2D and 3D Cu(hfac)₂ complexes with nitronyl nitroxide biradicals

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]₂L ⁴ 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 Cu ²⁺-O-^.N< and >N-^.O-Cu²⁺-O- ^.N< exchange clusters.