Br Salt Research Articles

Electron Localization Induced by Disordered Anions in an Organic Conductor.

We report on a new organic conductor κ″-(ET)2Cu[N(CN)2]Br (κ″-Br), which is the first polymorph of an organic superconductor κ-(ET)2Cu[N(CN)2]Br (κ-Br), where ET denotes bis(ethylenedithio)tetrathiafulvalene. κ″-Br has a similar κ-type arrangement of ET molecules to κ-Br, but, in contrast to the orthorhombic κ-Br, which has ordered polyanion chains, presents a monoclinic crystal structure with disordered polymeric anion chains. To elucidate the electronic state of κ″-Br, we performed band calculations as well as transport, magnetic, and optical measurements. The calculated band dispersion, magnitude of electron correlation, and room-temperature optical conductivity spectra of κ″-Br were comparable to those of κ-Br. Despite these similarities, the κ″-Br salt exhibited a semiconducting behavior. The electron spin resonance and Raman spectroscopies indicated that there is neither magnetic nor charge order in κ″-Br, suggesting the occurrence of Anderson localization due to disordered anion layers.

[DABCO-C18]Br: A novel basic surfactant for the synthesis of dihydropyrano[3,2-c]chromenes and 2-aminobenzochromenes under ambient conditions

We successfully produced a new surfactant called [DABCO-C18]Br, which is a monoquaternized octadecyl-1,4-diazabicyclo[2.2.2]octane bromide. The yield was good. The surfactant that was created was analyzed using techniques such as 1H NMR, 13CNMR, and Mass characterization. We analyzed the synthesized [DABCO-C18]Br salt and found that it has great surfactant properties. Its critical micelle concentration (CMC) is 1.15 mM as determined by the conductivity method and 1.0 mM by UV–Vis absorption measurement at 298.15 K. The values align well with the critical micelle concentration (CMC) of the commonly used surfactant [C16TAB]. We have studied the catalytic efficiency of [DABCO-C18]Br, a tertiary base surfactant, for the synthesis of dihydropyrano[3,2-c]chromenes. This synthesis is achieved through one-pot three-component reactions involving aromatic aldehydes, malononitrile, and 4-hydroxycoumarin in water at room temperature. The method was also extended for the synthesis of 2-aminobenzochromenes via one-pot three-component reactions of aromatic aldehydes, malononitrile, and lawsone in water at 80 °C. The products were achieved in yields ranging from good to excellent within a timeframe of 30–60 min. In addition, the aqueous solution with [DABCO-C18]Br was reused up to four times with a minor reduction in product output. This protocol is fast, energy-efficient, and can be used on a large scale for synthetic purposes. Additionally, it boasts impressive environmentally-friendly credentials.

Exploring properties of potassium 6-X-2-isonicotinoyltrifluoroborate (X=H, F, Cl, Br) salts and their anions by using ab initio calculations.

The structural, electronic, and topological properties of a series of four members of potassium 6-X-2-isonicotinoyltrifluoroborate (X=H, F, Cl, Br) salts have been explored by using ab initio calculations with the hybrid B3LYP/6-311++G** method. According to the potential energy surface only the properties for the most stable conformer of each member of the series and their anions were analyzed in function of electronegativity and atomic radius of X. The results show that when X=H, the salt and its anion have symmetry CS while the symmetry change to C1 for the halogenated F, Cl, and Br derivatives and their anions. Both, electronegativity and atomic radius properties show higher effects on V than on μ. Similar behaviors are observed when the Mulliken charges on N and X atoms are analyzed vs electronegativites, and atomic radius of X while an important decreasing on NPA charges of X is observed when increase its electronegativity. The strong influence of electronegativity and atomic radius of X are evidenced in the low bond order value observed in the C1 atom of F salt. The strong energetic π*C2-C3 → π*C4-C5 transition observed only for the F salt confer to it a high stability. The frontier orbitals have revealed that the 6-H-IFTB salt is the less reactive species while the higher reactivity is predicted for the Br salt. Evidently, the smaller electronegativity and higher atomic radius of Br justify the high reactivity predicted for its salt. Graphical abstractExploring properties of potasium 6-X-2-isonicotinoyltrifluoroborate (X= H, F, Cl, Br).

