Properties of metal complexes of a new dioxadiaza macrocycle containing a dibenzofuran unit and acetate pendant arms

A new dioxadiaza macrocycle containing a rigid dibenzofuran group (DBF) and bearing two acetate pendant arms, ac2[17](DBF)N2O2, has been synthesized in good yield by condensation of the parent macrocycle with potassium bromoacetate in basic aqueous solution. The protonation constants of ac2[17](DBF)N2O2 and the stability constants of its complexes with Mn2+, Ni2+, Cu2+, Zn2+, Cd2+ and Pb2+ ions were determined at 298.2 K in aqueous solutions and at ionic strength 0.10 mol dm-3 in NMe4NO3. The stability constants revealed that ac2[17](DBF)N2O2 has a higher affinity for larger metal ions, Cd2+ and Pb2+, 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 Pb2+ 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. A new diaza crown ether containing a dibenzofuran group and two acetate pendant arms has been prepared. Our results revealed that this compound has a higher affinity for larger metal ions, Cd2+ and Pb2+,with a clear preference for cadmium. It was shown that this unusual selectivity pattern is governed by the ring size and rigidity of the macrocycle. Note: Some of the scientific symbols cannot be represented correctly in the abstract. Please read with caution and refer to the original publication