Conduction Mechanism of Metallic Organic Conductor with 1 : 1 Composition

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It has been widely believed that organic conductors with 1:1 composition are insulators. Nonetheless, we have found that an organic conductor (TTM-TTP)IィイD23ィエD2 exhibites metallic conductivity down to 160 K, and that the insulating state below this temperature is paramagnetic. The re-investigation of magnetic susceptibility together with the measurements of ィイD113ィエD1C-NMR and low-temperature X-ray diffraction have, however, revealed that the low temperature state is a non magnetic insulator with two-fold lattice modulation in the stacking direction. Furthermore, we have prepared two kinds of new metallic 1:1 salts, (TTM-TTP)[C(CN)ィイD23ィエD2] and (TTM-TTP)FeClィイD22ィエD2BrィイD22ィエD2. These salts have one-dimensional uniform, columns, and are metallic down to 70 K and 160 K, respectively. Five insulating 1:1 salts with AuIィイD22ィエD2, AuBrィイD22ィエD2, HgIィイD23ィエD2(TCE), FeClィイD24ィエD2(PhCl), and FeBrィイD24ィエD2(PhCl), that have dimerized columns, have been obtained as well. ESR investigation has been carried out for (DTM-TTP)(TCNQ)(TCE) and (TMET-TTP)ィイD22ィエD2(TCNQ). The former complex has a nonmagnetic insulating state below 100 K, whereas the insulating phase of the latter complex below 120 K is paramagnetic. This difference is attributed to the structures; the former complex has one-dimensional segregated stacks, and the latter has a two-dimansional θ-type donor arrangement, in which TCNQ works as an isolated anion. These investigations indicate that the origin of the insulating state in the 1:1 organic conductors are not correlation, but one-dimensional instability such as CDW formation.