Crystal structures and properties of radical salts of a new series of tetrathiafulvalene derivatives incorporating fused ethyleneoxymethylene and ethylenethiomethylene units

Tetrathiafulvalene (TTF) derivatives have been widely investigated as functional molecular materials with conducting properties. Radical salts of tetrathiafulvalene (TTF) derivatives incorporating fused ethyleneoxymethylene (EOM) and ethylenethiomethylene (ETM) units were prepared by electrochemical oxidation. Crystal structures of some salts were determined by X-ray structure analyses. The AuI2 salt of bis(ethyleneoxymethylene)-TTF (BEOM-TTF) (1) exhibits a metal-to-semiconductor (MS) transition at 295 K with a high room-temperature conductivity (σRT) of 25 S cm–1 as determined by a two-probe method. Bis(ethylenethiomethylene)-TTF (BETM-TTF) (2) salts with 1:1 stoichiometry are insulators. The Br salt of 4,5-ethyleneoxymethylene-4′,5′-ethylenedithio-TTF (EOMEDT-TTF) (3) exhibits a MS transition at 297 K with a high σRT of 11 S cm–1. 32X salts (X = ClO4–, PF6–) have columnar structures and form head-to-tail dimers with O⋯H short contacts of the EOM groups. The ReO4 salt of 4,5-ethyleneoxymethylene-4′,5′-methylenedithio-TTF (EOMMDT-TTF) (4) exhibits a MS transition at 297 K with σRT of 4.2 S cm–1 and a small activation energy of 0.023 eV below 297 K, and adopts κ-type packing. The salts of ethyleneoxymethylene-TTF (EOM-TTF) (5) and ethylenethiomethylene-TTF (ETM-TTF) (6) donors exhibit semiconductive behaviors. The salt of 53(ClO4)2 has three crystallographically independent molecules and adopts head-to-head stacking with S⋯S and O⋯H short contacts in the triad. By comparing the intramolecular bond lengths of the molecules and splitting of the Raman bands, it was found that the 53(ClO4)2 salt is in a charge order state. Incorporation of the EOM and ETM functional substituents on the TTF skeleton gives rise to many intermolecular interactions between donors in their salts.

Tunneling Spectroscopy in Organic Superconductor κ-(BEDT-TTF-d[3,3])2Cu[N(CN)2]Br

We performed tunneling spectroscopy (STS) measurement in an organic superconductor, partially deuterated κ-(BEDT-TTF-d[3,3])2Cu[N(CN)2]Br. We carried out angle-resolved STS on cut lateral surfaces by the focused ion beam (FIB) method as well as as-grown single-crystal surfaces. It was found that the d[3,3]-Br salt is a strong-coupling d-wave superconductor and that the nodal direction is at an angle of π/4 from the a*-axis, corresponding to the \(d_{x^{2} - y^{2}}\) symmetry in the bulk superconducting phase. It is understood that the electron correlation in the d[3,3]-Br salt is not strong enough on the basis of the spin fluctuation mechanism. On the other hand, we also observed two types of superconducting gap. This suggests the coexistence of the \(d_{x^{2} - y^{2}}\) and dxy symmetries. This indicates a change in the symmetry from \(d_{x^{2} - y^{2}}\) in the bulk superconducting phase to dxy around the insulating region with increasing electron correlation.

Microscopic observation of superconducting fluctuations inκ-(BEDT-TTF)2Cu[N(CN)2]Br byC13NMR spectroscopy

We performed $^{13}$C-NMR experiment and measured spin-lattice relaxation rate divided by temperature $1/T_{1}T$ near the superconducting (SC) transition temperature $T_{c}$ in $\kappa$-(BEDT-TTF)$_{2}$Cu[N(CN)$_{2}$]Br ($\kappa$-Br salt), and $\kappa$-(BEDT-TTF)$_{2}$Cu(NCS)$_{2}$ ($\kappa$-NCS salt). We observed the reduction of $1/T_{1}T$ starting at the temperature higher than $T_c$ in $\kappa$-Br salt. Microscopic observation of quasi-particle density of states in the fluctuating SC state revealed the effects of short-range Cooper pairs induced in the normal state to the quasi-particle density of states. We also performed systematic measurements in the fields both parallel and perpendicular to the conduction plane in $\kappa$-Br and $\kappa$-NCS salts, and confirmed that the reduction of $1/T_{1}T$ above $T_{c}$ is observed only in $\kappa$-Br salt regardless of the external field orientation.

Femtosecond Carrier Relaxation Dynamics and Photoinduced Phase Separation inκ−(BEDT−TTF)2Cu[N(CN)2]X(X=Br,Cl)

We investigate the relaxation dynamics of nonequilibrium carriers in organic conductors κ-(BEDT-TTF)(2)Cu[N(CN)(2)]X (X=Br and Cl) using ultrafast time-resolved optical spectroscopy. The dynamics for both salts show similar temperature dependences, which is well characterized by the carrier relaxation across the pseudogap (PG) of the magnitude Δ(PG) ≈ 16 meV for Br salt and 7.0 meV for Cl salt. On the other hand, only the Br salt shows an abrupt increase of the decay time at low temperature, indicating an additional decay component associated with the superconducting (SC) gap below T(c). The fluence dependent dynamics at low temperature evidences the superposition of the SC component onto the PG component. These results indicate a metallic-insulating phase separation in the Br salt triggered by photoexcited nonequilibrium carriers.

