Spectroscopic investigations of the BEDT-TTF charge transfer salts with NO3− anions (β″- and δ-phase)

We report the polarized reflectance spectra (650–6500 cm⁻¹) as well FT-NIR Raman spectra of β″-(BEDT-TTF)₃(NO₃)₂ and δ-(BEDT-TTF)₂(NO₃)_0.9(NO₂)_0.1 salts as a function of temperature. Additionally, the crystal structure of δ-phase salt was determined at room temperature and the temperature dependence of electrical conductivity was measured. The reflectance spectra of metallic β″-phase salt were fitted with the Drude model; the metal–insulator transition at T = 20–27 K has practically no influence on IR spectra. The δ-phase salt shows semiconducting behavior; inside conducting organic layers the BEDT-TTF molecules are arranged in dimers. The specific vibrational features of the δ-salt are discussed in terms of hydrogen bonding between BEDT-TTF and anions.     

EPR study of arene radical cation salt crystals

Single-crystal EPR studies of the charge transfer salts grown by the electrochemical oxidation of p-terphenyl (TP) and p-quaterphenyl (QP) in the presence of PF₆⁻ at −25 °C and +5 °C respectively, are reported. The TP salt exhibits an angular-dependent EPR linewidth varying between 70 and 125 mG at −48 °C and a g tensor of 2.00312, 2.00230 and 2.00206, while the QP salt exhibits an angular-dependent linewidth varying between 150 and 220 mG and a g tensor of 2.00310, 2.00217 and 2.00217, suggesting a pseudo reorientation about the chain axis, a feature not previously detected in other arene salt crystals.     

Low-dimensional magnetic behaviour of new radical-ion salts: (BEDT-TTF)2[AuIII(i-mnt)2] and (BEDT-TTF)2[BiBr4]

Electrical and magnetic properties of two new radicalion salts of BEDT-TTF (BEDT-TTF is bis(ethylenedithio)-tetrathiafulvalene) are reported. (BEDT-TTF)₂[Au^III(i-mnt)₂] (i-mnt is 1,1-dithio-2,2-dicyano-ethylene) is a semiconductor, σ_r.t. = 2.0 × 10⁻¹−5.5 × 10⁻² S cm⁻¹ with a temperature dependent activation energy (0.14–19 eV). The powder magnetic susceptibility (10–300 K) has been fitted according to a uniform antiferromagnetic (S = 1/2) Heisenberg model by using the experimental g value of 2.0067 and a magnetic exchange constant J/k_B of −110 K. (BEDT-TTF)₂ [BiBr₄] shows similar electrical and magnetic behaviour with σ_r.t. = 5 × 10⁻² S cm⁻¹ on a powdered sample and J/k_B = − 79 K. At low temperature impurities are responsible for the Curie-like behaviour.     

Crystal and electronic structures of the radical cation salt based on EDT-TTF and the photochromic nitroprusside anion, (EDT-TTF)3[Fe(CN)5NO]

A single crystal X-ray diffraction (XRD) study of the radical cation salt (EDT-TTF)₃[Fe(CN)₅NO] has been carried out (a=6.623(3), b=10.487(2), c=15.951(1) Å, α=109.19(1), β=96.30(2), γ=99.15(3)°, V=1017.3(5) Å³, space group P1, Z=1). The crystals have a layered structure with the distinctive feature of the presence of alternating EDT-TTF dimers and monomers in the radical cation stacks. Both the structural features and the calculated HOMO⋯HOMO interaction energies suggest that the strong intradimer interaction is responsible for the charge separation and the semiconducting properties of the salt.     

离子交换法制备铂(II)和钯(II)的硝酸四氨络合物及结构表征

采用一种全新的方法—离子交换法,以二氯四氨合铂(II)和二氯四氨合钯(II)为原料,水为溶剂,制备铂、钯的重要催化前驱体化合物—硝酸四氨合铂(II)和硝酸四氨合钯(II)。通过元素分析、红外光谱、质谱、核磁共振表征其化学结构。方法的产率＞90%,产品纯度＞99.0%(以金属铂、钯计),适合于批量生产要求。     

Temperature dependence of the reflectance spectrum of bis-(ethylendithio)tetrathiafulvalenium perchlorate, (BEDT-TTF)3(ClO4)2

The polarized reflectance spectrum of bis(ethylenedithio)tetrathiafulvalenium perchlorate, (BEDT-TTF)₃(ClO₄)₂, was measured in the infrared and visible regions at room temperature, 200 K and 150 K. The anisotropic ratio of the transfer integrals between the directions parallel and perpendicular to the [012] axis was estimated to be 0.59 on the (100) plane. A drastic change of the reflectance spectrum was observed below the phase transition temperature.     

