Inductive effect of methyl groups on acidopentaaminecobalt(III) complexes

Electron spectroscopy for chemical analysis (ESCA) was performed for [Co(NH3)(5)Cl](ClO4)(2), trans-[Co(NH3)(4)(NH2CH3)Cl]-(ClO4)(2), [Co(NH2CH3)(5)Cl] (ClO4)(2) and trans-[Co(NH3)(4)(NH2CH3) (OSO3)] (ClO4) complexes. Comparison of the results for the complexes [Co(NH3)(5)Cl](ClO4)(2) and trans-[Co(NH3)(4)(NH2CH3)Cl] (ClO4)(2) shows clearly the electronic influence (+I effect) of the methylamine group on the cobalt and through this on the chlorine atom in trans position. Comparison of [Co(NH2CH3)(5)Cl] (ClO4)(2) with trans-[Co(NH3)(4)(NH2CH3)Cl] (ClO4)(2) shows that methylation of the four cis-NH3 ligands does not produce a proportional decrease in the binding energy of the cobalt atom, while the electron density of the chloro ligand is not affected. For the complex trans-[Co (NH3)(4)(NH2CH3) (OSO3)] (ClO4) the +I effect is almost completely compensated by the presence of the sulfate group in trans position. Acid dissociation constants are also reported for [Co(NH3)(5)(OH2)](3+) and trans-[Co(NH3)(4)(NH2CH3) (OH2)](3+) ions. The implications of these results for the mechanism of the acid and base hydrolysis reactions of acidopentaaminecobalt(III) complexes are discussed. The preparation of the trans-[Co(NH3)(4)(NH2CH3) (OSO3)](ClO4) complex through the trans-[Co(NH3)(4)(NH2CH3) (SO3)](+) precursor is also described. (C) 2000 All rights reserved.