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, ac(2)[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 ac(2)[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 moldm-3 in NMe4NO3. The stability constants revealed that ac(2)[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 Cd2+ 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.



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Mateus, P; Li, F; Esteves, CV; Delgado, R; Brandao, P; Felix, V

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The authors acknowledge FCT, with co-participation of the European Community funds FEDER, POCI, QREN and COMPETE for the financial support under project PTDC/QUI/67175/2006. The NMR spectrometers used in the work are part of the National NMR Network and were purchased in the framework of the National Program for Scientific Re-equipment, contract REDE/1517/RMN/2005, with funds from POCI 2010 (FEDER) and FCT. The authors also thank M. C. Almeida for providing elemental analysis and ESI-MS data from the ITQB Elemental Analysis and Mass Spectrometry Service. P. M. thanks FCT for the grant SFRH/BD/36159/2007.

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