Metal–Insulator Transition of the New One-Dimensional Organic Conductors with Complete Uniform Stacks: (DMEDO-TTF)2X(X= ClO4and BF4)

Abstract

The structural, transport, and magnetic properties of the new organic conductors (DMEDO-TTF)2X (X = ClO4 and BF4), where DMEDO-TTF is dimethyl(ethylenedioxy)tetrathiafulvalene, have been investigated. These compounds have a complete uniform stack structure, indicating that a quasi-one-dimensional 3/4-filled band without a dimerization gap is realized. The ClO4 and BF4 salts show a first-order metal–insulator (MI) transition at approximately 190 and 210 K, respectively, in the cooling process. The ground state is a nonmagnetic insulator on the basis of magnetic susceptibility measurements. Low-temperature X-ray diffraction measurements show that the MI transition originates in the anion ordering transition with a superstructure wave vector of \(\boldsymbol{{q}} = (0,1/2,0)\) corresponding to the stacking direction; the uniform donor stacking structure changes to the tetramerized structure with a large shift of the donors. The shift of the anion toward the central two donors in a tetramer indicates that the...