Spin-ladder systems

Radicals have been known for many years to form organic paramagnetic materials with numerous magnetic properties (ferro- or ferri-magnetism, spin Peierls transition, spin frustration, spin ladder systems) (see [51-60] for verdazyl radicals, [61-68] for thiazyl radicals, [69] for nitronyl nitroxide and [70-78] for Tempo radicals) (Fig. 6). When they are in their cationic form, they are valuable candidates for an association with the M(dmit)2 systems they will then provide the magnetic properties thanks to their free electron(s), whereas the M(dmit)2 moieties will provide the electrical properties. 

This section is devoted to four main topics spin-Peierls systems, spin-ladder systems, systems exhibiting ferromagnetic interaction, and bulk ferromagnets. To our knowledge, no dithiolene-based films (including LB films) have been studied for their ferromagnetic properties and no patent has claimed the use of these materials in this area. 

The related (p-EPYNN)[Au(dmit)2] complex has also been synthesized. However, its crystal structure does not correspond to a true spin-ladder system but rather to ID chains of [Au(dmit)2 alternating with ID chains of (p-EPYNN)+ still presenting ferromagnetic interactions at low temperature (304). 

Like the dmit complexes, the mnt complexes are also promising candidates for the synthesis of spin-ladder systems. As previously discussed (Section II.B.l.b), metal-like D-A conductors have been obtained when associating M(mnt)2 and Per (159). Spin-ladder D-A systems have been obtained when associating M(mnt)2 and the dithiopheno-tetrathiafulvalene (DT-TTF = C10H4S6) donor (Scheme 15). 

Although isostructural to the Au complex, the Ni and Pt salts do not form spin-ladder systems. This may be due to slight differences in the transfer integrals within the DT-TTF stacks and also to the paramagnetism of [M(mnt)2] (M = Ni, Pt) that may interact with the DT-TTF system. Related Co and Fe compounds have also been reported (311), but they are just simple ionic salts as shown by their 1 1 stoichiometry (instead of the 2 1 stoichiometry for the Au, Ni and Pt compounds). Very recently, Ribera et al. (307) published an excellent and detailed report on this family of compounds. 

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