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Infrared and Raman spectra of 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene (BDT-TTP) and 1,3,4,6-tetrathiapentalene-2,5-dione (TTP-DO) are reported. The vibrational modes of TTP-DO are assigned with the aid of the depolarization ratio of solution Raman spectra, polarized reflection spectra and polarized Raman spectra. A D2h symmetry is assumed for the BDT-TTP molecule and its in-plane fundamental vibrations are assigned with the aid of the polarization ratio and the correlation with TTP-DO, tetrathiafulvalene (TTF), tetramethyltetrathiafulvalene (TMTTF) and bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF). Normal coordinate calculation with a modified internal valence force field was carried out for the in-plane fundamental vibrations of TTP-DO and BDT-TTP. Ab initio calculations of the normal modes of BDT-TTP0 and BDT-TTP+ are compared with the empirical analysis.

θ-(BDT-TTP) 2 Cu(NCS) 2 (BDT-TTP=2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathia-pentalene) is a highly correlated organic conductor with a quasi-two-dimensional electronic structure. This compound undergoes a second-order phase transition at 250 K. Below the phase transition temperature, the optical gap significantly broadens. From the analysis of the Raman spectrum, we found that the phase transition was accompanied by a disproportionation of charge. The separated charge forms a vertical stripe along the b-axis, and the b-axis is likely to be doubled at 5 K.

We have obtained a new molecular metal containing a rare-earth complex anion, g "-(BO) 2 [YbCl 4 (H 2 O) 2 ]. This salt retains metallic conductivity down to 4 K. This crystal is metastable at room temperature; it gradually tranforms into another phase, f -(BO) 2 [YbCl 4 (H 2 O) x ], which becomes insulating below 210 K. The g "-phase crystal have a chain structure of the anions, formed by OH···Cl hydrogen bonding. This is the first example of a ~ molecular conductor based on an assembled rare-earth complex. Preparation, structure and resistivity of (BO) 2 [YbCl 4 (H 2 O) x ] system is reported. Rare-earth molecular conductors structure f -electrons

Four kinds of (1:1) and (1:2) salts of 3-(4- and 3-ethyl-pyridinium)-1,5-diphenylverdazyl radical cations with tetracyanoquinodimethanide (TCNQ) anion ([p-EtPyDV]+[TCNQ]− (1), [m-EtPyDV]+[TCNQ]− (2), [p-EtPyDV]+[TCNQ]2− (3), and [m-EtPyDV]+[TCNQ]2− (4)) have been prepared, and the magnetic susceptibilities (χM) measured between 1.8 and 300 K. The values of χMT at 300 K are 0.437, 0.383, 0.620, and 0.482 K emu mol−1 for the salts (1), (2), (3), and (4), respectively, and decrease by lowering the temperature. The χM of the salt (2) follows the Curie–Weiss law with a Curie constant of 0.374 K emu mol−1 and a negative Weiss constant of −2.4±0.2 K in the temperature region 1.8–300 K, indicating disappearance of a net magnetic moment due to the formation of strong spin pairs in TCNQ anion molecules. The χM of the salt (3) shows a broad maximum at T max = 118 ± 2 K and can be well explained by a singlet–triplet equilibrium model with 2 J / k B = - 190 K The χM of the salt (4) shows a broad maximum at T max = 9.3 ± 0.5 K The χM can be well reproduced by the sum of the contributions from: (i) a one-dimensional (1D) Heisenberg antiferromagnetic alternating-chain system with 2 J / k B = - 15.2 K (alternation parameter α=J2/J1=0.4); and (ii) the dimer system with 2 J / k B = - 741 K The magnetic property of (4) was discussed based on the results obtained by crystal structure analysis of (4). On the other hand, the susceptibility of the salt (1) showed anomalous magnetic behavior that cannot be explained by a simple model. The (1:1) salts (1) and (2) are insulators. On the other hand, the pressed pellet conductivity (σ) of the (1:2) salts (3) and (4) at 20°C was σ=6.9×10−2 and 1.5×10−3 S cm−1 with activation energy EA=0.072 and 0.25 eV, respectively, showing the property as semiconductor. The two (1:2) salts (3) and (4) are new, genuine organic magnetic semiconductors.

