Kinetics and mechanism of complex formation between <em>cis-</em>(ammine )-(3-NO₂^- salicylato)bis( ethylenediamine)cobalt(III) ion with aluminium(III) in aqueous medium

Abstract

The kinetics of reversible formation of the binuclear complex between <em>cis</em>-[Co(en)₂(NH₃)O₂CC₆H₃(3-NO₂)OH]²⁺ and AI(III) has been investigated at 20-35&deg;C, <em>I</em> = 0.1 mol dm^-3, [AI(III)] = 0.003-0.009 mol dm^-3 and <em>p</em>H = 2.26 to 3.21. Comparison of the rate data with those for the pentammine cobalt(III) analogue indicates rate acceleration for both the formation and dissociation of the binuclear species which discounts the possibility of chelate ring formation and opening as the rate limiting steps. The activation enthalpy and entropy for the spontaneous dissociation of the binuclear species are 117 &plusmn; 3 kJ mol^-1 and 98 &plusmn; 9 JK^-1 mol^-1 respectively. These values are in keeping with dissociative interchange mechanism.