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Issue 7, 2013
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A self-assembled Cu(II)4 [2 × 2] grid with organic radicals

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A novel multitopic, two-pocket ligand HLnitnitnitnit, containing the nitronyl nitroxide radical, has been designed for a self-assembled [2 × 2] grid system. HLnitnitnitnit is not stable in methanol and slowly undergoes a disproportionation, during which the nitronyl nitroxide radical converts to the diamagnetic amidino oxide. In situ reaction of HLnitnitnitnit with Cu(BF4)2 in methanol depending on the reaction time affords self-assembled [2 × 2] grids (Lnitnitnitnit)2(L)2Cu(II)4(BF4)4·CH3OH (1) or (Lnitnitnitnit)0.5(L)3.5Cu(II)4(BF4)4·CH3OH (2), in which L contains an amidino oxide arising from a 3-electron reduction of the nitronyl nitroxide radical. The percentages of stable radical in grids 1 and 2 as determined by X-ray are 50 and 12.5%, respectively. Structures 1 and 2 contain a six-coordinated distorted Cu(II) that is oxo-bridged at 140°. The nitronyl nitroxide radical coordinates via the oxo-atom of the N+–O fragment in a chelating fashion and lies in the equatorial plane of the metal ion. The magnetic properties of 1 could be fitted to a 5-spin Hamiltonian with JCu–Cu = +3.1 cm−1 and JCu–Nit = −278 cm−1, while those of 2 to a 4-spin Hamiltonian with JCu–Cu = +2.9 cm−1. The Q-band EPR spectra of 1 and 2 recorded in solution at 20 K showed intricate anisotropic features of the Cu(II) ion and a much weaker signal of the –NO˙ fragment, associated with a strong Cu(II)–Nit antiferromagentic coupling. The DFT calculated (B3LYP/TZVP/6-31G*) magnetic coupling constants for the grid of 1 were JCu–Cu = +5 cm−1 and JCu–Nit = −282 cm−1, which are in very good agreement with the experimentally obtained values.

Graphical abstract: A self-assembled Cu(ii)4 [2 × 2] grid with organic radicals

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Publication details

The article was received on 25 Aug 2012, accepted on 10 Sep 2012 and first published on 11 Sep 2012

Article type: Paper
DOI: 10.1039/C2DT31946B
Citation: Dalton Trans., 2013,42, 2371-2381
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    A self-assembled Cu(II)4 [2 × 2] grid with organic radicals

    K. V. Shuvaev, S. Sproules, J. Mikko. Rautiainen, E. J. L. McInnes, D. Collison, C. E. Anson and A. K. Powell, Dalton Trans., 2013, 42, 2371
    DOI: 10.1039/C2DT31946B

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