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Crystal polymorphs of fluorinated ionic liquids (fILs) were examined at low-temperature (LT) by Raman spectroscopy. The fILs were 1-alkyl-3-methylimidazolium perfluorobutanesulfonate, [C

We have employed 1,7-dibromo-N,N’-ditridecyl-3,4,9,10-perylenetetra carboxylic diimide (DB-PTCDI-C13) for the development of novel n-type monolayer field-effect-transistor (FET). Functionalization of PTCDI core with long alkyl chain and bulky bromine atoms improved the solubility and made n-type monolayer FET performance possible via solution deposition processes. Annealing effect of spin coated films and drop casted films have been discussed. Liquid crystalline phase of DB-PTCDI-C13 turned out to be playing an important role in controlling the film quality and mobility. The highest mobility was 5.8 × 10−3 cm2 V−1 s−1 after annealing, of which device has been then tested for doping by potassium.

Single crystals of 4,5-ethylenedioxy-4′-iodotetrathiafulvalene (EDO-TTF-I) with iodine bonding ability were obtained by recrystallization from acetonitrile and crystallized in the orthorhombic system with the space group Pbca. Bent EDO-TTF-I molecules formed the dimer structure, and a short I⋯O contact was observed between dimers. Electrocrystallization of EDO-TTF-I in absolute ethanol containing tetrabutylammonium hexafluorophosphate, (TBA)PF6, afforded single crystals of (EDO-TTF-I)2PF6. An X-ray structural analysis revealed that EDO-TTF-I molecules form dimerized stacking columns in a head-to-tail manner, which is referred to as a β′-type arrangement. Iodine bonds between EDO-TTF-I and PF6 anions and short I⋯S contacts between EDO-TTF-I molecules were observed. Tight-binding band calculations indicated that the strong molecular dimerization splits the energy band into upper and lower bands with a small energy gap, where the upper band is effectively half-filled. It was found that (EDO-TTF-I)2PF6 is semiconducting (σRT = 5.3 S cm−1 and Ea = 0.17 eV) and exhibits magnetic properties reminiscent of a low-dimensional localized spin system. The magnetic data were analyzed by the Bonner–Fisher model incorporating interchain interactions: |J|/kB = 67.1 K and zJ′/kB = −61.1 K. No splitting of the CC stretching modes was observed in the range of 5–300 K by Raman spectroscopy, indicating a homogeneous charge distribution of EDO-TTF-I0.5+. Therefore, (EDO-TTF-I)2PF6 is considered as a dimerized Mott insulator.

The valence state of ionic molecular solids composed of biferrocene derivatives (D) and tetracyanoquinodimethane (TCNQ) derivatives (A), either monovalent ([D](+)[A(2)](-)) or divalent ([D](2+)[A2](2-)), can be controlled by changing the redox potentials and molecular volumes of the components.

We report IR and Raman spectra for a two-dimensional superconductor, β′′-(BEDT-TTF)4[Ga(C2O4)3(H3O)]C6H5NO2, below the superconducting transition temperature. The behavior of the lattice-sensitive ...

(MDABCO(+))(C60(·-))(TPC) (1), in which MDABCO(+) is N-methyldiazabicyclooctanium, TPC is triptycene, and both have threefold symmetry, is a rare example of a fullerene-based quasi-2D metal and contains closely packed hexagonal fullerene layers with interfullerene center-to-center distances of 10.07 Å at 300 K. Evidence for the metallic nature of 1 was obtained by optical and microwave conductivity measurements on single crystals. The metal is characterized by a nontypical Drude response and relatively large optical mass (m*/m0 =6.7). The latter indicates a narrow-band nature, which is consistent with the calculated bandwidth of 0.10-0.15 eV. The coexistence of metallic and antiferromagnetic nonmetallic 2D layers was observed in 1 above 200-230 K. It was assumed that the nonmetallic layers undergo a transition to the metallic state below 200 K due to ordering of the fullerene and cationic sublattices. New layered complex (MQ(+))(C60(·-))(TPC) (2) with a hexagonal arrangement of C60(·-) was obtained by increasing the interfullerene distance with the bulkier N-methylquinuclidinium cations (MQ(+)) having threefold symmetry. The structure of 2 is characterized by increased interfullerene center-to-center distances in the layers (10.124, 10.155, and 10.177 Å at 250 K). Unit-cell doubling parallel to the 2D layer (along the b axis) was observed at low temperatures. In contrast to metallic 1, 2 exhibits a nonmetallic spin-frustrated state with an antiferromagnetic interaction of spins (the Weiss temperature is -27 K) and no magnetic ordering down to 1.9 K. It was supposed that the expanded interfullerene distances in the triangular arrangement decrease the bandwidth and suppress metallic conductivity in 2, and thus a Mott-Hubbard insulating state with antiferromagnetically frustrated spins results.

