A new dioxadiaza macrocycle containing a rigid dibenzofuran group (DBF) and bearing two acetate pendant arms, ac(2)(DBF)N(2)O(2), has been synthesized in good yield by condensation of the parent macrocycle with potassium bromoacetate in basic aqueous solution. The protonation constants of ac(2)(DBF) N(2)O(2) and the stability constants of its complexes with Mn(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+) and Pb(2+) ions were determined at 298.2 K in aqueous solutions and at ionic strength 0.10 moldm-3 in NMe(4)NO(3). The stability constants revealed that ac(2)(DBF)N(2)O(2) has a higher affinity for larger metal ions, Cd(2+) and Pb(2+), showing a clear preference for cadmium. Spectroscopic data in solution and X-ray crystal structure determinations revealed that the higher affinity for Cd(2+) and Pb(2+) is due to the better fit of these metal ions into the macrocyclic cavity, derived from its ring size and rigidity and the involvement of all the donor atoms of the ligand in the coordination to these metal centres. Considering the negative effect of these heavy metal ions on human health and the environment, this study represents an important step in the development of selective chelators for these two pollutants.