Syntheses, Crystal Structures, Transport Properties and First-Principles Electronic Structure Study of the (tTTF)2X (X = Br, I) Low-Dimensional Antiferromagnets

An efficient synthetic procedure for the preparation of unsymmetrically substituted tetrathiafulvalene (TTF) donors has been used to obtain the trimethylene-tetrathiafulvalene (tTTF) donor with high purity. Good quality crystals of the two (tTTF)(2)X (X = Br, I) salts have been obtained by electrocrystallization. The two salts are isomorphous and contain tTTF layers which are built from (tTTF)(2) dimeric units. Both systems are low-dimensional antiferromagnets with the highest Néel temperatures for TTF based radical cation salts: ≈ 35 K (Br salt) and ≈43 K (I salt). The resistivity is found to substantially decrease with pressure although both salts still have activated conductivity at 25 kbar. First-principles Density Functional Theory (DFT) calculations have been used to investigate the relative strength of the three different types of magnetic interactions in the tTTF layers as well as the potential magnetic ground states. These calculations successfully predict the nature of the ground state and suggest a possible correlation between structural details and Néel temperatures for the bromine and iodine salts. Remarkably, the calculated antiferromagnetic ground state can be predicted from the nesting properties of the Fermi surface for the hypothetical Pauli paramagnetic metallic state.

Structural Distortions upon Oxidation in Heteroleptic [Cp2W(dmit)] Tungsten Dithiolene Complex: Combined Structural, Spectroscopic, and Magnetic Studies

Four different cation radical salts are obtained upon electrocrystallization of [Cp(2)W(dmit)] (dmit = 1,3-dithiole-2-thione-4,5-dithiolato) in the presence of the BF(4)(-), PF(6)(-), Br(-), and [Au(CN)(2)](-) anions. In these formally d(1) cations, the WS(2)C(2) metallacycle is folded along the S···S hinge to different extents in the four salts, an illustration of the noninnocent character of the dithiolate ligand. Structural characteristics and the charge distribution on atoms, for neutral and ionized complexes with various folding angles, were calculated using DFT methods, together with the normal vibrational modes and theoretical Raman spectra. Raman spectra of neutral complex [Cp(2)W(dmit)] and its salts formed with BF(4)(-), AsF(6)(-), PF(6)(-), Br(-), and [Au(CN)(2)](-) anions were measured using the red excitation (λ = 632.8 nm). A correlation between the folding angle of the metallacycle and the Raman spectroscopic properties is analyzed. The bands attributed to the C═C and C-S stretching modes shift toward higher and lower frequencies by about 0.3-0.4 cm(-1) deg(-1), respectively. The solid state structural and magnetic properties of the three salts are analyzed and compared with those of the corresponding molybdenum complexes. Temperature dependence of the magnetic susceptibility shows the presence of one-dimensional antiferromagnetic interactions in the BF(4)(-), PF(6)(-), and [Au(CN)(2)](-) salts, while an antiferromagnetic ground state is identified in the Br(-) salt below T(Néel) = 7 K. Interactions are systematically weaker in the tungsten salts than in the isostructural molybdenum analogs, a consequence of the decreased spin density on the dithiolene ligand in the tungsten complexes.

Synthesis, characterization, and dc conductivity of hydrogen-bonding dibenzotetrathiafulvalene (DBTTF) based salts

The synthesis, characterization, and dc conductivity of organic conductors, 1-[2-(1,3-benzodithiol-2-ylidene)-1,3-benzodithiol-5-yl]ethylammonium tetrafluoroborate ([DBTTFCH(Me)NH 3 +]BF 4 −) and 1-[2-(1,3-benzodithiol-2-ylidene)-1,3-benzodithiol-5-yl]ethylammonium bromide ([DBTTFCH(Me)NH 3 +]Br −) salts are presented. These salts are prepared by mixing the corresponding primary amine and Brønsted acid in a one-to-one ratio without electrochemical oxidation. The change in the electronic state of insulating DBTTFCH(Me)NH 2 into conductive [DBTTFCH(Me)NH 3 +]X − (X = BF 4 and Br) salts and the carrier generation upon salt formation were confirmed by diffuse reflectance (UV–vis) and ESR spectra. The concentration of localized radicals is estimated to be 1 radical/3.3 units and 1 radical/1.8 units for BF 4 and Br salts, respectively. The possible carrier generation mechanism is proposed by 1H NMR and ESI-TOF-MS spectroscopic analyses. The dc conductivity and the activation energy are σ rt = 2.3 × 10 −3 S/cm with 0.24 eV for the BF 4 salt, and σ rt = 1.3 × 10 −3 S/cm with 0.21 eV for the Br salt.

