Supramolecular Architectures and Magnetic Interactions in Crystalline α-Nitronyl Nitroxide Radicals

Abstract

The design of purely organic magnetic materials has been the goal of many research groups during the last decade [1]. As result of a systematic synthetic effort, it has been possible to obtain different kinds of crystalline organic free radicals that show relevant magnetic properties and, in very exceptional cases, even bulk ferromagnetism [2]. The number of these compounds is now large enough to make it possible to look at the general trends of the structure-magnetism relationship, even in a statistical form. That is, one can look at the connections between the crystal packing of a material and its magnetic properties. Understanding the driving forces behind already known compounds will be very useful for the design of new purely organic magnetic materials in which the magnetic properties are enhanced. Because the packing of a given molecular system can be strongly influenced by the functional groups present in the molecule, we have to look at data in families of compounds. We have chosen to focus our analysis on just one uniform family of magnetic compounds, that of the so called α-nitronyl nitroxide (or α-nitronyl aminoxyl) radicals [3], whose general formula is shown in Figure 1 and which characterized by the presence of a five-membered ring with two nitronyl groups attached in an alpha position to a C(sp2) carbon.