Compounds of the formula (EDO-TTF-Cl)2XF6 (EDO-TTF-Cl = 4-chloro-4′,5′-ethylenedioxytetrathiafulvalene, X = As, Sb) were prepared to examine the substituent size effect on the packing structure of the donor molecules. In these salts, a head-to-tail type donor stacking was observed. Although the AsF6 salt is a quasi-one-dimensional dimer Mott insulator, the SbF6 salt shows quasi-one-dimensional metallic behavior. Detailed crystal structure analyses revealed the correlation between the anion size and the intermolecular slipping among the donor molecules. The donor morphology, which plays an important role in the overlapping mode selectivity, is characterized by the magnitude and configuration of the out-of-plane substituent size.

Polycrystalline powders of Cu(TCNQ) (TCNQ = 7,7′,8,8′-tetracyanoquinodimethane) absorb iodine to form Cu(TCNQ)I4 upon solid grinding with iodine or immersion in a hexane solution of iodine. Of the two polymorphs of Cu(TCNQ), phase II Cu(TCNQ) exhibits a much slower iodine-absorption rate than that of phase I Cu(TCNQ) in the liquid-phase reaction, whereas the solid grinding reaction results in efficient absorption for both phases. The valence state of the iodine-containing salt is [Cu+I−(TCNQ0)](I2)1.5, where the copper ion is coordinated with an iodide anion and neutral TCNQ. The salt is a semiconductor (σRT = 3 × 10−3 S cm−1, compaction pellet) with an electrical conductivity one order lower than that of Cu(TCNQ). The salt releases iodine by annealing to regenerate the original phases of Cu(TCNQ) via an intermediate Cu(TCNQ)I state. A solid-state reaction of TCNQ, CuI, and iodine also produces the iodine-containing salt. The iodine absorption–desorption mechanism of Cu(TCNQ) differs from that of alkali-TCNQ salts that we reported previously.

Alkali metal salts of 7,7′,8,8′-tetracyanoquinodimethane (TCNQ) reversibly absorb iodine forming the ternary salts M(TCNQ)I (M = Li, Na, K) and M2(TCNQ)3I2 (M = Rb). The ternary salts are also obtained by solid-state reactions of TCNQ with alkali iodides. These salts are paramagnetic and have high electrical conductivities, ∼10−1 S cm−1, for compacted pellets, whereas the alkali metal salts of TCNQ are diamagnetic insulators. The ternary salts further absorb iodine to give over-doped salts M(TCNQ)In (n ≈ 6, M = Na, K), which gradually release iodine to give M(TCNQ)I. In contrast, the solid-state reaction of F4TCNQ and sodium iodide produces Na(F4TCNQ), which does not exhibit iodine absorption.

[Dineopentyl-biferrocene]2[Cl1TCNQ]7, which has an unprecedented high donor-acceptor ratio of 2 : 7, contains a linear paramagnetic hexamer of Cl1TCNQ. Both the donor and acceptor molecules exhibit charge disproportionation in the crystal through mutual electrostatic interactions.

Superconducting (SC) devices are attracting renewed attention as the demands for quantum-information processing, meteorology, and sensing become advanced. The SC field-effect transistor (FET) is one of the elements that can control the SC state, but its variety is still limited. Superconductors at the strong-coupling limit tend to require a higher carrier density when the critical temperature (TC ) becomes higher. Therefore, field-effect control of superconductivity by a solid gate dielectric has been limited only to low temperatures. However, recent efforts have resulted in achieving n-type and p-type SC FETs based on organic superconductors whose TC exceed liquid He temperature (4.2 K). Here, a novel "ambipolar" SC FET operating at normally OFF mode with TC of around 6 K is reported. Although this is the second example of an SC FET with such an operation mode, the operation temperature exceeds that of the first example, or magic-angle twisted-bilayer graphene that operates at around 1 K. Because the superconductivity in this SC FET is of unconventional type, the performance of the present device will contribute not only to fabricating SC circuits, but also to elucidating phase transitions of strongly correlated electron systems.

The kinetic energy of α′-(BEDT-TTF)2IBr2, α-(BEDT-TTF)2I3, and α-(BEDT-TTF)2NH4Hg(SCN)4 was estimated from the room-temperature optical conductivity measured from 50 to 30 000 cm−1. The kinetic energy of α′-(BEDT-TTF)2IBr2 was significantly smaller than that of α-(BEDT-TTF)2I3 that shows metal–insulator phase transition. A clear hysteresis was found in the magnetic susceptibility near the phase transition at around 30 K.