The electron–molecular vibration (EMV) coupling constants and the accompanying vibronic energy values of five kinds of organic donor molecules (TTF +1 , TTP +1 , TTPY +1 , TOF +1 and TSF +1 ) are crucial ingredients of metallic organic salts, and have been theoretically estimated in order to systematically investigate their dependencies on the molecular structures. The effect of the replacement of sulfur atoms in TTF +1 with oxygen and selenium atoms (TOF +1 and TSF +1 ) has been paid particular attention. It has been found that the EMV coupling constant decreases in the order of TOF +1 >TTF +1 >TSF +1 >TTP +1 >TTPY +1 . That is, the smaller coupling constants appear in the larger-sized molecule with heavier atoms.

A new charge transfer complex (CPDT-STF)(TCNQ) has been prepared. An X-ray crystal structure analysis revealed that this complex is composed of the donor and acceptor sheets orthogonally arranged to each other, which is similar to (ET)(TCNQ) and (ET)(TCNQF 1 ). The band calculations indicate that the CPDT-STF layer has a significantly two-dimensional interaction, while the TCNQ one has a one-dimensional Fermi surface. The electrical resistivity of the present complex showed metallic temperature dependence down to 0.6 K. The thermoelectric power was negative and changed from the positive to the negative gradient at 60 K. The static magnetic susceptibility and transport properties indicate coexistence of local and itinerant electrons in the present complex.

A new ST-TTP donor TMEO-ST-TTP, where TMEO-ST-TTP is 2-[4,5-bis(methylthio)-1,3-diselenol-2-ylidene)-5-(4,5-ethylendioxy-1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene, has been prepared. It affords highly conducting PF 6 - and AsF 6 salts retaining metallic conductivity down to 4.2 K, while the TCNQ complex and ClO 4 - salt are low conductive semiconductors. X-Ray structure analyses reveal that (TMEO-ST-TTP)(TCNQ)(PhCl) has a DA type mixed stack, and that the donor array of (TMEO-ST-TTP) 2 ClO 4 (DCE) in the conducting sheet resembles β-BEDT-TTF salts.

Polarized reflectance spectra were measured on the conductive (010) plane of metallic (BDT-TTP) 2 X (X=SbF 6 , AsF 6 ) single crystals at room and low temperatures. Well-defined plasma edges appeared in both directions parallel (// a ) and perpendicular (⊥ a ) to the molecular stack, indicating two-dimensional band structures with a significant anisotropy. The intra- and inter-stack transfer integrals were estimated from the plasma frequencies in the framework of tight-binding model. Based on these transfer integrals, the energy dispersion, density of state, and Fermi surface were calculated. The Fermi surfaces of both compounds were open in the k c direction. The temperature dependence of the transfer integrals was determined by analyzing the low-temperature spectra. The intra-stack transfer integral increased by about 30% whereas the enhancement of inter-stack transfer integral was very weak. So the system became more anisotropic at low temperatures. The strongly appeared CH stretching mode in the ⊥ a s...

The title 1:1 composition organic conductor, with a highly one-dimensional half-filled energy band, exhibits metallic conductivity down to ${T}_{\mathrm{MI}}\ensuremath{\approx}160\mathrm{K}$, but the spin susceptibility follows the one-dimensional Heisenberg model from room temperature to 2 K, without any anomaly at ${T}_{\mathrm{MI}}$. The insulating state is regarded as a Mott insulator. The small $U$, related to the extended molecular structure, gives rise to the small charge gap and the high-temperature metallic conduction.

Tris-fused tetrathiafulvalenes, TTC n -TTPY (n = 2-5) have been prepared, and the structural and conducting properties have been investigated. The neutral crystals of TTC n -TTPY exhibit low electrical resistivity as a neutral organics; the lowest is 80 Ωcm in TTC2-TTPY. When TTC n -TTPY is exposed to iodine vapor, the sample becomes highly conducting in a few minutes, but again becomes insulating on account of overdoping. When taken out from the iodine atmosphere, the high conducting state is recovered, and the high conducting sample shows metallic conductivity and thermoelectric power down to helium temperatures.

