CHARACTERISTIC BEHAVIOR OF THE COMPLEXATION OF COPPER(II) WITH POLYMER-BOUND VINYLIMIDAZOLE LIGANDS

Some polymer ligands of N-vinylimidazole-co-N-vinylpyrrolidone (Plm) having different mole fractions of N-vinylpyrrolidone have been prepared. Successive formation constants for the complexation of Cu-II with these Plms in aqueous solutions have been determined by means of spectrum deconvolution at pH 3.5. The present results demonstrate that the successive formation constants are given by K-1=[CuL]/[Cu][L], K-2= [CuL(2)]/[CuL], K-3= [CuL]/[CuL(2)] and K-4 = [CuL(4)]/[CuL(3)] (charge omitted, L = imidazole residue on Plm). The results clearly indicate that the concentration ratio, [CuL] : [CuL(2)] : [CuL(3)] : [CuL(4)], is largely constant for a given Pim when the concentration of imidazole residues is varied. The values of K-2, K-3 and K-4 decrease with increasing mole fraction of vinylpyrrolidone residues (VPRo) in the Plms. The successive formation constants increase in the order K-2 < K-3 < K-4 for poly(N-vinylimidazole), whereas the reverse (i.e. K-2 > K-3 > K-4) is found for Plm with a VPRo mole fraction of 0.8. Above this VPRo mole fraction, CuL(4) species are rarely formed. These results also suggest that the distributions of Cut, species in Cu-II-Plm solutions can be controlled by adjusting the content of VPRo in the Plm.