An organic conductor θ -(BTM-TTP) 2 SbF 6 , where BTM-TTP denotes 2-[4,5-bis(methylthio)-1,3-dithiol-2-ylidene]-5-(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene, is semiconducting and shows Curie–Weiss-like magnetism, whereas the X-ray structure shows that all BTM-TTP molecules are crystallographically equivalent and the tight-binding band calculation affords the closed Fermi surface. We have studied the electrical properties and Raman spectra of θ -(BTM-TTP) 2 SbF 6 in order to clarify the origin of the carrier localization. From the electrical resistivity measurement, the maximum of activation energy appeared at ca. 240 K. Raman spectroscopy reveals the charge disproportionation in θ -(BTM-TTP) 2 SbF 6 from room temperature, and the degree of charge disproportionation is estimated to be +0.0 3 ∼0.1 3 :+0.9 3 at 6 K.

Ternary radical cation salts containing ethylenedioxytetrathiafulvalene, its mono-methyl substituted derivative, and hexafluorophosphate, [(EDO-TTF) 1– x (MeEDO-TTF) x ] 2 PF 6 ( x =mole fraction of MeEDO-TTF, x =0.01–0.13) were prepared by electrooxidation. Mole fractions of EDO-TTF and MeEDO-TTF in EDO-TTF rich alloys were consistent with the donor mixing ratios in preparation. Crystal structures of these alloys at room temperature were isostructural to that of (EDO-TTF) 2 PF 6 , where the donor molecules formed a nearly uniform stacking column to give a quasi-one-dimensional Fermi surface. The alloys exhibited a metal–insulator transition with tetramerization within the donor stack and anion-ordering. Temperature-variable structural analysis and Raman spectra revealed that the charge-ordering took place in the low temperature phase of x =0.05 alloy, however, this feature vanished in the x =0.13 alloy. The phase transition temperature decreased with increasing x value from 279 K of pristine (EDO-TTF) 2 PF 6 to 188 K of x =0.13 alloy.

Electrocrystallization of 2-(thiopyran-4-ylidene)-4,5-ethylenedithio-1,3-dithiole (TP-EDTT) in an electrolytic solution containing tetrabutylammonium hexafluoroantimonate afforded black elongated platelets of (TP-EDTT) 2 SbF 6 . (TP-EDTT) 2 SbF 6 crystallized in a triclinic system with space group P 1 ¯ : a =6.496(2), b =7.197(3), c =15.294(4) A, α =95.58(3), β =102.09(2), γ =101.41(2)°, V =678.1(4) A 3 , Z =1, and R =0.035 ( I ≥2 σ ( I )). One TP-EDTT molecule and one half SbF 6 anion were crystallographically unique. TP-EDTT molecules formed a dimerized one-dimensional stacking column along the b -axis with a head-to-tail manner. Short S⋯S contacts were observed between ethylenedithio-1,3-dithiole moieties of adjacent molecules along the molecular short axis, and short S⋯F and H⋯F contacts were also observed between the thiopyran ring of TP-EDTT molecule and SbF 6 anion along the molecular long axis. Tight-binding band calculation afforded the effective half-filled band structure due to the strong dimerization. The electrical resistivity showed semiconductive temperature dependence from room temperature ( σ RT =6.1×10 −1 S cm −1 , E a =92 meV). Raman spectroscopy revealed no sign of charge disproportionation in the range from 300 to 6 K. (TP-EDTT) 2 SbF 6 is considered to be a dimer Mott insulator.

Electrocrystallization of a mixture of 4,5-ethylenedioxytetrathiafulvalene (EDO-TTF) and 4,5-ethylenedioxy-4′-methyltetrathiafulvalene (MeEDO-TTF) yielded alloyed salts, [(EDO-TTF)1−x(MeEDO-TTF)x]2PF6 (x = mole fraction of MeEDO-TTF). EDO-TTF rich alloys (x ≤ 0.5) were isostructural to (EDO-TTF)2PF6, the metal−insulator transition of which is caused by the cooperation of Peierls, anion-ordering, and charge-ordering mechanisms. Incorporation of MeEDO-TTF into (EDO-TTF)2PF6 extended the donor−anion distance to weaken donor−anion interactions, while donor−donor interactions within the conduction layer remained the same magnitudes to those of (EDO-TTF)2PF6 having a quasi-one-dimensional electronic structure. These alloys showed a metallic behavior or nearly constant resistivity around room temperature, and their transport properties strongly depended on x value. x ≤ 0.13 alloys showed a sharp metal−insulator transition due to Peierls instability and anion-ordering, and transition temperature decreased as x in...

