Binary and Ternary Complexes of Cobalt(II) with Some Polydentate Ligands

Abstract

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 20^oC 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, CoL^2-, CoHLA⁺ (with
PAR, en and pn); CoLA (OH)^- (with PAR and en)' CoH₂L^-,
CoHL^2-, CoL^3-, CoH₂LA^-, CoHLA^2- (with APANS, en and pn),
CoLA^3- (with APANS and en); CoL ^2-, CoLA^2- (with PGR, en and
pn) species in steps. Equilibrium constants of these probable complex
species have been evaluated and the structutes have been discussed.