2D and 3D Cu(hfac)₂ Complexes with Nitronyl Nitroxide Biradicals

Abstract

Reactions between Cu(hfac)2 and nitronyl nitroxide biradicals 1,4-bis[4-(4,4,5,5-tetramethyl-3-oxide-1-oxyl-4,5-dihydro-1H-imidazol-2-yl)pyrazol-1-yl]butane (L4) and 1,8-bis[4-(4,4,5,5-tetramethyl-3-oxide-1-oxyl-4,5-dihydro-1H-imidazol-2-yl)pyrazol-1-yl]octane (L8) gave respectively a framework compound [Cu(hfac)2]2L4 and a layered polymer compound [Cu(hfac)2]2L8. The framework of [Cu(hfac)2]2L4 consists of 66-membered condensed metallocycles. Inside the framework, the structure has macrohelixes (pitch ∼25 Å) extending along the [001] crystallographic direction. All the helixes have the same direction of winding; the crystals, therefore, are optically active, the structure corresponding either to P-isomer (P41212) or to M-isomer (P43212). The long distances between the Cu atoms and the O atoms of the coordinated >N−O groups (Cu−O 2.351−2.467 Å) are responsible for ferromagnetic exchange interactions in Cu2+−O−NN−O−Cu2+−O−N< exchange clusters