Photoirradiation of a solution of BH(3).NHR(2) (1a: R = Me, 1b: R = 1/2C(4)H(8), 1c: R = 1/2C(5)H(10), 1f: R = Et) containing a catalytic amount of a group-6 metal carbonyl complex, [M(CO)(6)] (M = Cr, Mo, W), led to dehydrogenative B-N covalent bond formation to produce aminoborane dimers, [BH(2)NR(2)](2) (2a-c, f), in high yield. During these reactions a borane sigma complex, [M(CO)(5)(eta(1)-BH(3).NHR(2))] (3), was detected by NMR spectroscopy. Similar catalytic dehydrogenation of bulkier amineboranes, BH(3).NH(i)Pr(2) (1d) and BH(3).NHCy(2) (1e, Cy = cyclo-C(6)H(11)), afforded monomeric products BH(2) horizontal lineNR(2) (4d, e). The reaction mechanism of the dehydrocoupling was investigated by DFT calculations. On the basis of the computational study, we propose that the catalytic dehydrogenation reactions proceed via an intramolecular pathway and that the active catalyst is [Cr(CO)(4)]. The reaction follows a stepwise mechanism involving NH and BH activation. Dehydrocoupling of borane-primary amine adducts BH(3).NH(2)R (1g: R = Me, 1h: R = Et, 1i: R = (t)Bu) gave borazine derivatives [BHNR](3) (5g-i).

Recently we succeeded in the isolation of delocalized singlet biradicals utilizing the spin-delocalizing character of the phenalenyl radical. We demonstrated that the singlet biradical 1 has strong spin–spin interactions between molecules through the overlap of phenalenyl rings in the onedimensional (1D) chain even though the closed-shell Kekul structure 1 can be drawn as a resonance contributor (Scheme 1). Huang and Kertesz gave further insight into the spin–spin interactions from a theroretical point of view and showed that the spin–spin interaction between the molecules was predicted to be stronger than that within the molecule. These experimental and theoretical findings are associated with very fundamental issues: Do delocalized singlet biradicals actually have open-shell character? Are the electrons coupled within a molecule involved in covalent bonding between molecules? In this study we will demonstrate that intraand intermolecular spin–spin interactions strongly correlate and can be altered in magnitude by an applied external field. Our proposal is based on the experimentally determined molecular structure of 2, a temperature-dependent reflection spectrum of 2, and a pressuredependent reflection spectrum of 1. Methyl groups at the 2and 10-positions in 2, where the frontier molecular orbital has very small coefficients, are expected to alter the distance between the overlapping phenalenyl rings with respect to the analogous separation in 1, and as a result, the magnitude of the intermolecular spin–spin interaction should be affected. The synthesis of 2 is outlined in Scheme 2. The 3,10and 3,11-bis(bromomethyl) compounds 3 were synthesized according to the previously reported procedures. The individual isomers were not isolated because both were expected to lead to the single compound 2. Bis(2-methylpropionic acid) derivatives 5 were obtained in three steps by standard methods. Friedel–Crafts cyclization of the acyl chloride derivatives of 5 with AlCl3 afforded diketones 6. These were reduced with NaBH4 and subsequently dehydrated with a catalytic amount of p-toluenesulfonic acid to afford the dihydro compounds 8. Dehydrogenation of 8 with p-chloranil afforded the hydrocarbon 2 as green prisms. Compound 2 was found to be stable in the solid state at room temperature. The small HOMO–LUMO gap of 2, which is an essential factor for a singlet biradical electronic structure, was confirmed by electrochemical and optical methods. The cyclic voltammogram of 2 shows four reversible redox waves: E 2 = + 0.51, E 1 =+ 0.11, E red 1 = 1.09, and E 2 = 1.62 (V vs. ferrocene/ferrocenium couple (Fc/Fc), see Figure S1 in the Supporting Information), which led to an electrochemical HOMO–LUMO gap of 1.20 eV. The electronic absorption spectrum of 2 in CH2Cl2 shows an intense low-energy band at 756 nm (13200 cm = 1.64 eV, e= 115000, f= 0.605, see Scheme 1. Resonance structures of 1 and 2. The arrows in the biradical structure represent antiparallel spins.

The partially deuterated 4,5-ethylenedioxy-tetrathiafulvalene-d2 (EDO-TTF-d 2 ) was synthesized from the undeuterated EDO-TTF-d o . The single crystals of (EDO-TTF-d 2 XF 6 (X = P, As) were prepared by the conventional electrocrystallization technique. The deuterium contents of EDO-TTF-d 2 itself and the radical cation salts were 99% D by mass spectral analysis. The magnetic susceptibility measurement revealed that (EDO-TTF-d 2 ) 2 XF 6 undergoes a metal-insulator transition at 2-3 K higher temperature than the undeuterated salts. In infrared and Raman spectra, significant isotope shifts were observed not only on C-H vibrational modes but also on TTF-skeletal modes. The assignment of experimental bands was performed on the basis of normal-mode analysis at B3LYP/6-31G(d,p) level of theory.

