Complexation properties of a new macrocyclic polyaminic ligand (L) containing amidic pendant arms:: crystal structure of [PbL](ClO4)2

Synthesis and characterisation of the new macrocyclic ligand 1,7-dimethyl-4,10-di(methylcarbamoylmethy)-1,4,7,10-tetraazacyclododecane (L) are reported. The ligand, based on cyclen (1,4,7,10-tetraazacyclododecane), has been functionalised by the insertion of two methyl groups and two amidic pendant arms linked to the amine nitrogens. The interaction of L with H+, Na(I), Ca(II), Cu(II), Zn(II), Pb(II), and Gd(III) ions has been studied by potentiometric titrations, microcalorimetric and H-1 NMR measurements in 0.1 mol dm(-3) Me4NCl aqueous solution at 298.1 +/- 0.1 K. The thermodynamic data suggest that the N-4 Moiety is the binding site for Cu(II) and Zn(II), while in the case of Pb(II) also the pendant arms are coordinated to the metal ion. The crystal structure of [PbL](ClO4)(2) (space group P2(1)/a, a = 12.883(2) Angstrom, b = 12.259(3) Angstrom, c = 17.275(5) Angstrom, beta = 108.65(2)degrees, V = 2585.0(11) Angstrom(3), Z = 4, R = 0.0660, R-w(2) = 0.1467) shows the metal ion hexa-coordinated by the four nitrogen atoms of the cyclic tetra-amine and by the two amidic oxygens of the pendant arms. (C) 2001 Elsevier Science B.V. All rights reserved.