Formation of cobalt, nickel and copper complexes with murexide in ethanol-water mixtures.

The complexation reactions between murexide and Co(2+), Ni(2+) and Cu(2+) in C(2)H(5)OH-H(2)O mixtures have been investigated spectrophotometrically. The formation constants of the 1:1 complexes formed increase in the order Co(2+) < Ni(2+) < Cu(2+) for all solvent mixtures studied, and log K(f) is a linear function of the mole fraction of ethanol. The heat of complexation was determined calorimetrically for the nickel and copper complexes. The values of DeltaH degrees and DeltaS degrees are solvent-dependent, and all three complexes have negative DeltaH degrees and positive DeltaS degrees values.