Electrochemical oxidation of 4,5-ethylenedioxy-4′-methyl-tetrathiafulvalene (MeEDO-TTF) afforded three types of (MeEDO-TTF)2PF6 radical cation salts under different conditions: black powder, dark green plates, and black plates. The optical absorption spectra of these modifications were very similar to each other. The black powder and dark-green plate modifications were semiconducting and metallic, respectively, and the latter showed a semiconducting behavior below 200 K. The black plate modification exhibited a semiconductor-to-semiconductor first-order phase transition at around room temperature (303 K). The donor molecules in both the high- and low-temperature phases of this modification showed similar packing patterns, based on which the tight-binding approximation afforded similar two-dimensional Fermi surfaces. The phase transition of this modification is accompanied by a subtle change in the relative orientation of the neighboring donor molecules. The vibrational spectra proved that a nearly localiz...

We prepared and isolated a phenalenyl-based neutral hydrocarbon (1 b) with a biradical index of 14%, as well as its charge-transfer (CT) complex 1 b-F(4)-TCNQ. The crystal structure and the small HOMO-LUMO gap assessed by electrochemical and optical methods support the singlet-biradical contribution to the ground state of the neutral 1 b. This biradical character suggests that 1 b has the electronic structure of phenalenyl radicals coupled weakly through an acetylene linker, that is, some independence of the two phenalenyl moieties. The monocationic species 1 b*+ was obtained by reaction with the organic electron acceptor F4-TCNQ. The cationic species has a small disproportionation energy deltaE for the reaction 2 x 1 b*+ 1 b + 1 b2+, which presumably originates from the independence of the phenalenyl moieties. The small deltaE led to a small on-site Coulombic repulsion U(eff) = 0.61 eV in the CT complex. Moreover, a very effective orbital overlap of the phenalenyl rings between molecules afforded a relatively large transfer integral t = 0.09 eV. The small U(eff)/4t ratio (= 1.7) resulted in a metallic-like conductive behavior at around room temperature. Below 280 K, the CT complex showed a transition into a semiconductive state as a result of bond formation between phenalenyl and F4-TCNQ carbon atoms.

The family of materials (EDO-TTF)2XF6 represents quasi-one-dimensional ¼ filled systems exhibiting insulator-to-metal (I-M) phase transition at thermal equilibrium. (EDO-TTF)2PF6 is known to undergo a photoinduced I-M conversion with cooperative response to light excitation. Here we use femtosecond pump-probe experiments to study the photoresponse of (EDO-TTF)2SbF6 made of a larger counter-anion SbF6 compared to the well studied (EDO-TTF)2PF6. In the early stage of the photoinduced process, we reveal a multi-component coherent oscillating feature. The evolution of this feature with excitation density and temperature points to the local nature of the photoswitching in (EDO-TTF)2SbF6. At longer timescale, we did not detect the features associated with the transformation to the M phase, albeit observed in the PF 6 derivative. We propose a scenario whereby the bigger size of the counter-anion in (EDO-TTF)2SbF6 hinders the establishment of this transformation at macroscopic scale.

A new π-donor, 4-chloro-4′,5′-ethylenedioxytetrathiafulvalene (CLEDO-TTF) was synthesized from 4-methoxycarbonyl-4′,5′-ethylenedioxytetrathiafulvalene in the yield of 85%. In the crystal of neutral molecule, the head-to-head type uniform stacking column, in which the donor molecules are related by a unit cell translation, was formed. The electrocrystallization of CLEDO-TTF with PF6 afforded two kinds of 1:1 salts of purple rods and green plates as miner species. In both 1:1 salts, the head-to-tail dimers with ring-over-ring overlapping mode were formed. Geometrically, the dimers were included in slipped stacking column in the purple rod salt, while the two-dimensional network was formed in the green plate salt. The significant steric effect of chlorine atom along the molecular long axis was confirmed by the intermolecular arrangement in the green plate salt, in which the chlorine atom is faced to the hydrogen atom of the neighbouring donor along the long axis. The normal mode analyses were carried out for the neutral and monocationic CLEDO-TTF, which agreed well with the observed Raman spectra. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

(1) Research Center for Low Temperature and Materials Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan

Raman spectra of (Me 2 -DCNQI) 2 Cu x Li 1- x (0≤ x ≤1) have been measured at room temperature, 200 K, 100 K and 5 K. The observed Raman bands are assigned on the basis of the vibrational analysis done by Lunardi and Pecile. The Raman band assigned to the a g v R8 fundamental mode (quinoid C=N stretching) shifts downward with an increase of x and exhibits a remarkable split for 0≤ x ≤0.29. This frequency shift is attributable to the change of a charge density on a Me 2 -DCNQI molecule. From the split of the v R8 Raman band, it is concluded that the charge densities on Me 2 -DCNQI molecules are not equivalent even at room temperature for 0≤ x ≤0.29.

