Octahedral cobalt(III) complexes of the chloropenta-ammine type. Part XI. The preparation, properties, and reactions of some chloroaminebis(ethylenediamine)cobalt(III) salts containing unidentate aminoalkanols as influencing ligands

Abstract

The synthesis of an isomeric series of salts of the type [Co en₂L Cl]²⁺ is described (en = ethylenediamine, L = ethanolanine or 2- and 3-hydroxypropylamine. Based on evidence of visible and i.r. absorption spectra, the complexes are assigned a cis configuration, with the ligands L occupying one co-ordination position through nitrogen. The rate constants for appearance of chloride ions from aqueous solutions have been determined and Arrhenius parameters calculated. The products observed are the corresponding aquo cations, [Co en₂L H₂O]³⁺, but the reaction involves a rate-determining internal attack on cobalt by an oxygen lone-pair in the ligand L, forming an intermediate [Co en₂L]³⁺ in which L acts as a chelate. This is then followed by a rapid one-ended displacement of chelate by water to give the final product. The rate constants for base hydrolysis have also been determined at 0° and ionic strength of 0·1M. This reaction involves a rapid pre-equilibrium formation of an ion-pair, {[Co en₂L Cl]²⁺ OH^–}, followed by a rate-determining dissociation of the chlorine, whose position is then taken up by the hydroxide ion.