Capillary electrophoretic determination of coordination equilibrium constants of carboxylate ions with copper(II) complexed with several bis(1,10-phenanthroline) derivatives and bis(bipyridine) Original Research Article

A method for determining coordination equilibrium constants of some carboxylate ions (RCOO−) with Cu(II) complexed with phen (phen=1,10-phenanthroline), bpy (bpy=bipyridine), 4-methyl-, 5-methyl-, 5-chloro-, 5-nitro-, 4,7-dimethyl- and 5,6-dimethyl-phen was developed by capillary zone electrophoresis. The electrophoretic mobilities (μep) of [Cu(phen derivative)2]2+ and [Cu(bpy)2]2+ were obtained from the migration time of 3 μg ml−1 Cu(II) complexed with 1×10−3 mol dm−3 phen derivatives or bpy in the carboxylate buffers of pH 4.7 at 20 and 10 kV in the concentration range of ≦0.020 and >0.020 mol dm−3 carboxylate buffers, respectively. The μep value decreased with increasing the carboxylate concentration in the buffers. This indicates coordination of the carboxylate ion to [Cu(phen derivative)2]2+ or [Cu(bpy)2]2+. The typical first coordination equilibrium constants (KCuS1) of formate, acetate, propionate, n-butyrate, i-butyrate, n-valerate, and i-valerate ions for [Cu(phen)2]2+ were 620±80, 620±30, 1530±60, 540±40, 580±70, 560±30 and 380±20, respectively. All the second coordination equilibrium constants were near zero. Therefore, all the complexes formed the five-coordinating species, [Cu(phen derivative)2(RCOO)]+ and [Cu(bpy)2(RCOO)]+, in the aqueous carboxylate solutions.