We present the low-temperature crystal structures of (BDTFP)2PF6 and (BDTFP)2AsF6 below the phase transition temperatures (Tp). In the former compound, the c-axis is doubled, and the dimerized structure is therefore changed into a tetramerized structure. At the same time, a new charge-transfer transition appears at ca. 7000–8000 cm−1. These two findings are consistent with the non-magnetic state below Tp. In the latter compound, on the other hand, the dimerized structure is maintained below Tp, and the AsF6 ion rotates along with the ca. 10° rotation of BDTFP. This structural change is the origin of the first-order phase transition to a paramagnetic state.

Magnetic investigation was carried out for quasi-one-dimensional organic conductors, (BDTFP) 2 X (PhCl) 0.5 ( X =AsF 6 , PF 6 ). They show Metal-Insulator transitions at low temperatures. To clarify the mechanism of the transitions, we performed ESR and NMR measurements. The low temperature electronic states of the title compounds are discussed by a microscopic point of view.

The mixed crystal system Co x Ni 1-x Pc(AsF 6 ) 0.5 (0

New bis(1,3-dithiole) electron donors containing a cyclohexene unit were prepared using a Wittig-Honer reaction and a cycloreversion reaction. The tetramethyl derivative afforded the highly conductive cation radical salts as single crystals whose unusual crystal structures were revealed by X-ray analysis.

The accurate degree of charge transfer (CT) of BO complexes was obtained by Raman spectroscopy. A rich variety of states with partial CT in a wide range were available for BO materials, either due to stoichiometry or incomplete CT. Above certain acceptor strength, in the complex with BO there is a tendency for the acceptor to be ionized to the fully ionic state of −1 regardless the redox potential in general. The transport properties of BO complexes were discussed in terms of CT degree.

The organic alloy, CoxNi1 − xPc(AsF6)0.5 (0

Raman spectroscopy was employed as a fast and exact general method to determine the charge on BEDO-TTF (BO) in its complexes in any sample form such as single crystals, powders, and dispersed polym...

We present the metal–insulator (MI) transition of the title compounds examined by reflection spectroscopy, X-ray diffraction, and magnetic susceptibility. Below the MI transition temperature, the space group changes from P2 1 / a to Pa with 4k F lattice modulation in (BEDT-ATD) 2 PF 6 (DHF) and (BEDT-ATD) 2 BF 4 (THF) which undergo MI transitions at 150 K and 200 K, respectively. On the other hand, the symmetry change is not observed at about 80 K in (BEDT-ATD) 2 PF 6 (DO) ( T MI =100 K), (BEDT-ATD) 2 PF 6 (THF) ( T MI 2 AsF 6 (THF) ( T MI F lattice modulation is supported by the magnetic susceptibility experiment as well. The precursor phenomenon of this structural change is observed already at room temperature in (BEDT-ATD) 2 PF 6 (DO). All of these data suggest the view that (BEDT-ATD) 2 X(solvent) is a strongly correlated 1D metal.

We present the polarized reflection spectra of (BEDT-ATD)2X(solvent) (X = AsF6, PF6, BF4; solvent = THF, DHF, DO), where THF is tetrahydrofuran, DHF 2,5-dihydrofuran, and DO 1,3-dioxolane. BEDT-ATD+ has an intramolecular excitation in a very low-energy region (4000–5000 cm−1). These isostructural compounds are characterized as strongly correlated quasi-1D metals. The optical spectra in all these compounds suggest that the screw-axis symmetry is broken below the metal–insulator transition temperature. This broken symmetry is confirmed by the X-ray diffraction experiment in (BEDT-ATD)2BF4(THF) and (BEDT-ATD)2PF6(DHF). The low-temperature structure has the 4kF-modulated lattice (dimerized structure). The magnetic susceptibility supports this 4kF modulation as well. We present the low-temperature crystal structures of (BEDT-ATD)2BF4(THF) and (BEDT-ATD)2PF6(DHF). BF4− and THF are fully ordered in (BEDT-ATD)2BF4(THF) and DHF is almost ordered in (BEDT-ATD)2PF6(DHF). The vibronic modes are observed in the reflection spectra of all these compounds even above the metal–insulator transition temperature, which suggests that the screw-axis symmetry is locally broken.

