Synthesis, characterization and thermodynamics of some novel tertiary phosphine cobalt(III) unsymmetrical tetradentate Schiff Base complexes

The [Co(salpyren)PBu3]ClO4 center dot H2O, [(N-salicylidene-N'-pyrrolidene)-1,2-ethylenediaminato]tributylphosphine-Co(III) perchlorate monohydrate; [Co(Mesalpyren)PBu3]ClO4 center dot H2O, [(7-methyl-N-salicylidene-N'-pyrrolidene-)1,2- ethylenediaminato] tributylphosphineCo( III) perchlorate monohydrate; [Co(Phsalpyren)PBu3]ClO4 center dot H2O [(7-phenyl-N- salicylidene-N'-pyrrolidene)-1,2-ethylenediaminato] tributylphosphineCo(III) perchlorate . monohydrate, were synthesized and characterized. The equilibrium constants and the thermodynamic parameters were measured spectrophotometrically for the 1:1 adduct formation of [Co(chel)PBu3]ClO4 center dot H2O, where (chel = salpyren, Mesalpyren, Phsalpyren) as acceptors with phosphites [ P( OR) 3 ( R = Me, Et and i-Pr)] as donors, in acetonitrile (CH3CN) and dimethylformamide (DMF) solvents, in constant ionic strength (I = 0.1 M NaClO4) and at various temperatures T = 283 to 313 K. The trend of the equilibrium constants of the donors (phosphites) toward a given cobalt( III) Schiff base complex is as follows: P(OEt)(3) > P(Oi- Pr)(3) > P(OMe)(3). The trend of the equilibrium constants of the cobalt(III) Schiff base complexes toward a given phosphite is as follows: 7-Mesalpyren > salpyren > 7-Phsalpyren. The trend of the equilibrium constants with a given donor toward a given acceptor with respect to the solvent is as follows: CH3CN > DMF.