Journal
INORGANIC CHEMISTRY
Volume 52, Issue 9, Pages 5138-5153Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ic400015v
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Funding
- Fundacao para a Ciencia e a Tecnologia (FCT)
- European Community fund FEDER [PTDC/QUI/67175/2006]
- European Community fund POCI [PTDC/QUI/67175/2006]
- European Community fund QREN [PTDC/QUI/67175/2006]
- European Community fund COMPETE [PTDC/QUI/67175/2006]
- National Program for Scientific Re-equipment [REDE/1517/RMN/2005]
- FCT [PEst-OE/EQB/LA0004/2011]
- CNRS
- University of Burgundy
- Conseil Regional de Bourgogne through the 3MIM Project
- French Ministry of Research
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Two cross-bridged cyclen-based macrocycles with two trans-N-acetic acid arms, one having a dibenzofuran (DBF) moiety as the bridge, H(2)L1, and the other a diphenyl ether (DPE) one, H(2)L2, were synthesized. Both compounds behave as proton sponges. The thermodynamic stability constants for the Cu2+, Zn2+, Al2+, and Ga3+ complexes of both compounds were determined. They exhibit an excellent thermodynamic selectivity for copper(II), ensuring that metal ions largely present in the human body do not interfere with the copper(H) chelates. All complexes are very slow to form, and [CuL2] and [CuLl] are extremely inert to demetallate, especially [CuL2]. The acid-assisted dissociation of [CuLl] led to a half-life of 4.28 h in 5 M HCl at 363.2 K, while [CuL2] needed harsher conditions of 12 M HCl at 363.2 K with a half-life of 308 days. To the best of our knowledge, [CuL2] exhibits the highest half-life value for a copper(II) complex of a polyazamacrocycle derivative reported in the literature until now. Single crystal X-ray diffraction determined for [Cu(H(2)L1)](ClO4)(2) showed the copper center in a distorted octahedral environment bound to the N4O donors of the macrobicyde and one oxygen atom from a carboxylic arm, while for [CuL2] it showed the copper center in a trigonal bipyramid geometry only bound to the donors of the macrobicycle and leaving the carboxylate arms away from the coordination sphere. UV-vis-NIR and X-band EPR spectra showed that in [CuLl] the copper center adopts a distorted compressed octahedral environment, which is the only structure found in solution for this complex, while in [CuL2] a similar environment was found in the first stages of its slow formation but reached a square-pyramidal geometry upon stabilization. The acetate arms play therefore an important role during the formation of the complex, as revealed by the comparison of its complexation behavior with the corresponding parent compounds.
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