θ-(BDT-TTP) 2 Cu(NCS) 2 (BDT-TTP=2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathia-pentalene) is a highly correlated organic conductor with a quasi-two-dimensional electronic structure. This compound undergoes a second-order phase transition at 250 K, which accompanies a disproportionation of charge. The optical spectrum and magnetic susceptibility suggest that the separated charge forms a vertical stripe along the b -axis. The ESR experiment shows that the ground state is a non-magnetic state, which suggests the doubling of b -axis below 5 K. The properties which characterize the CO and magnetic phase transition were compared with those of θ-(BEDT-TTF) 2 RbZn(SCN) 4 .

The metal-insulator phase transition accompanying charge disproportionation was studied for two charge-transfer salts, θ-(BDT-TTP) 2 Cυ(NCS) 2 and (TTM-TTP)I 3 . In the former compound, the localized generates a charge disproportionation such as (+0.1, +0.9). On the other hand, the charge disproportionation was not found in (TTM-TTP)I 3 . Alternatively, the intra-molecular charge distribution becomes asymmetric below the phase transition temperature Both phenomena are derived from the localization of charge with a symmetry breaking.

New TTF derivatives, bis(2-methylidene-1,3-dithiol[4,5- d ])tetrathiafulvalenes (BDT-TTF's, 1 ), and their unsymmetrical derivatives, (2-methylidene-1,3-dithiolo[4,5- d ])tetrathiafulvalenes (MeDT-TTF's, 2 , CpDT-TTF's, 3 ) which are condensed with one or two 1,3-dithiol-2-ylidene moieties, were synthesized. The electrochemical properties of these donors were investigated by means of cyclic voltammetry. The X-ray structure of dimethylthio derivative of CpDT-TTF showed that the molecule is almost planar except for cyclopentane ring and there were shorter S…S contacts than the sum of van der Waals radii. BDT-TTF's formed charge-transfer complexes with TCNQF 4 whose electrical conductivities were 10 −3 −10 −4 Scm −1 . On the other hand, DT-TTF's afforded several metallic cation radical salts, in particular, I 3 and ClO 4 salts of ethylenedithio-MeDT-TTF exhibited metallic behavior down to 0.5 K.

We present the polarized Raman spectra and magnetic susceptibility of $\ensuremath{\theta}\ensuremath{-}(\mathrm{B}\mathrm{D}\mathrm{T}\ensuremath{-}\mathrm{T}\mathrm{T}\mathrm{P}{)}_{2}\mathrm{Cu}(\mathrm{NCS}{)}_{2}$ which undergoes a charge-ordering phase transition at ${T}_{\mathrm{CO}}\ensuremath{\sim}250\mathrm{K}.$ From the splitting of the ${\ensuremath{\nu}}_{2}$ band, the charge-disproportionation ratio \ensuremath{\delta} is estimated as 0.4 at \ensuremath{\sim}10 K. The linewidth of ${\ensuremath{\nu}}_{2}$ suggests the fluctuation in charge distribution above ${T}_{\mathrm{CO}}.$ The magnetic susceptibility of $30\mathrm{K}lTl300\mathrm{K}$ follows the Curie--Weiss Law with the Curie constant of 0.154 emuK/mol and Weiss temperature of -29 K. The single-crystal ESR experiment shows a magnetic phase transition to a spin-singlet state at 5 K. The polarized Raman spectra and magnetic property suggest the view that the positive charge is vertically ordered along the b-axis.

