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

Shuvaev, K. V., Sproules, S. , Rautiainen, J. M., McInnes, E. J. L., Collison, D., Anson, C. E. and Powell, A. K. (2013) A self-assembled Cu(II)4 [2×2] grid with organic radicals. Dalton Transactions, 42(7), pp. 2371-2381. (doi: 10.1039/C2DT31946B)

Abstract

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 methanoland 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 methanoldepending 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 whichL 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 1could 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 2recorded 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 of1 were JCu–Cu = +5 cm−1 and JCu–Nit = −282 cm−1, which are in very good agreement with the experimentally obtained values.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Sproules, Dr Stephen
• Authors: Shuvaev, K. V., Sproules, S., Rautiainen, J. M., McInnes, E. J. L., Collison, D., Anson, C. E., and Powell, A. K.
• College/School: College of Science and Engineering > School of Chemistry
• Journal Name: Dalton Transactions
• Publisher: Royal Society of Chemistry
• ISSN: 1477-9226
• ISSN (Online): 1477-9234