Electrons in Specific Molecular Systems
Organic molecular systems are diamagnetic  except for specific molecular systems composed of organic radicals and related species . Spin alignments and spin-mediated properties of these unusual systems are examined here theoretically First, orbital symmetry rules for effective exchange interactions between organic radicals are derived on the basis of intermolecular interaction theories. Second, the reliability and utility of first-principle calculations are discussed in relation to the theoretical prediction of the sign and magnitude of effective exchange integrals (J ab ) between nitroxide molecules, which have been used as stable building blocks for organic ferromagnets. Third, the ferromagnetic phase transition in the case of the β-phase of para-nitrophenyl nitronyl nitroxide (p-NPNN)  is examined as a typical example that illuminates the crystal structure-ferromagnetism relationship. Last, possible molecular systems with both conduction and localized electrons are discussed from the standpoint of new specific molecular functional materials such as organic ferromagnetic metals and spin-mediated organic superconductors . The formal relationship between molecular magnetism and molecular recognition with hydrogen bonding is also pointed out based on the effective spin Hamiltonian models.
KeywordsEffective Exchange Heisenberg Model Ferromagnetic Interaction Hole Doping Spin Population
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