the entering ligand to around a factor of seven. 

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Ligand Substitution on Complexes of Uni- and Bivalent First-Row Transition Metal Ions... 

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