Thermodynamic Study of Cobalt(III) Schiff Base Complexes in Mixed EtOH/H 2 O

The [Co(Chel)(PBu₃)]ClO₄.H₂O(Chel = dsp, mdsp and ndsp, where dsp = N,N′-disalicylidene-1,2-phenylene diamine, mdsp = 4-methyl-N,N′-disalicylidene-1,2-phenylene diamine and ndsp = 4-nitro-N,N′-disalicylidene-1,2-phenylene diamine), were synthesised and characterised. The equilibrium constants and the thermodynamic parameters of these complexes as acceptors with PBu₃, were measured spectrophotometrically for 1: 1 adduct formation in various mixed EtOH/H₂O and constant ionic strength (I = 0.1M NaClO₄) and at various temperatures T = 288–308 K. The trend of the reactivity of five coordinate Co(III) Schiff base complexes toward PBu₃ donor according to the Schiff base ligand is mdsp > dsp > ndsp. The trend of the reactivity of a given Co(III) Schiff base complexes towards PBu₃ donor according to the water/ethanol mole fractions is 0.12 > 0.36 > 0.52 > 0.64.