Exploring the charge-ordering transition in [formula omitted] via thermal expansion measurements

We report results of high-resolution measurements of the c * ‐axis expansivity ( α c * ) at the charge-ordering (CO) transition for the quasi-1D (TMTTF) 2 X compounds with X = SbF 6 and Br and make a comparison with previous results for the X = PF 6 and AsF 6 salts. For X = SbF 6 , due to the screening of the long-range Coulomb forces, a sharp λ -type anomaly is observed at T CO , which contrasts with the step-like mean-field anomaly at T CO for PF 6 and AsF 6 , where CO occurs in the Mott–Hubbard charge-localized regime. For the latter two salts, a negative contribution to α c * is observed above T CO . This feature is assigned to the anions’ rigid-unit modes, which become inactive for T < T CO . Our α c * results for the X = Br salt, where such rigid-unit modes are absent, reveal no traces of such negative contribution, confirming the model based on the anions’ rigid-unit modes for the X = PF 6 and AsF 6 salts.

Anomalous Temperature Dependence ofg-Tensor in Organic Conductor, (TMTTF)2X (X=Br, PF6, and SbF6)

The magnetic properties of organic conductor (TMTTF) 2 X (X=Br, PF 6 , and SbF 6 ), where TMTTF is tetramethyltetrathiafulvalene, were examined by electron spin resonance (ESR) spectroscopy, X-ray diffraction (XRD) of the single crystals, and quantum–chemical calculation of the g -tensor. In the case of salts with bulky counter anions such as the PF 6 and SbF 6 , an anomalous temperature dependence of the g -tensor was observed in the temperature range from 20 to 296 K. This anomalous behavior of the g -tensor signifies the rotation of the principal axes as well as the shift of the principal values. The g -tensor of the Br salt is, however, temperature independent. No remarkable change in the intra-molecular structure as a function of temperature was observed for all salts. On the other hand, the distance between TMTTF and counter-anion molecules obviously decreases as the temperature decreases for the PF 6 and SbF 6 salts, while thermal contraction is not remarkable for the Br salt. In order to clarify the origin of the anomalous behavior of the g -tensor, we investigated the possibility of deformation of the wave-function by the counter-anion potentials using a quantum–chemical calculation for the actual crystal structures measured at low-temperatures. In this paper, we describe the first direct observation of the deformation of the frontier orbital by the counter anion potential for organic conductors. The intra-molecular spin-distribution as a function of temperature is also discussed from the microscopic point of view.

Strong Rail Spin 1/2 Antiferromagnetic Ladder Systems: (Dimethylammonium)(3,5-Dimethylpyridinium)CuX4, X = Cl, Br

The mixed cation salts, (dimethylammonium)(3,5-dimethylpyridinium)CuX4 (X = Cl, Br), henceforth (DMA)(35DMP)CuX4, are new examples of spin-ladders based on nonbonded halide...halide interactions between CuX4(2-) anions. In these structures, double rows of the CuX4(2-) anions are sheathed by the 35DMP(+) cations, while the edges are capped by the DMA(+) cations. For the Br salt, the Br...Br contacts that define the rungs of the ladder are 4.017 A in length, while those that define the rails are 3.983 A. For the Cl salt, the corresponding lengths are 3.967 and 4.045 A. The susceptibility data for the Br salt exhibits a maximum at approximately 5.5 K, and fitting the data to the spin 1/2 antiferromagnetic ladder model yields 2J(rail)/k = -7.95 K and 2J(rung)/k = -4.07 K. The exchange coupling is much weaker in the Cl salt, no maximum in chi is observed down to 1.8 K, and the corresponding exchange constants are -1.59 and -1.25 K, respectively. An analysis is made of the structural factors involved in the J(rung) pathway.

