Heavy-metal macrocyclic complexes: crystal and molecular structures of complexes of 1,5,9,13-tetra-azacyclohexadecane with Cd(NO3)2, HgCl2, PbCl2, and Pb(NO3)2

Abstract

Heavy-metal complexes of the sixteen-membered macrocycle, 1,5,9,13-tetra-azacyclohexadecane (L³), of formulae [Cd(L³)(NO₃)(H₂O)]NO₃·H₂O, [Hg(L³)Cl]₂[HgCl₄], [Pb(L³)Cl]Cl, and [Pb(L³)][NO₃]₂ have been prepared. Their structures were examined by ¹³C and ¹⁵N n.m.r. spectroscopy, and determined by X-ray crystallography which reveals a macrocycle cavity size which is most suitable for Hg²⁺co-ordination. In each compound all four macrocyclic N–H groups point to the same side of the macro-cyclic plane. The other ligands occupy trans positions for Cd²⁺(NO₃^– and H₂O) and Hg²⁺(Cl^–), but are in cis positions for the larger Pb²⁺. In [Pb(L³)Cl]⁺ the chloride ligand and the lone pair occupy adjacent positions on one side of the Pb²⁺ ion. With [Pb(L³)][NO₃]₂ the five independent molecules include one with two symmetrically bidentate NO₃^– groups, two with one bidentate and one unidentate, and two Pb atoms linked by two NO₃^– groups. Bond distance averages are Cd–N 2.334(6), Hg–N 2.38(3), Pb–N 2.54(1), Cd–O 2.413(8)–2.832(8), Hg–Cl 2.64(2)–2.83(2), Pb–Cl 2.98(1), and Pb–O 2.74(3)–3.17(4)Å.