BEDO-TTF

Scheme 7 Chemical stractures of HMTTeF, BEDO-TTF(BO) and EOET...

Horiuchi S, Yamochi H, Saito G, Jeszka JK, Tracz A, Sroczynska A, Ulanski J (1997) Highly-oriented BEDO-TTF molecules in metallic polymer composites. Mol Cryst Liq Cryst 296 365-382... 

Yamochi H, Kawasaki T, Nagata Y, Maesato M, Saito G (2002) BEDO-TTF complexes with magnetic counter ions. Mol Cryst Liq Cryst 376 113-120... 

TRANSPORT, MAGNETIC AND OPTICAL PROPERTIES OF A QUASI-TWO-DIMENSIONAL ORGANIC METAL BASED ON BEDO-TTF (BIS-(ETHYLENEDIOXY)TETRATHIAFULVALENE)... 

The aim of this article is to show that the new quasi-two-dimensional organic conductor p -(BEDO-TTF)5[CsHg(SCN)4]2 [hereafter called (BEDO)CsHg] (BEDO-TTF - bis-(ethylenedioxy)tetrathiafulvalene) which contains closed and open orbits displays rather complicated oscillatory spectra associated with magnetic breakdown (MB) and quantum interference (QI) effects. Tight binding band structure calculations for this compound are proposed to characterise its Fermi surface. The aim of the article includes also an investigation of the optical conductivity anisotropy with polarized infrared reflectance spectra. 

The crystal structure of (BEDO-TTF)5[CsHg(SCN)4]2 is built from BEDO-TTF layers which alternate along the c-direction with inorganic layers wherein Cs+ cations and [Hg(SCN)4]2" anions form an extended two-dimensional network [7]. 

Figure 1. Donor layers of (BEDO-TTF)5 [CsHg(SCN)4]2 where the different types of chains and donor... donor interactions have been labelled.

This structure differs from those of a-(BEDT-TTF)2MHg(SCN)4 salts with respect to both the donor and acceptor sublattices [7]. The donor layers in the present salt have a P -type arrangement (Fig. 1) and are built from three different BEDO-TTF donors (A, B and C). There are three different types of intermolecular interactions with the slab of organic molecules, the relative orientation of which allows us to describe this layer as being composed of a series of parallel stacks of slipped donors along the (2a-b)-direction, as a series of step-chains along the a+2b) -direction, or as a series of parallel... 

Some weak features attributed to the BEDO-TTF intramolecular vibrations are observed below 1600 cm-1 and a narrow double band near 2100 cm 1 is assigned to the CN stretching vibration of the anion. Below 200 K the qualitative change in the reflectivity spectra for E L is accompanied by the appearance of new vibrational features at 862 and 1012 cm 1. 

Figure 2.. Polarized reflectivity spectra of p-BEDO-TTF)5[CsHg(SCN)4]2 for E 1 L and E L at 300, 200, 100 and 10 K. (L is BEDO-TTF stack direction). The fit with Drude-Lorenz model for T=10 K is shown by thin solid line.

Based on the structure of the donor layers (Fig. 1) of (BEDO-TTF)CsHg, the band structure for these layers was calculated near the Fermi level (Fig.4). As shown in Fig. 1, there are five donors per repeat unit of the layer so that the five bands of Fig. 4 are... 

Figure 4. Calculated dispersion relations of the HOMO bands in (BEDO-TTF)5[CsHg(SCN)4]2...

Figure 6. FFT spectrum for Shubnikov-de Haas oscillations (inset) for (BEDO-TTF)5[ScHg(SCN)4]2 at T=1.55K and the field direction parallel to the c -axes (0=0°). Four different frequencies Fi 650T, F2 2600T F3 3200T and F4 3850T are clearly seen.

The behaviour of the polarized reflectivity and optical conductivity spectra of new quasi-two-dimensional organic conductor p -(BEDO-TTF)5[CsHg(SCN)4]2 versus temperature for E L and E1. L are quite different. For E . L, the temperature changes of R(ro) and ct(co) are due to the decrease of the optical relaxation constant of the free carriers as expected for a metal. For E L at temperatures below 200 K, the energy gaps in the ct(co) spectra at about 4000 cm 1 and at frequencies below 700 cm 1 appear simultaneously with the two new bands of ag vibrations of the BEDO-TTF molecule activated by EMV coupling. This suggests a dimerization of the BEDO-TTF molecules in the stacks, which leads to a metal-semiconductor transition.. In the direction perpendicular to L, the studied salt shows metallic properties due to a very favourable overlap of the BEDO-TTF molecular orbitals. 

The behaviour of the quantum oscillations in (BEDO-TTF)5[CsHg(SCN)4]2 seems to be in good agreement with the predictions of tight binding band structure calculations. The additional frequencies in the SdH oscillations spectrum are most probably caused by the quantum interference effect. Thus, we propose that Fig. 5 provides an adequate description of the Fermi surface of (BEDO-TTF)5[CsHg(SCN)4]2 and that the... 

The synthesis of bis(ethylenedioxy)tetrathiafulvalene (BEDO-TTF or BO) represented a formidable synthetic challenge its preparation was... 

Recently, Heiberg et al. [26] have studied polarizabilities of the intermolecular contacts in bis(ethylenedithiolo)tetrathiafulvalene (BEDT-TTF) and bis(ethylenedioxy)tetrathiafulvalene (BEDO-TTF) molecular crystals by polarizing microscope techniques. The principal refractive indices and the corresponding optical axes have been calculated by tensorial addition of the bond polarizabilities of all bonds in the molecules. Comparison of calculated and measured values of the relative polarizabilities showed that the polarizabilities of the molecules only cannot yield the measured indicatrix and axes angle. Thus polarizabilities with other orientations must be involved. From the crystal structure of the molecular crystals it is known that 10 and four different contacts exist between the molecules of BEDT-TTF and BEDO-TTF, respectively, with contact distances lower than van der Waals distances. Assigning of polarizabilities of these contacts can explain the measured behavior. 

A large variety of other 2D superconducting salts with different organic constituents have been synthesized. Building blocks are for example DMET, MDT-TTF, BEDO-TTF or also the acceptor molecule M(dmit)2 with M = Ni, Pd, or Pt. These latter salts, however, will not be discussed in general, but rather when measurements of their FS will be presented. 

SdH measurements unraveled both the band structure of (BEDO-TTF)2-Re04(H20) and resolved the question of a DW transition in the ambi-... 

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