Y. Misaki

Low temperature X-ray and ESR study of one-dimensional compound (TTM-TTP)I3

Abstract (TTM-TTP)I 3 which has been considered as the typical one-dimensional half-filled band system, has been critically restudied by structural and magnetic measurements. X-ray diffuse scattering study reveals the formation of 2 k F CDW superstructure with the wave vector q 1 =(0, 0, 0.5) below 160 K of the metal-insulator transition temperature. Another structural modulation with q 2 = (0.5, 0, 0.5) is observed below 90–100 K. Modulated structure analysis using the q 2 satellite reflections and the Bragg reflections shows the large displacement in I 3 anion. Anomalies in χ, line width and g -value of ESR measurements which correspond to the structural anomaly, are also reported.

Two-Dimensional Band Structure of Organic Metals (BDT-TTP)2X (X=SbF6, AsF6) Studied by Polarized Reflection Spectroscopy

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...

Assignment of the in-plane molecular vibrations of the electron-donor molecule BDT-TTP based on polarized Raman and infrared spectra, in which BDT-TTP is 2,5-bis(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene

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.

Theoretical estimation of the electron-molecular vibration coupling in several organic donor molecules

Abstract 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.

Metal-insulator transition of the 1-D half-filled band metal (TTM-TTP)I3

Abstract (TTM-TTP)I 3 , 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 T c ≈ 110 K below which the resistivity increases rapidly, the susceptibility decreases and the 2 k F = 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.

Syntheses and properties of genuine organic magnetic conductors: (1:1) and (1:2) salts of ethyl-pyridinium-substituted verdazyl radicals with TCNQ

Abstract 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.

π-f Composite metals

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.

Charge disproportionation in the charge-transfer salts of TTP

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.

Synthesis, Structures And Properties Of Cyclopenteno Annelated Bis-Fused TTF Donors And Their Molecular Complexes

Abstract A series of cyclopenteno annelated bis-fused TTF derivatives (CP-TTP 1a-d) have been synthesized. The present donors have produced many molecular complexes showing high conductivity. In particular, several cation radical salts based on the bis(methylthio)- (CPTM-TTP 1c) and ethylenedithio (CPET-TTP, 1d) derivatives are metallic down to liquid helium temperature, though resistivity of CPTM-TTP salts increases a little at low temperature. Among metallic salts, (CPTM-TTP)4X (X = PF6 −, AsF6 − and SbF6 −) are isostructural and have two-dimensional “β-type” arrangement of donor molecules. The band calculations of these salts indicate they have eclipsed Fermi surfaces characteristic of two-dimensional metals.

Facile preparation of TTP series donors by using cyanoethyl groups

Abstract 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.