Binary and ternary complexes of cobalt(II) with some polydentate ligands

Potentiometric investigations on binary and ternary complexes of Co2+ ion with multidentate ligands; 1,3-dihydroxy-4-(2'-pyridylazo) benzene (PAR, H2L); 1-(2'-arsonophenylazo)-2-hydroxynaphthalene-3,6-disulphonic acid (APANS, H5L); pyrogallol sulphonaphthalene (PGR, H4L) and the pair of ligands; PAR-ethylenediamine (en, A), PAR-1: 10-phenanthrolene (pn, A), APANS-en, APANS-pn, PGR-en, PGR-pn have been made in aqueous solution at 20degreesC and at an ionic strength of 0.1 M KNO3. The analysed experimental data indicate existence of CoHL+, CoHL(OH), CoL(OH)(-), Co(HL)(2), COHL2, CoL2-, CoHLA(+) (with PAR, en and pn); CoLA (OH)(-) (with PAR and en)' CoH2L-, CoHL2-, CoL3-, CoH(2)LA(-), CoHLA(2-) (with APANS, en and pn), CoLA(3-) (with APANS and en); CoL2-, CoLA(2-) (with PGR, en and pn) species in steps. Equilibrium constants of these probable complex species have been evaluated and the structures have been discussed.