Ferromagnetic materials organic

Nitroxides are persistent free radicals [1] which can often be isolated and handled as kinetically stable species. Nitroxides react rapidly with carbon free-radical intermediates [2] with well-characterized rate constants [3], and can thus be used as kinetic and mechanistic probes, as well as to trap carbon radicals in synthetic processes. They are easily oxidized or reduced, and thus have a rich redox chemistry that has been utilized for a variety of oxidations. As nitroxides have an unpaired electron, they are paramagnetic and thus ESR active, making them valuable as spin labels for biomolecules [4] and as spin traps for transient radicals [5]. In addition, nitroxides have been developed as organic ferromagnetic materials [6]. The synthesis of nitroxides has been reviewed in 1994 [7]. This review will focus on the synthetic applications of nitroxides. 

Discoveries of purely-organic ferromagnetic materials, i.e., materials which do not contain transition metals or rare-earth elements, have been reported. The possibility of... 

As mentioned in the beginning of this chapter, there have been several reports that claim to have found ferromagnetism in organic polymers. Some of the results are summarized in Table 12.3, where the spin concentrations (per monomer unit) estimated from the reported saturation magnetization, using g = 2 and S =, are shown together with the transition temperatures. Some of them were prepared with moderate oxidation by iodine or oxygen, but most materials were prepared by heat treatment, pyrolysis, or explosion. 

Several attempts have been made to prepare ferromagnetic polymers. As yet, only a few papers have shown the occurrence of ferromagnetic interaction. Organic ferromagnetic polymers seem to be possible, although there are many problems still to be solved to create magnetic materials. 

Finally, synthetic metals made of polymeric organic molecules may also show the property of ferromagnetism. Organic materials of this kind were first demonstrated in 1987 by Ovchinnikov and his co-workers at the Institute of Chemical Physics in Moscow. The polymer they used was based on a polydiacetylene backbone, which contains alternating double-single and triple-single bonds between the carbon atoms of the molecule (10.2). 

This highly conjugated molecule was stabilised with nitroxyl biradical side chains. The resulting material had sufficient ferromagnetism that a usable compass needle could be made from it. Despite the success of this demonstration, organic ferromagnetism remains a curiosity. Such polymers are not likely to replace conventional ferromagnetic metals in any application within the foreseeable future. 

Donnio, B., Garcia-Vazquez, P., Gallani, J.-L., Guillon, D. and Terazzi, E. (2007) Dendronized Ferromagnetic Gold Nanopartides Self-Organized in a Thermotropic Cubic Phase. Advanced Materials, 19, 3534-3539. 

The first chemical transformations carried out with Cjq were reductions. After the pronounced electrophilicity of the fullerenes was recognized, electron transfer reactions with electropositive metals, organometallic compounds, strong organic donor molecules as well as electrochemical and photochemical reductions have been used to prepare fulleride salts respectively fulleride anions. Functionalized fulleride anions and salts have been mostly prepared by reactions with carbanions or by removing the proton from hydrofullerenes. Some of these systems, either functionalized or derived from pristine Cjq, exhibit extraordinary solid-state properties such as superconductivity and molecular ferromagnetism. Fullerides are promising candidates for nonlinear optical materials and may be used for enhanced photoluminescence material. 

As mentioned before, we shall use small molecules to introduce the fundamentals for more complex molecules, the real core of this book, which will be listed in the next section. Such molecules form solids with remarkable properties (metallicity, superconductivity, ferromagnetism, etc.), some of them at ambient conditions or at much lower hydrostatic pressures than those found for H2 and N2, and some technological applications have been already developed, deserving the name of functional materials. Most of the molecules studied in this book are planar, or nearly planar, which means that the synthesized materials reveal a strong 2D structural character, although the physical properties can be strongly ID, and because of this 2D distribution we shall study surfaces and interfaces in detail. In particular, interfaces play a crucial role in the intrinsic properties of crystalline molecular organic materials and Chapter 4 is devoted to them. 

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