American Chemical Society
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Halide and Nitrite Recognizing Hexanuclear Metallacycle Copper(II) Pyrazolates

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posted on 2011-02-07, 00:00 authored by Ahmed A. Mohamed, Simone Ricci, Alfredo Burini, Rossana Galassi, Carlo Santini, Gina M. Chiarella, Doris Y. Melgarejo, John P. Fackler
Halide-centered hexanuclear, anionic copper(II) pyrazolate complexes [trans-Cu6((3,5-CF3)2pz)6(OH)6X], X = Cl, Br, I are isolated in a good yield from the redox reaction of the trinuclear copper(I) pyrazolate complex [μ-Cu3((3,5-CF3)2pz)3] with a halide source such as PPh3AuCl or [Bu4N]X, X = Cl, Br, or I, in air. X-ray structures of the anion-centered hexanuclear complexes show that the six copper atoms are bridged by bis(3,5-trifluoromethyl)pyrazolate and hydroxyl ligands above and below the six copper atom plane. The anions are located at the center of the cavity and weakly bound to the six copper atoms in a μ6-arrangement, Cu−X = ∼3.1 Å. A nitrite-centered hexanuclear copper(II) pyrazolate complex [trans-Cu6((3,5-CF3)2pz)6(OH)6(NO2)] was obtained when a solution of [PPN]NO2 in CH3CN was added dropwise to the trinuclear copper(I) pyrazolate complex [μ-Cu3((3,5-CF3)2pz)3] dissolved in CH3CN, in air. Blue crystals are produced by slow evaporation of the acetonitrile solvent. The X-ray structure of [PPN][trans-Cu6((3,5-CF3)2pz)6(OH)6(NO2)] complex shows the nitrite anion sits in the hexanuclear cavity and is perpendicular to the copper plane with a O−N−O angle of 118.3(7)°. The 19F and 1H NMR of the pyrazolate ring atoms are sensitive to the anion present in the ring. Anion exchange of the NO2 by Cl can be observed easily by 1H NMR.