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

Abstract

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 ( μ ep) 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 μ ep 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 ( K CuS1) 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.