Cyclen derivatives with two trans-methylnitrophenolic pendant arms: a structural study of their copper(II) and zinc(II) complexes


Two new cyclen derivatives, H(2)do2nph and H(2)cb-do2nph, containing two trans-2-methyl-4-nitrophenol pendant arms and the latter including also an ethylene cross-bridge, were prepared in good yields using the bisaminal synthetic route. The two ligands were studied comparatively regarding their metal complexation behaviour. The copper(II) and zinc(II) complexes of H(2)do2nph and H(2)cb-do2nph were studied in dimethylsulfoxide-water (9 : 1 v/v) solution by a range of spectroscopic techniques. Copper(II) complexes were also studied in solid state by X-ray single crystal diffraction. These studies showed that the copper(II) and zinc(II) complexes of H(2)do2nph exhibited a distorted square pyramidal coordination environment with the four nitrogen atoms of the cyclen ring defining the basal plane, and that one of the nitrophenolate arms did not coordinate to the metal, independently of its protonation state. On the other hand, depending on the protonation state of one of the nitrophenolic arms, the cross-bridged derivative forms copper(II) complexes with distorted square pyramidal or octahedral geometries with one or two arms coordinated to the metal centre, respectively. In the complex with distorted octahedral geometry, the two phenolic oxygen atoms are coordinated to the metal centre in a cis-fashion. Acid-assisted dissociation assays in 1 mol dm(-3) HCl DMSO-H2O (9 : 1 v/v) solution at 298.2 K allowed one to determine the half-life of both copper(II) complexes, which is lower for the derivative without a cross-bridge as expected, while for the other one it is quite high and in line with similar cross-bridged cyclen derivatives from the literature.



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Esteves, CV; Lima, LMP; Mateus, P; Delgado, R; Brandao, P; Felix, V

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The authors acknowledge Fundacao para a Ciencia e a Tecnologia (FCT), with co-participation of the European Community funds FEDER, POCI, QREN and COMPETE, for the financial support and the fellowship of C. V. Esteves under project PTDC/QUI/67175/2006. P. Mateus and L. M. P. Lima acknowledge FCT also for the postdoctoral fellowships SFRH/BPD/79518/2011 and SFRH/BPD/73361/2010, respectively. The NMR spectrometers 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. We also acknowledge M. C. Almeida for providing elemental analysis and ESI-MS data from the ITQB/IBET Analytical Services Unit.

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