Thermal Stability of [N, N′-Bis (2-hydroxyimino-l-methylpropylidene)1, 3-propanediaminato] bis (aniline)cobalt(III) Complexes, [Co(Hbhpn)B3₂]X₂, in the Solid State

Abstract

The kinetics of aniline liberation-anation reaction of [Co(Hbhpn)B₂]X₂ complexes {H2bhpn=N, N′-bis(2-hydroximino-1-methylpropylidene)-1, 3-propanediamine; B =aniline or its derivatives; X=Cl^-, Br^-, or I^- ion} have been studied in the solid state by the Coats-Redfern method on the basis of the thermogravimetry in nitrogen stream [Co(Hbhpn)B₂]X₂→[CoX₂(Hbhpn)] +2B↑.

The values of the rate constant and the activation energy (E_a) determined from the slopes of the straight lines in the plots of log [-log (1-α)/2.303.T²] vs 1/T, suggested that the above reaction follows the SN 1 mechanism. The values of the activation energy and the frequency factor were 150-188 kJ.mol^-1 and 10¹⁷-10²¹ s-^-1, respectively, for aniline liberationanation reactions. These E_a values were considered to reflect mostly the strength of the Co(III)-axial ligands (aniline derivatives) bonding. Furthermore, the enthalpy changes ΔH caused by the liberation-anation reaction of the [Co(Hbhpn)B₂]X₂ complexes were found to be about 2 times larger than those observed for analogous [Co(Hdmg)₂B₂]X complexes, where H₂dmg is dimethylglyoxime.