Five kinds of (1:1), (1:3), and (2:1) salts of 3-[4-(diethylmethylammonio)phenyl]-1,5-diphenyl-6-oxoverdazyl radical cation [V](+) with M(dmit)(2) anions (M = Ni, Zn, Pd, and Pt, dmit = 1,3-dithiol-2-thione-4,5-dithiolate) ([V](+)[Ni(dmit)(2)](-) (1), [V](+)[Ni(dmit)(2)](3)(-) (2), [V](+)(2)[Zn(dmit)(2)](2-) (3), [V](+)(2)[Pd(dmit)(2)](2-) (4), and [V](+)(2)[Pt(dmit)(2)](2-) (5)) and an iodide salt of [V](+) ([V](+)[I](-) (6)) have been prepared, and the magnetic susceptibilities (chi(M) values) have been measured between 1.8 and 300 K. The chi(M) of the (1:1) Ni salt (1) can be well reproduced by the sum of the contributions from (i) a Curie-Weiss system with a Curie constant (C) of 0.376 K emu/mol and a negative Weiss constant (theta) of -1.5 K and (ii) the one-dimensional Heisenberg antiferromagnetic alternating chain system with 2J(A-B)/k(B) = -274 K (alternation parameter alpha = J(A-C)/J(A-B) = 0.2). The chi(M) of the (1:3) Ni salt (2) can be well explained by the two-term contributions from (i) the Curie-Weiss system with C = 0.376 K emu/mol and theta = -5.0 K and (ii) the dimer system with 2J/k(B) = -258 K. The magnetic properties of 1 and 2 were discussed based on the results obtained by crystal structure analysis and ESR measurements of 1 and 2. The chi(M) values of the (2:1) Zn, Pd, Pt salts 3, 4, and 5 and [V](+)[I](-) salt 6 follow the Curie-Weiss law with C = 0.723, 0.713, 0.712, and 0.342 K emu/mol and theta = -2.8, -3.1, -2.6, and +0.02 K, respectively, indicating that only the spins of the verdazyl radical cation contribute to the magnetic property of these salts. The salts 1, 3, and 5 are insulators. On the other hand, the conductivity (sigma) of the Ni salt 2 and Pd salt 4 at 20 degrees C was sigma = 8.9 x 10(-2) and 1.3 x 10(-4) S cm(-)(1) with an activation energy E(A) = 0.11 and 0.40 eV, respectively. The salts 2 and 4 are new molecular magnetic semiconductors.

We present spectroscopic evidence for the charge disproportionation in the crystal $\ensuremath{\theta}\ensuremath{-}{(\mathrm{B}\mathrm{D}\mathrm{T}\ensuremath{-}\mathrm{T}\mathrm{T}\mathrm{P})}_{2}{\mathrm{Cu}(\mathrm{NCS})}_{2}$ $(\mathrm{B}\mathrm{D}\mathrm{T}\ensuremath{-}\mathrm{T}\mathrm{T}\mathrm{P}=2,5\ensuremath{-}\mathrm{b}\mathrm{i}\mathrm{s}{(1}^{\ensuremath{'}}{,3}^{\ensuremath{'}}\ensuremath{-}\mathrm{dithiol}{\ensuremath{-}2}^{\ensuremath{'}}\ensuremath{-}\mathrm{ylidene})\ensuremath{-}1,3,4,6\ensuremath{-}\mathrm{t}\mathrm{e}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{t}\mathrm{h}\mathrm{i}\mathrm{a}\ensuremath{-}\mathrm{p}\mathrm{e}\mathrm{n}\mathrm{t}\mathrm{a}\mathrm{l}\mathrm{e}\mathrm{n}\mathrm{e}).$ $\ensuremath{\theta}\ensuremath{-}{(\mathrm{B}\mathrm{D}\mathrm{T}\ensuremath{-}\mathrm{T}\mathrm{T}\mathrm{P})}_{2}{\mathrm{Cu}(\mathrm{NCS})}_{2}$ is a highly correlated organic conductor with a quasi-two-dimensional electronic structure. In the electrical resistance of this compound, we found a second-order phase transition at 250 K. Below this phase-transition temperature, the optical absorption in the midinfrared region exhibits a high-frequency shift, and the Raman-active $\mathrm{C}\mathrm{=}\mathrm{C}$ stretching modes ${\ensuremath{\nu}}_{2},$ ${\ensuremath{\nu}}_{3},$ and ${\ensuremath{\nu}}_{4},$ which are sensitive to the charge on BDT-TTP, split into 12 bands at 5 K. Based on the excitation-light dependence of the Raman spectrum, we propose that a disproportionation of charge occurs below the phase-transition temperature.