Cis-[Pt(NH_3)_2(H_2O)_2](NO_3)_2与1,1-环丁烷二羧酸钠形成的一种新的Pt(Ⅱ)配合物(英文)

从Cis-[Pt(NH3)2(H2O)2](NO3)2 与1,1-环丁烷二羧酸钠的化学反应中,分离出一种新的Pt(II)配合物,通过元素分析、红外光谱, 质谱和高效液相色谱的分析测试,初步推测结构为顺式-四氨-μ-二(1,1-环丁烷二羧酸根-O1,O2)合二铂的新化学结构式.     

The first BDH-TTP radical cation salts with mercuric counterions, κ-(BDH-TTP)4[Hg(SCN)4]·C6H5NO2 and α′-(BDH-TTP)6[Hg(SCN)3][Hg(SCN)4]

Two new radical cation salts of the non-TTF containing donor BDH-TTP with the thiocyanatomercurate anions were synthesized. The κ-(BDH-TTP)₄[Hg(SCN)₄]·C₆H₅NO₂ (1) and α′-(BDH-TTP)₆[Hg(SCN)₃][Hg(SCN)₄] (2) salts were characterized by single crystal X-ray diffraction, electrical resistance measurements and electronic band structure calculations. Both salts have a layered structure in which the BDH-TTP layers of κ- or α′-type alternate with anionic sheets. The anionic layers of 1 contain the counterion [Hg(SCN)₄]²⁻ and the nitrobenzene molecule which are statistically disordered. Salt 2 contains two different layers (although both of the α′-type) of the organic donors, a somewhat unusual fact in organic conductors. The anion layers of 2 consist of polymeric chains built up from a combination of the two different anions, [Hg(SCN)₃]¹⁻ and [Hg(SCN)₄]²⁻. Salt 1 shows a metallic behavior down to helium temperatures whereas salt 2 exhibits two-phase transitions in the temperature range 295–8 K.     

Fermi surface reconstruction in (BEDT-TTF)2TlHg(SCN)4

The Shubnikov-de Haas (SdH) measurements of the two dimensional organic conductor (BEDT-TTF)₂TlHg(SCN)₄ have been performed to investigate the Fermi surface reconstructed by the spin density wave formation. At 0.05 K, ten different SdH oscillations are found. A model of the reconstructed Fermi surface is proposed on the basis of the relation between the observed SdH frequencies.     

A study of the thermal expansion of isostructural organic radical cation salts κ-(BEDT-TTF)2Cu[N(CN)2]X (X = Br, Cl,I)

High resolution thermal expansion measurements on single crystals of κ-(BEDT-TTF)₂Cu[N(CN)₂]X, with X = Br, Cl, I were performed along the three principal directions in the temperature range from 2 to 300K. The temperature dependence of the linear thermal expansion of the two superconductors (X = Br, Cl) is found to be completely different from that of the non-superconducting I-salt. Cooling the I-crystal, we found an elongation of the c- axis, a larger contraction of the a-axis and a smaller contraction of the b-axis in comparison to the bromide- and the chloride- salt. Common to the three compounds are large anomalies in the linear thermal expansion coefficients _i at a temperature T_d = 84K, 80K, 73K for X = I, Br, Cl, respectively. The magnitude and the sign of these anomalies in _i strongly depend on the anion composition. At T_d the _i's show steplike changes, which lead to a lattice distortion of opposite sign for the superconductors and for the I-salt. These anomalies indicate a second order phase transition at T_d, which eventually may be related to a disorder-order transformation of the terminal ethylene groups of the donor molecules.     

Time scale of electronic and molecular motions in the conducting radical cation salt diperylene hexafluorophosphate

Frequency and temperature dependence of nuclear spin lattice relaxation is used for the derivation of motional time scales in the quasi-one-dimensional conductor diperylene hexafluorophosphate (incorporating tetrahydrofurane (THF) solvent molecules). Freezing in of reorientational motion of the THF molecules at the stack-rotation phase transition T_r ≈ 153 K is proved by the use of perdeuterated solvent. Slowing down of hexafluorophosphate rotational motion is reflected by ¹⁹F and ¹H relaxation in the 100 K range. The time constant describing termination of the diffusive decay of the conduction-electron spin correlation is estimated from frequency-dependent proton spin relaxation including rotating-frame data.     

