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trans-Methylpyridine cyclen versus cross-bridged trans-methylpyridine cyclen. Synthesis, acid–base and metal complexation studies (metal = Co2+, Cu2+, and Zn2+)

Abstract : The synthesis of the cross-bridged cyclen CRpy2 {4,10-bis((pyridin-2-yl)methyl)-1,4,7,10-tetraazabicyclo[5.5.2]tetradecane}, a constrained analogue of the previously described trans-methylpyridine cyclen Cpy2 is reported. The additional ethylene bridge confers to CRpy2proton-sponge type behaviour which was explored by NMR and potentiometric studies. Transition metal complexes have been synthesized (by complexation of both ligands with Co2+, Cu2+ and Zn2+) and characterized in solution and in the solid state. The single crystal X-ray structures of [CoCpy2]2+, [CuCpy2]2+ and [ZnCpy2]2+ complexes were determined. Stability constants of the complexes, including those of the cross-bridged derivative, were determined using potentiometric titration data and the kinetic inertness of the [CuCRpy2]2+ complex in an acidic medium (half-life values) was evaluated by spectrophotometry. The pre-organized structure of the cross-bridged ligand imposes an additional strain for the complexation leading to complexes with smaller thermodynamic stability in comparison with the related non-bridged ligand. The electrochemical study involving cyclic voltammetry underlines the importance of the ethylene cross-bridge on the redox properties of the transition metal complexes.
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https://hal.univ-brest.fr/hal-01577019
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Submitted on : Thursday, August 24, 2017 - 4:08:58 PM
Last modification on : Friday, July 17, 2020 - 8:34:04 AM

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Nicolas Bernier, Judite Costa, Rita Delgado, Vítor Félix, Guy Royal, et al.. trans-Methylpyridine cyclen versus cross-bridged trans-methylpyridine cyclen. Synthesis, acid–base and metal complexation studies (metal = Co2+, Cu2+, and Zn2+) . Dalton Transactions, Royal Society of Chemistry, 2011, ⟨10.1039/C0DT01191F⟩. ⟨hal-01577019⟩

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