NMR spectroscopic and potentiometric study on complexation thermodynamics of some N,N '-bis(2-hydroxyethyl)piperazine complexes

The complex formation equilibria between N,N'-bis(2-hydroxyethyl)piperazine and alkaline-earth(II), praseodymium(III), nickel(II), copper(II) and zinc (II) ions were studied with potentiometric techniques over the pH range 2.4 -9.6 in 0.10 mol dm(-3) NaCl at 25 degrees C. The data indicate the formati on of the species [ML](2+/3+), [M(HL)](3+/4+) and the hydrolysis of copper( II) (aq). The protonation of the ligand was also studied by H-1 NMR spectro scopy in 0.10 mol dm(-3) NaCl (aq) at 24 degrees C. These data, together wi th C-13{H-1} NMR spectroscopic data, indicate equatorial-equatorial and equ atorial-axial conformations of 2-hydroxyethyl side chains with respect to t he six-membered piperazine ring. The ring inversion of the piperazine ring was studied by H-1 NMR spectroscopy in 1:1 (v:v) acetone-methanol solution over the temperature range 40 to -90 degrees C.