Synthesis of 6,6 '-bis{methyl[1-(2-hydroxyethyl)piperazyl]}-2,2 '-bipyridine and its complexation with Co2+, Ni2+, Cu2+ and Zn2+ ions

6,6'-Bis{methyl[1-(2-hydroxyethyl)piperazyl]}-2,2'-bipyridine was synthesiz ed, and its complex formation equilibria with cobalt(II), nickel(II), coppe r(II) and zinc(II) ions were studied with potentiometric techniques over th e pH range 2.2-9.6 in 0.10 mol dm(-3) NaCl at 25 degrees C. The data indica te the formation of the species [M(HXLY)]((2+X)+) (X = 0-3 and Y = 1, 2) an d the hydrolysed [M(OH)(X)L]((2-X)+) complexes (X = 1, 2). All the metal io ns formed the [M(H2L)](4+) complexes, but Co-II and Zn-II also formed the [ M(H3L)](5+) complexes. The protonation of the ligand and the complex format ion were studied by H-1 NMR at 24 degrees C as well as by UV-VIS spectrosco py at 25 degrees C. These spectroscopic data, together with potentiometric results, can be used to discuss the conformational changes between the [M(H 3L)](5+) and the [M(H2L)](4+) complexes.