On the discriminating and stability increasing properties of Alizarin maroon in mixed-ligand complexes of Yttrium(3)

The stability constants of the yttrium(3) mixed ligand complexes (1:1:1) containing alizarin maroon (azm) and as a second ligand salicylic acid (sa), 5-sulphosalicylic acid (ssa), 5-nitrosalicylic acid (nsa), 2,2'-bipyridyl (bipy) and 1,10-phenanthroline (phen) have been determined potentiometrically in 20% (v/v) ethanol-water medium (I 100 mmoldm-3 NaClO4, 25±0,10C). The complexation equilibria of the different biligand systems were demonstrated. All of these mixed-ligand complexes are considerably more stable than expected from purely statistical reasons. The results obtained were discussed in relation to the nature of the secondary ligands involved. For the equilibrium, Y(azm)2+Y(L)2 rightleftdblarrow 2Y(azm)(L), the following constants, log X, were determined: Y(azm)(sa) 3,11 (0,46); Y(azm)(ssa) 2,76 (0,33); Y(azm)(nsa) 3,02 (0,48); Y(azm)(bipy) 3,96 (0,99); Y(azm)(phen) 4,33 (1,07). The constants given in parentheses correspond to Δlog KY [log KY(azm)Y(azm)(L)-log KYY(L)]. (Author)