SPECIFIC FEATURES OF THE COMPLEXATION OF COPPER(II), MANGANESE(II), AND GADOLINIUM(III) WITH SALICYLIC, BENZOIC, AND SULFOSALICYLIC ACIDS IN AQUEOUS-SOLUTIONS OF NONIONIC SURFACTANT

The methods of potentiometric titration and NMR relaxation were used t o study the influence of the nonionic surfactant (NS), namely Triton X -100 (TX), on the acid-base and complexing properties of salicylic (H2 L), benzoic (HR), and sulfosalicylic (H3X) acids. The influence of NS added on the titration curves of the examined acids was analyzed and i t was established that salicylic and benzoic acids are bound by micell es to form species {H2L(TX)} and {HR(TX)} with logK equal to 2.12 +/- 0.03 and 1.57 +/- 0.03, respectively. The acidic properties of H3X are virtually the same in water and in the NS solutions. A significant (m ore than twofold) increase in the proton relaxation rate is observed i n the solutions of the mixtures of salicylic acid and TX in the presen ce of Cu2+, Mn2+, or Gd3+ ions. This effect was explained by the forma tion of ternary cation-ligand-surfactant species. For Cu(II) and Mn(II ), compounds {M(HL)(2)(TX)(2)} with logK equal to 0.90 +/- 0.04 and 1. 05 +/- 0.04, respectively, were detected. Complexes of composition {Gd (HL)(3)(TX)(2)} with logK = 0.22 +/- 0.05 were discovered for Gd(III). The ternary species of benzoic acid are formed only in the presence o f gadolinium: {GdR(TX)} with logK = -2.17 +/- 0.04. Sulfosalicylic aci d does not form such mixed NS-containing compounds with the cations ex amined.