Inductive effect of methyl groups on acidopentaaminecobalt(III) complexes

Abstract

Electron spectroscopy for chemical analysis (ESCA) was performed for [Co(NH 3) 5Cl](ClO 4) 2, trans-[Co(NH 3) 4(NH 2CH 3)Cl](ClO 4) 2, [Co(NH 2CH 3) 5Cl](ClO 4) 2 and trans-[Co(NH 3) 4(NH 2CH 3)(OSO 3)](ClO 4) complexes. Comparison of the results for the complexes [Co(NH 3) 5Cl](ClO 4) 2 and trans-[Co(NH 3) 4(NH 2CH 3)Cl](ClO 4) 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(NH 2CH 3) 5Cl](ClO 4) 2 with trans-[Co(NH 3) 4(NH 2CH 3)Cl](ClO 4) 2 shows that methylation of the four cis-NH 3 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(NH 3) 4(NH 2CH 3)(OSO 3)](ClO 4) the +I effect is almost completely compensated by the presence of the sulfato group in trans position. Acid dissociation constants are also reported for [Co(NH 3) 5(OH 2)] 3+ and trans-[Co(NH 3) 4(NH 2CH 3)(OH 2)] 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(NH 3) 4(NH 2CH 3)(OSO 3)](ClO 4) complex through the trans-[Co(NH 3) 4(NH 2CH 3)(SO 3)] + precursor is also described.