Photolysis of [M(CO)6] (M = Cr, W) in the presence of BH3·L (L = NMe3, PMe3, PPh3) gave isolable borane complexes [M(CO)5(η1-BH3·L)] (1a, M = Cr, L = PMe3; 1b, M = Cr, L = PPh3; 1c, M = Cr, L = NMe3; 2a, M = W, L = PMe3; 2b, M = W, L = PPh3; 2c, M = W, L = NMe3). In products 1 and 2, the monoborane−Lewis base adduct coordinates to the metal center through a B−H−M three-center two-electron bond, which was confirmed by X-ray structural analyses of 1a, 2a, and 2b at low temperature. The X-ray crystal structural analysis of 1c at ambient temperature also showed the same coordination mode, although the positions of hydrogen atoms on the boron were not determined. The 1H NMR spectra of 1 and 2 exhibit only one BH signal at −2 to −3 ppm with an intensity of 3H in the temperature range of −80 °C to room temperature. This indicates that the coordinated BH and terminal BH's are rapidly exchanging in solution even at low temperature. When [Mo(CO)6] was used as a precursor, the formation of the corresponding molybden...

The polarized reflection spectrum indicates that the organic metal (BEDT-ATD) 2 PF 6 (THF) has a quasi-one-dimensional band structure with a narrow bandwidth of ca. 0.24 eV. The intra-HOMO-band transition of (BEDT-ATD) 2 PF 6 (THF) shows two broad peaks at ca. 1000 cm -1 and 1700 cm -1 which feature is quite different from the Drude-like metallic absorption. The vibronic bands interfering with this absorption band begin to grow as dips at 100 K, which means that the screw-axis symmetry of the space group P 2 1 / a is broken below 100 K. This broken symmetry is supported by the splitting of the Raman band of a charge-sensitive vibrational mode. It is suggested from the comparison with the thermopower's data that this structural change has no long-range-ordered modulation above 50 K. The intensity of some infrared-active vibrational modes is enhanced by the intra-molecular charge oscillation whose optical transition appears at 4600 cm -1 .

The synthesis, crystal structure and physical properties of a new bedt-ttf charge transfer salt containing the tris(oxalato)germanium(IV) anion are described and interpreted. Electrochemical oxidation of neutral bedt-ttf in the presence of (NH4)2Ge(C2O4)3·2H2O in PhCN solution yields crystals of (bedt-ttf)2Ge(C2O4)3·PhCN. The crystal structure has been solved at 296(2) and at 120(2) K. In contrast to the well known tris(oxalato)-metallate(III) salts of bedt-ttf, the structure does not contain alternating layers of bedt-ttf cations and tris(oxalato)metallate anions, but consists of a ‘checker board’ arrangement of face-to-face bedt-ttf dimers with [Ge(C2O4)3]2– interspersed by layers of solvent molecules. Each bedt-ttf molecule has a charge close to +1, which is estimated from the empirical relationship between CC and C–S bond lengths and these charges are correlated with Raman spectra. As expected from the presence of strongly dimerised (bedt-ttf+)2 units the salt is a semiconductor between 300 and 120 K with a low activation energy of 0.127 eV.

We investigated the Hall effect, the transverse magnetoresistance, the optical reflectivity and the ultraviolet photoelectron spectra for 1st and 2nd stage KO x -GICs (C 4 n KO x , stage number n =1, 2; x ∼2) in order to clarify the transport properties and the electronic structures. The Hall effect and the magnetoresistance indicate that the electrical conduction in KO x -GICs is governed by the majority electron carriers with low mobility in graphitic π bands and the minority hole carriers with high mobility in the intercalate bands, the latter of which originates mainly from the oxygen bands as suggested by the incident photon energy dependence of the ultraviolet photoelectron spectra. The optical reflectance spectra give the estimates of the Fermi energies, 1.9 eV and 1.35 eV for 1st and 2nd stage compounds, respectively, on the basis of the Drude-Lorentz model. The contribution of the intercalate hole carriers to the plasma frequency is small in good agreement with the Hall effect indicating the pres...

The IR and Raman spectra of β″-(ET)3X2 [X = HSO4 and ClO4] salts were measured at various temperatures below 300 K. The ν2 and ν27 modes exhibit the splitting into two peaks below the metal–insulator transition temperature. This phenomenon is ascribed to the charge ordered (CO) state. The CO patterns of the presented compounds were determined on the basis of the numerical calculation of the vibronic ν3L mode. The assignment of the ν27 mode of ET+ was confirmed through the measurement of the reflectance spectra of the 1:1 salts (ET)ClO4, (ET)AuCl2Br2 and the isotope analogues. The ν27 mode is the efficient probe to the site charges of the ET salts.

The neutral molecule, monocation, and dication of BDNT, which shows a one-step two-electron oxidation property, were characterized by a spectroscopic method. The extreme closeness of the first and second oxidation potentials is ascribable to the large structural change from BDNT1+ to BDNT2+. The on-site Coulomb energy U and transfer integral t of monoclinic BDNT-PF6 were estimated to be 0.8 eV and 0.13 eV, respectively. The coupling constants of the vibronic band were estimated by the least-squares fitting of the dimer-model function to the observed conductivity spectrum. These coupling constants shows that BDNT1+ is rather rigid compared with TTF, TCNQ, or Chloranil.