Properties of metallic TTM-TTP (2,5-bis[4,5-bis(methylthio)-1,3-dithiol-2-ylidene]-1,3,4,6-tetrathiapentalene) salts with 1:1 composition, in particular magnetic properties of (TTM-TTP)[C(CN) 3 ], are reported. The results are discussed on the basis of molecular orbital calculations of on-site and off-site Coulomb integrals, U and V.

Radical cation salts of EOPT-TTP, where EOPT-TTP is 2-(4,5-ethylenedioxy-1,3-dithiol-2-ylidene)-5-(4,5-propylenedithio-l,3 dithiol-2-ylidene) -1,3,4,6-tetrathiapentalene, have been prepared. All the salts obtained so far exhibited metallic temperature dependence of resistivity down to low temperature regardless of shape and size of counter anions.

EPR measurements of a new two-component organic conductor, (CHTM-TTP) 2 TCNQ, were performed. This salt shows two drastic successive phase transitions at low temperatures. The electronic phases of the title salt are discussed by microscopic point of view. The contributions of the two-spin species of the magnetic properties are separated. Possibility of cooperative phenomena in the two-spin system with itinerant and localised moments is discussed.

Selenium substitution of the outer 1,3-dithiole rings of TTM-TTP and TMET-TTP has been performed. The selenium analogues of TTM-TTP give the phases isostractural to (TTM-TTP)(I 3 ) 5/3 . The selenium substitution of the single outer ring does not suppress the 25 K transition, whereas the substitution of both outer rings affords a practically metallic phase.

Investigation of the extended Hubbard model considering the second nearest V in the atomic limit demonstrates the appearance of many patterns of charge-ordered states, even including Devil’s staircase at finite temperatures. This explains not only the observed modulations in θ-(BEDT-TTF) 2 RbZn(SCN) 4 above T MI , but also the first-order transition and the nearly temperature-independent resistivity. The same logic may be extended to many other organic conductors showing flat resistivity.

Several radical cation salts based on SMEO-ST-TTP and SMEO-TTP have been prepared. X-Ray structure analyses reveal that (SMEO-ST-TTP) 2 PF 6 has the so-called β-type donor packing, in which the donors are strongly dimerized in a stack. On the other hand, (SMEO-ST-TTP)Au(CN) 2 and (SMEO-TTP)Au(CN) 2 have strongly dimerized one-dimensional stacking structure. The PF 6 - and AsF 6 - salts based on SMEO-ST-TTP show metallic conductivity down to 22 and 90 K, respectively, below which resisitivity increases a little.

Conducting properties of various cation radical salts of the title donor have been investigated. Among them (TTM-TTP)I 3 and β-(TTM-TTP) 2 I 3 show metallic conductivity down to T MI = 160 and 20 K, respectively. The results of X-ray crystal structure analysis of (TTM-TTP)I 3 and (TTM-TTP)(PF 6 ) 0.267 (THF) 0.6 are also presented.

Organic donor TTM-TTP forms 1:1 composition salts with MX 4 (M = Fe, Ga; X = Cl, Br), which have dimerized one-dimensional columns and are insulators even at room temperature. On the Contrary, (TTM-TTP)FeBr 2 Cl 2 shows high electrical conductivity of about 1000 Scm -1 at room temperature and metallic behaviour down to 160 K. This salt has uniform one-dimensional donor columns. This is the first 1:1 composition organic metal with magnetic anion. The FeX 4 - salts exhibit weak magnetic interactions between the anions; the Weiss temperatures are less than 2.6 K.

Magnetic investigation of organic conductors based on TTP derivatives, (BDT-TTP) 2 SbF 6 and (EO-TTP) 2 AsF 6 , was carried out by 1 H-NMR measurements. The NMR spin-lattice relaxation rates, 1 H-T 1 -1 , of the present salts deviate from the Korringa-like behavior at low temperatures. The low-temperature electronic states of the TTP family will be discussed from microscopic points of view.

We present spectroscopic evidence for the charge disproportionation below the phase transition of the crystal of θ-(BDT-TTP) 2 Cu(NCS) 2 , This compound is a highly correlated quasi-2D organic conductor. Below the phase transition, the electronic transition in the mid-infrared region shifts to high-frequency side and the C=C stretching α g modes ν 2 , ν 3 , and ν 4 , which are sensitive to the charge on BDT-TTP, split into two groups. At 5 K these groups are reasonably assigned to charge-poor and charge-rich BDT-TTP molecules.

