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 1H NMR measurements in 0.1 mol dm−3 Me4NCl aqueous solution at 298.1±0.1 K. The thermodynamic data suggest that the N4 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 P21/a, a=12.883(2) Å, b=12.259(3) Å, c=17.275(5) Å, β=108.65(2)°, V=2585.0(11) Å3, Z=4, R=0.0660, RW 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.