Structural and electronic properties of the one-dimensional organic metal bis(thiodimethylene)-tetrathiafulvalene tetracyanoquinodimethane

The synthesis and structural characterization at room temperature and 130 K of the organic charge-transfer salt bis(thiodimethylene)-tetrathiafulvalene tetracyanoquinodimethane (BTDMTTF-TNCQ) is reported. X-ray diffuse scattering as well as ir and Raman measurements show that the charge transfer in this salt is ∼0.5. BTDMTTF-TCNQ remains metallic down to very low temperatures but exhibits an anomaly at 175 K in the conductivity and thermopower which could be related to some unusual structural modification of the unit cell. Band-structure calculations show that this salt is a narrow-band one-dimensional metal. The high value of the spin susceptibility, the low value of the conductivity, and the observation of a 4 k F charge-density-wave (CDW) instability around room temperature prove that it is a highly correlated metal. In contrast with other salts of the TTF-TCNQ family, BTDMTTF-TCNQ does not exhibit critical 2 k F structural fluctuations. It is proposed that the absence of the 2 k F CDW transition is due to the stronger interlocking of the donor and acceptor molecules due to the presence of the sulfur atoms in the central position of the outer five-membered rings of the BTDMTTF donor