Organic magnet

Electric conductivity of ion-radical salts arises from the mobility of their unpaired electrons. At the same time, each of the unpaired electrons possesses a magnetic moment. This small magnetic moment is associated with the electron quantum-mechanical spin. Spin-originated magnetism as a phenomenon is described in many sources (see, e.g., monographs by Khan 1993, Bauld 1997, Itokh and Kinoshita 2001 and reviews by Miller 2000, Miller and Epstein 1994, 1995, Wudl and Thompson 1992). This section is, naturally, devoted to the organic magnets based on ion-radicals. 

Any salt formed from two ion-radicals has two unpaired electrons one belongs to the cation-radical and the other to the anion-radical. If the spins of these two electrons have an antiparallel orientation, the corresponding magnetic moments are compensating. If both spins are in parallel orientation, their magnetic moments are added together. 

The problem of the ferromagnetism of a solid ion-radical salt has two important points. One is ferromagnetism at the level of a salt as the molecule, which consists of two paramagnetic species. Another is ferromagnetism at the level of a solid sample formed from assemblies of the spin-bearing molecules. These molecules may contain one or more magnetic centers. 

Assemblies of molecules are most often found in molecular crystals with very weak interactions between the molecular entities. They can also be found in extended systems, built from molecular or ion-radical precursors, in a way that maximizes the interactions between the precursors and, hopefully, yields bulk magnetic properties. 

Replacing (FeCp j) with nonspin (CoCp 2) in the salt with (TCNE) eliminates magnetic coupling. This demonstrates that both cation and anion of these salts need to have unpaired electrons to stabilize ferromagnetic coupling. In other words, spin sites on both the cation-radical and anion-radical parts of the salt contribute to the material s magnetic properties. 

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Organic Magnetic Resonance (now Magn Reson Chem ) Progress in Nuclear Magnetic Resonance Spectroscopy Spectrochimica Acta Part A Molecular Spectroscopy Spectroscopy Letters Spectroscopy An International Journal... 

After reviewing the nature of organic ion-radicals and their ground-state electronic structure, the book discusses their formation, the relationship between electronic structure and reactivity, mechanism and regulation of reactions, stereochemical aspects, synthetic opportunities, and practical applications. Additional topics include electronic and optoelectronic devices, organic magnets and conductors, lubricants, other materials, and reactions of industrial or biomedical importance. 

Aryl nitrenes have been studied extensively over the last decades and are used in several industrial processes such as microlithography. Aryl nitrenes have also been used in photoaffinity labeling bioorganic molecules. The pursuit for organic magnetic material has sparked renewed interested in nitrene intermediates, which are ideal candidates for magnetic material because of their high spin properties. ... 

Palacio F, Antorrena G, Castro M, Burriel R, Rawson J, Smith JNB, Bricklebank N, Novoa J, Ritter C (1997) High-temperature magnetic ordering in a new organic magnet. Phys Rev Lett 79 2336-2339... 

Rajca and co-workers have studied star-branched and dendritic high-spin polyradicals which are potential organic magnets. Representative data were obtained for the model tetra-anionic compound 55. Three redox waves were observed by cyclic voltammetry and differential pulse voltammetry for a four-electron process between the potentials of -2.00 and -1.20 V (vs. SCE). Electrochemical experiments with these materials have usually been performed at 200 K. The polyradicals, which are less stable for systems with more unpaired electrons, have been characterized by spectroscopic studies, ESR data, and SQUID magnetometiy. 

Interest in the preparation of high-spin organic compounds has led to the matrix isolation of polynitrenes, such as 57-61. " These species have been studied primarily by EPR spectroscopy, but increasing use is being made of matrix IR and UV-vis spectroscopy. Density functional theoretical calculations have been used to assign the vibrational spectra that have been observed. Polynitrenes are under active smdy by material scientists interested in the development of organic magnets. 

Permission to use published material was granted by Finnigan MAT, American Society of Mass Spectrometry, John Wiley and Sons, Inc., Journal of Chemical Education, and Organic Magnetic Resonance. Processing software was furnished by Herbert Thiele (Bruker Instrument Corp.). 

Organic Magnetic Resonance (now Magn Reson Chem )... 

Fig. 3.63 First order splitting patterns for aromatic protons. Data reproduced from M. Zanger (1972). The Determination of Aromatic Substitution Patterns by Nuclear Magnetic Resonance , Organic Magnetic Resonance, 4,4. Published by Heyden and Son Ltd.

Fig. 3.69 60 MHz proton magnetic resonance spectra of methyl isobutyl ketone (10.6 mg, 1.1 x 10 4mol) in CC14 (0.5 ml) containing various amounts of Eu(pfd)3 A, 0.0 mg B, 13.5 mg C, 21.1 mg D, 29.0 mg. Data reproduced from H. E. Francis and W. F. Wagner (1972). Induced Chemical Shifts in Organic Molecules Intermediate Shift Reagents , Organic Magnetic Resonance, 4,190 (Fig. 1), Heyden and Son Ltd.

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