Using the heavy rare-earth complex anions, [Ln(NCS) 6 ] 3- (Ln = Ho, Er, Yb and Y), we have synthesized three series of metallic compounds, (BO) x [Ln(NCS) 6 ], (TTP) x [Ln(NCS) 6 ] (x = 8) and (DIEDO) 6 [Ln(NCS) 6 ]. The BO and TTP salts are metallic down to very low temperature, while the resistivity of the DIEDO salts increases below about 40 K. These are the first examples of stable metals based on organic π-donors and rare-earth 4f ions.

Ground states of one-dimensional organic conductors based on ChTM-TTP (2-(4,5-cyclohexylenedithio-1,3-dithiol-2-ylidene)-5-[4,5-bis(methylthio)-1,3-dithiol-2-ylidene]-1,3,4,6-tetrathiapentalene) have been investigated. (ChTM-TTP) 2 X (X = AuBr 2 , Au(CN) 2 , GaCl 4 ) shows antiferromagnetic phase transition around 30 K. The phase sequence of (ChTM-TTP) 2 X is similar to that of (TMTTF) 2 Br. The strength of the dimerization and the one-dimensionality controls the ground states of not only (ChTM-TTP) 2 X but also (TMTCF) 2 X.

Several derivatives of tris-fused donors, 2-(1,3-dithiol-2-ylidene)-2′-(thiopyran-4-ylidene)-5,5′-bi(1,3,4, 6-tetrathiapentalenylidene) (TPDT-TTPY) have been prepared. Cyclic voltammogram of the bis( n -hexylthio) derivative 1b showed four pairs of one-electron redox waves and a pair of two-electron redox one, which is in agreement with the existence of six redox-active sites. The first oxidation potential ( E 1 ) of 1b (+0.35 V vs. SCE) is almost equal to that of the corresponding derivative of the bis-fused donor TPDT-TTP ( 6 , +0.36 V). The E 2 - E 1 values of 1b (0.21 V) is smaller by ca. 0.04 V compared with that of 6 . The electrical conductivities of their conducting complexes are comparatively high (σ rt = 10 −2 - 10 0 S·cm −1 ).

A selenium analogue of dimethyl substituted TTP (DM-TS-TTP) was prepared. (DM-TS-TTP) 2 PF 6 showed metallic temperature dependence down to 4.2 K. X-Ray crystal structure analysis of this salt reveals that the arrangement of donors is similar to β-type BEDT-TTF salts. The band structure calculated by a tight-binding method suggests that it has a quasi one-dimensional Fermi surface.

A 1:1 composition organic conductor (TTM-TTP)I3 has a highly one-dimensional half-filled band, but shows a metallic conductivity down to 160 K. Another 1:1 composition organic conductor (TTM-TTP)[C(CN)3]has been prepared. This compound has a one-dimensional column similar to the I3− salt, but the packing pattern of the columns is different. This compound exhibits a metallic conductivity down to 70 K, an even lower temperature.

(TTM-TTP)(I3)5/3 (TTM-TTP: 2,5-bis[4,5-(methylthio)-1,3-dithiol-2-ylidene]-1,3,4,6-tetrathiapentalene) and its isostructual methylseleno-substituted compounds show metallic behavior above tmi ≈ 20 K in spite of large positive charge +5/3. High pressure resistivity and ESR measurements have been carried out. Both salts remain paramagnetic down to 2.9 K; no evidence of spin-Peierls or antiferromagnetic transition is obtained.

Preparation of a series of unsymmetrical tetrathiafulvalenes substituted with two methoxy groups (2a-f), and their electrochemical properties are described. X-Ray crystal structure analysis of methylenedithio derivative 2c reveals that there are side-by-side S…S contacts shorter than the sum of the van der Waals radii (3.70 a). The TCNQ complex of ethylendithio-2 (2d) and I3 salt of 2c showed low conductivity of 10−5 S cm−1 at room temperature.