We We present the temperature dependences of the reflectance and Raman spectra of metallic β-(BEDT-TTF)(TCNQ). BEDT-TTF and TCNQ form quasi-one-dimensional bands mainly extended along the a- and c-axes, respectively, and their interaction along the b-axis is weak. The degree of charge transfer from BEDT-TTF to TCNQ is about 0.5, so that each band forms a 3/4- and 1/4-filled band. With lowering temperature, the optical conductivity associated with BEDT-TTF band approaches a Drude-like shape without structural distortion. On the other hand, the optical conductivity of TCNQ band deviates from a Drude-like response with a 2k F or 4k F lattice distortion. At room temperature, the Raman-active ν 2 and infrared-active ν 27 modes of BEDT-TTF showed a splitting, that is, the charge on the BEDT-TTF chain is nearly localized. Interestingly, these split bands merged at around 100 K. The Raman-active ν 4 of TCNQ keeps the frequency corresponding to TCNQ 0.5- . Therefore, the charge in TCNQ column is equally sheared by two or four TCNQ molecules.

We studied C=C stretching bands of β'=(ET) 3 (ReO 4 ) 2 and β-(ET) 4 M(CN) 4 H 2 O (M=Pt, Pd and Ni) at the low temperatures below 300 K in order to verify the inhomogeneous charge distributions. A drastic spectral change was observed for β-(ET) 3 (ReO 4 ) 2 at 80 K, below which the system falls into the charge ordered state. On the other hand, a continuous spectral change was observed for β-(ET) 4 Ni(CN) 4 H 2 O and β-(ET) 4 Pd(CN) 4 H 2 O. ν 2 for M=Ni and Pd exhibited a doublet, suggesting an inhomogeneous charge distributions. v2 for M=Pt did not show a peak splitting, while C=C bands for the deuterium analogue exhibited a behaviour similar to those for M=Ni.

We present the low-temperature crystal structures of (BDTFP) 2 PF 6 and (BDTFP) 2 AsF 6 below the phase transition temperatures ( T p ). In the former compound, the c -axis is doubled and thus the dimerized structure changed into a tetramerized structure. At the same time, a new charge-transfer (CT) transition appears at 7000–8000 cm −1 . These two findings are consistent with the non-magnetic state below T p . In the latter, on the other hand, the dimerized structure is maintained below T p , and instead AsF 6 ion rotates along with the ca. 10° rotation of BDTFP. This structural change is the origin of the first-order phase transition to a paramagnetic state.

An anthracene-linked bisphenalenyl Kekule molecule with very significant singlet biradical character has shown a prominent covalent bonding interaction between molecules in a molecular aggregate. High aromatic stabilization energy in the anthracene linker is responsible for the significant singlet biradical character.

A novel naphthoquinoid singlet biradical (2a) stabilized by phenalenyl rings is prepared by a multistep procedure and is investigated in terms of covalent bonding interactions. The molecule 2a gives single crystals, in which a 1D chain is formed with a very short π-π contact at the overlapping phenalenyl rings. The unpaired electrons in 2a are involved in covalent bonding interactions not only within the molecule but also between the molecules in the 1D chain, and a linear conjugation is made of the alternating intra- and intermolecular covalent bonding interactions through conventional π-conjugation and multicenter bonding, respectively. The linear conjugation causes a lower-energy shift of the optical transition band in the crystal, but the transition energy is higher than that of the benzoquinoid singlet biradical (1a). This optical behavior and the magnetic susceptibility measurements reveal that the intermolecular covalent bonding interaction in the 1D chain of 2a is greater in strength than the intramolecular one, despite the fact that a fully conjugated Kekulé structure can be drawn for 2a.

The accurate degree of charge transfer (CT) of BO complexes was obtained by Raman spectroscopy. A rich variety of states with partial CT in a wide range were available for BO materials, either due to stoichiometry or incomplete CT. Above certain acceptor strength, in the complex with BO there is a tendency for the acceptor to be ionized to the fully ionic state of −1 regardless the redox potential in general. The transport properties of BO complexes were discussed in terms of CT degree.

International audience; We have examined the temperature dependence of optical reflectance spectra of (EDO-TTF)2SbF6 salt, and succeeded to detect the thermal hysteresis by the reflectance spectra. In order to investigate high pressure effects on the metal-insulator transition of SbF6 salt, we have performed Raman experiments under pressures up to 6 kbar. Drastic changes in the frequencies of charge sensitive C=C stretching modes suggested the pressure-induced reentrant metal-insulator-metal transition at room temperature.