Spectroscopic studies of the Eu(III) and Gd(III) tris(3-aminopyridine-2-carboxylic acid) complexes

The synthesis and spectroscopic studies of the complexes of Eu(III) and Gd(III) with 3-aminopyridine-2-carboxylic acid (3-NH₂pic) are described. An experimental and theoretical analysis of the intensities of the ⁵D₀→⁷F_0,1,2,4 transitions of the Eu(III) ion is presented. An approximate structure for the Eu(III) complex is assumed and the theoretical calculations are based on a model, previously described, which takes into account the forced electric dipole and dynamic coupling mechanisms.     

Spectroscopic studies of KGd(WO4)2:Ho single crystals

Single crystals of KGd(WO₄)₂ doped with Ho³⁺ ions were grown by the top seeded solution growth method. Polarized room temperature absorption spectra were analyzed by means of the conventional Judd-Ofelt theory taking into account strong dependence of the host refractive index on the wavelength. In addition to the intensity parameters Ω₂, Ω₄, Ω₆, the branching ratios and radiative lifetimes were estimated for all possible transitions in the studied spectral region. The transitions predicted by the phenomenological model as potential transitions for laser applications are discussed. Emission spectra in the green, red, and near-infrared spectral regions were recorded for different excitation wavelengths. Comparison with spectroscopic properties of Ho³⁺ ion in other crystals is discussed.     

Magnetic field studies of the peculiar electronic state in the α-(BEDT-TTF)2MHg(SCN)4 family

Magnetoresistance anomalies exhibited by the members of the α-(BEDT-TTF)₂MHg(SCN)₄ family with M = Tl, K and Rb are reviewed in connection with possible modification of their electronic structure at low temperatures. Special attention is paid to angular magnetoresistance oscillations (AMRO). The analysis of the AMRO behavior at various temperatures and magnetic fields, both below and above the phase transition temperature, enables us to get an important information about changes in the electronic band structure at the phase transition. Other peculiarities of both semi-classical magnetoresistance and quantum oscillations are discussed within the proposed model of the low-temperature state of these compounds.     

Multi-component molecular conductors with supramolecular assembly based on ET radical cation salts with (NO3)− anion

Synthesis, structure and conducting properties of two new multi-component radical cation ET salts with the (NO₃)⁻ counterion: (ET)₂(NO₃)·C₂H₄(OH)₂ (I) and (ET)₂(NO₃)·0.5[C₂H₄(OH)₂]·H₂O (II) are described. Both salts have layered structures with the distinguishing feature of hydrogen bonds being present between the radical cation layers and anion sheets. It was found that introduction of glycol molecules to compositions of I and II significantly affects the structure of their cation and anion layers and, as a result, their conducting properties. I is a semiconductor, while II demonstrates metallic conductivity down to 4.2 K.     

Electrical anisotropy of α-(BEDT-TTF)2KHg(SCN)4

The transverse magnetoresistance of α-(BEDT-TTF)₂KHg(SCN)₄ was investigated with the magnetic field rotated within a conducting ac-plane. It was found that the magnetic-field-orientation dependence of the magnetoresistance in the weak-field limit, ΔR(B,θ), has the form ΔR(B,θ) = B²(psin²(θ − θ_min) + qcos²(θ − θ_min), where θ is the angle betweeen a-axis and magnetic field direction and (p, q, θ_min) are temperature-dependent parameters. By examining the results based on the classical theory of magnetoresistance, it was concluded that the electrical anisotropy within be-plane is 3.5 4.5 and 2.5 3.0 above and below the phase transition at 10 K, respectively.     

Temperature dependence (300 to 10K) of the structural and electronic properties of the molecular charge-transfer salt (BEDT-TTF)3 Cl2,2H2O

The crystal and electronic structure of the molecular charge-transfer salt (BEDT-TTF)₃ Cl₂ 2H₂O was determined at 10, 130, 190 and 295K. The thennal expansion has been evaluated from measurements of cell parameters between 10 and 295K.     

Thin film of bis(ethylenedithio)-tetrathiafulvalene radical salt with Dawson polyoxometalate

The thin film of bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF or ET) radical salt with Dawson polyoxometalate [P₂W₁₈O₆₂]⁶⁻ was prepared on gold substrate by using electrochemical process. The film was characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), electron spin resonance spectroscopy (ESR) and cyclic voltammetry (CV). Scanning electron microscope (SEM) micrograph of the film exhibits a smooth and uniform surface layer containing micronic grains. The thickness of the film estimated by SEM is ca. 22 μm. The film exhibits semiconducting behavior with a room-temperature conductivity 6.5 × 10⁻³ S cm⁻¹.