Preparation, characterization and complexation of 4,6-dimethyl-1,3-bis{methyl-[1-(2-hydroxyethyl) piperazyl]}benzene and 2,6-di{methyl-[1-(2-hydroxyethyl)piperazyl]}pyridine

摘要

4,6-Dimethyl-1,3-bis{methyl[1-(2-hydroxyethyl)piperazyl]}benzene (L-1) and 2,6-di-{methyl[1-(2-hydroxyethyl)piperazyl]}pyridine (L-2) were synthesized and their complex formation equilibria with alkaline-earth(II), Pr-III, Ni-II, Cu-II and Zn-II ions were studied with potentiometric techniques over the pH range 2.1-9.3 in 0.10 mol dm(-3) NaCl at 25 degrees C. The data indicate that whereas L-1 forms only [ML](2+/3+) complexes, L-2 forms [M(HXLY)]((2+X)+) (X = 0-2, Y = 1,2) and the hydrolysed [M(OH)(X)L](1+/0) (X = 1, 2) transition-metal(II) complexes. With Pr-III L-2 forms only [M(HL)](4+) and [M2L2](6+) complexes. L-2 contains the pyridine unit and is a much better complexing agent than L-1. The protonation of the ligands was studied by H-1 NMR in aqueous solution of 0.10 mol dm(-3) NaCl at 24 degrees C, L-2 crystallizes in, a monoclinic space group P2(1)/a, a = 9.998(2), b = 15.476(3), c = 12.957(3) Angstrom, beta = 92.64(2)degrees, The ligand shows a planar structure. Upon complexation, however, the 1-(2-hydroxyethyl)piperazine fragments may rotate around the bonds: C15-C17 and C10-C11 by ca. 180 degrees to create a pocket containing three nitrogen donor atoms the orientation of which is suitable for the coordination with metal ions. [References: 34]