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)A.