STUDIES ON THE MIXED-LIGAND COMPLEXES OF COPPER(II) WITH GALLIC ACID AND PYRIDINE CARBOXYLIC-ACIDS AND THEIR BENZOLOGS

The ternary complex formation of copper(II) with gallic acid (gal) and 2-hydroxy nicotinic acid (hyna), 2-mercapto nicotinic acid (mena), salicylic acid (sa) or thiosalicylic acid (tsa) as a second ligand in a 1:1:1 molar ratio has been investigated in 40% (v/v) ethanol using spectrophotometric and pH titration methods. The solution equilibria of the ternary systems have been determined and the stability constants of the mixed complexes has been evaluated. Considering all parameters, the Cu-gal-sa ternary system was proved as a suitable, rapid, and sensitive spectrophotometric indicator for determining traces of copper. The ternary system containing sa obeys Beer's law up to 3.4 mu g.ml(-1) copper. The optimum range for the determination of copper (Ringbom) at pH 6.0 ranges from 0.63 to 1.74 mu g.ml(-1) of copper. The molar absorptivity of the ternary complex is 1.3 x 10(4) l.mol(-1).cm(-1).