We have synthesized several TTP (tetralhiapentalene) derivatives with a cyclohexane ring. Some of their salts show metallic conductivity, and have uniform stacks in spite of the bulky cyclohexane group. Among them (ChTM-TTP) 2 Au(CN) 2 exhibits a metal-insulator transition at 120 K, followed by a spin-Pcicrls or antiferromagnetic transition at 40 K. In addition thermoelectric power is consistent with semiconducting behavior and shows that the carriers arc holes on the donors.

Several derivatives of 2,2′-ethanediylidenebis(1,3-dithiole) fused with 1,3-dithiol-2-ylidenes (DT-EBDTs) have been prepared. Their cyclic voltammograms consist of three single-electron redox waves. The first redox potential of MeDT-EBDT (+0.37 V vs. SCE in PhCN) is lower by 0.08 V than those of the corresponding TTF, MeDT-TTF. On the other hand, the E 2 - E 1 value (0.13 V) is smaller by 0.18 V than that of MeDT-TTF. The present donors afford semiconducting AsF 6 − salts, TCNQF 4 and DDQ complexes (σ rt = 10 −5 =10 −1 S cm −1 , E a = 0.03–0.19 eV).

(TTM-TTP)I3, in sprite of its 1-D half-filled band, exhibits the metallic conduction at room temperature. Resistance, susceptibility, X-ray diffuse scattering studies revealed a phase transition at Tc ≈ 110 K below which the resistivity increases rapidly, the susceptibility decreases and the 2 kF = 0.5 c* superstructure sets in. The nature of the transition is discussed in the light of the band structure and the precursor effect at higher temperatures.

TTP (tctralhiapcntalcnc) scries donors have been prepared by two steps of phosphite-mediated cross-couplings. By using cyanoethyl groups instead of acctoxybenzyl as a protecting group, we have succeeded in improving the yields. The applicability of this method will be discussed.

2-(1,3-Diselenol-2-ylidene)-5-(pyran-4-ylidene)-1,3,4,6-tetrathiapentalene (PDS-TTP), its thiopyran analogue (TPDS-TTP), and their bis(methylthio) derivatives have been prepared. Their first and second oxidation potentials are comparable to those of the corresponding sulfur analogues. The PF 6 and AsF 6 salt of PDS-TTP displayed metallic conductivity down to 4.2 K, and TCNQ complex was semiconductor with a low activation energy (0.006 eV).

Observation of angle-dependece of magnetoresistance has been attempted for the bis-fused TTF analog of BEDT-TTF, β- (BEDT-TTP) 2 I 3 . The results are consistent with the calculated cylindrical Fermi surface, though the periodicity perpendicular to the conducting sheets is doubled owing to the superstructure of the anions.

BDT-TTP salts with tetrahedral anions show increase of resistivity below 200K at ambient pressure. This resistivity increase is accompanied by gradual increase of the magnetic susceptibility. Under high pressure the resistivity increase is suppressed.

Several BDT-TTP derivatives fused with benzene ( 1a-e ) and 1,2,5-thiadiazole ( 2c, f ) rings have been synthesized. Their cation radical salts and TCNQ complexes show high conductivity ( σ rt = 10 −1 −10 3 S cm −1 ). Among them, ClO 4 salt of 1d is metallic down to low temperature.

Several derivatives of alkyl-substituted DTEDT have been synthesized. Single crystals of cation radical salts of dimethyl-DTEDT ( 1Ab ) with octahedral anions showed high conductivities ( σ rt = 10 0 –10 1 Scm −1 ) and metal-like behavior around room temperature. The metal to insulator transition temperature tends to decrease as the volume of anions increases. The PF 6 , AsF 6 salts of cyclopenteno-DTEDT ( 1Ac ), and TaF 6 salt of tetramethyl-DTEDT ( 1Bb ) show metallic conducting behavior down to 50 K.

The electrical resistivity of (DTEDT) 3 SbF 6 shows a metallic temperature dependence down to 10 K. After showing a resistance minimum, the resistivity increases with log T dependence, which is followed by a decrease below ∼0.2 K. The log T dependence is ascribed to weak localization in two-dimensional system. The decrement was suppressed by a magnetic field less than ∼1 T, suggesting that it is due to a superconducting transition.