Problem of a Wide Variety of Products in the Cu(hfac)₂−Nitroxide System

The stereochemically flexible Cu(hfac)2 metal−ligand system when combined with polyfunctional nitroxides leads to a variety of solids with varying structure and composition. While investigating the products of Cu(hfac)2 interaction with spin-labeled pyrazole 4,4,5,5-tetramethyl-2-(1-methyl-1H-pyrazol-4-yl)-imidazoline-3-oxide-1-oxyl, we have isolated a family of (12) heterospin compounds differing in structure and composition in the solid state. In synthetic systems, these compounds often cocrystallize and must be separated mechanically. It is also shown that minor variation of the structure of the solid heterospin complex can substantially change the magnetic properties of compounds

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]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