Calorimetric study of molecular superconductor κ-(BEDT-TTF)2Ag(CN)2H2O which contains water in the anion layers

Thermodynamic investigation of an organic superconductor κ-(BEDT-TTF)2Ag(CN)2H2O in which the BEDT-TTF dimers are arranged in the κ-type structure in the donor layers is performed by the relaxation calorimetric technique at low temperatures and under magnetic fields. A thermal anomaly related to the superconductive phase transition was observed at 5 K. The existence of residual γ* in the superconductive state is about 18% of the normal state γ value, which is larger than those of κ-(BEDT-TTF)2Cu(NCS)2, and κ-(BEDT-TTF)2Cu[N(CN)2]Br salt. The lattice heat capacity reflected on the β-term in the low-temperature heat capacity was found to be affected by the cooling rate. The disorder produced in the network structure constructed by hydrogen bond in the insulating layer is considered to give low-energy phonon excitations reflected in the heat capacity.

Lattice effects and entropy change at the Mott transition of a quasi-2D organic conductor

Layered organic charge-transfer salts of the κ - ( BEDT - TTF ) 2 X family have emerged as exemplary systems for exploring effects of strong electron–electron correlations. Here we report on high-resolution dilatometric investigations on a fully deuterated crystal of the X = Cu [ N ( CN ) 2 ] Br salt, where the Mott metal–insulator (MI) transition—a key phenomenon of strongly correlated electron systems—can be explored through temperature sweeps. Measurements of the uniaxial expansivities reveal discontinuous lattice changes at T MI ≃ 14 K , accompanied by a striking in-plane anisotropy. The entropy change at T MI , determined from the volume change, is small, indicating that T MI coincides with the Néel-temperature T N at this point in the phase diagram.

Homogeneous/heterogeneous palladium based catalytic system for Heck reaction. The reversible transfer of palladium between solution and support

Pd(II)/Al2O3 and Pd(0)/Al2O3, containing 0.6% of palladium were characterized by EDX, SEM and XRD methods and used as catalysts of the Heck coupling of bromobenzene with butyl acrylate at 140 °C in molten [Bu4N]Br salt. Monoarylated (trans-PhCH = CHC(O)OBu) (1) and diarylated (Ph2C = CHC(O)OBu) (2) products were obtained in amounts dependent on kind of base present in the system (Scheme 1). During the reaction palladium was partially leached from the support forming [Bu4N][PdBr4] complex that catalyze Heck reaction or undergo readsorption on Al2O3. These soluble palladium complexes are partially reduced to Pd soluble nanoparticles which can also be anchored on Al2O3 giving active catalyst of Pd(0)/Al2O3 type. Reduction of Pd(II) to Pd(0) during catalytic process at the presence of bases (NaHCO2, NaHCO3, NaOAc, Cs2CO3) was studied by XPS method and the total reduction was observed in reactions of PdCl2(PhCN)2 with NaHCO2 or with NaHCO3 and [Bu4N]Br. It was experimentally proved that heterogenized catalyst, Pd(0)/Al2O3, after oxidative addition of aryl halides, serve as a source of soluble palladium species and colloidal nanoparticles that are active as homogeneous catalysts.

Phase separation behaviour on κ-(BEDT-TTF)2Cu[N(CN)2]Br

The system of the deuterated κ-(BEDT-TTF-d[n,n]) 2 Cu[N(CN) 2 ]Br is situated in the critical region between the superconducting(SC) phase and the antiferromagnetic insulator (AFI) phase, and is just on the Mott type critical boundary of paramagnetic metal (PM) phase and paramagnetic insulator (PI) phase. We perform two single-crystal 13 C-NMR studies on the non and the fully deuterated κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br at low temperature with the applied field 9.4T. We found two new experimental results. One is that the phase separation is found in κ-(BEDT-TTF-d[0,0]) 2 Cu[N(CN) 2 ]Br salt, like partially deuterated κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br salt. The other is that the phase separation is observed at around T* with the applied field parallel to the conducting layer, unlike partially deuterated κ-(BEDT-TTF-d[n,n]) 2 Cu[N(CN) 2 ]Br. The former result suggests the field induces AF transition. the latter result suggests there is the field direction dependence of the M-I phase separation behavior in κ -(BEDT-TTF-d[4,4]) 2 Cu[N(CN) 2 ]Br.

Cooling rate dependence of the in-plane magnetic penetration depth in κ-type BEDT-TTF superconductors

We performed dc magnetization measurements under the control of cooling-rate in the organic superconductors κ-(BEDT-TTF) 2 X (X=Cu(NCS) 2 and Cu[N(CN) 2 ]Br). A distinct different cooling-rate dependence of the in-plane magnetic penetration depth (λ // (0)) was observed between two salts, where λ // (0) was estimated from a linear extrapolation to 0 K. In the Cu(NCS)2 salt, λ // (0) remains unchanged regardless of cooling-rate, while T c decreases slightly in faster-cooling. On the other hand, λ // (0) in the Cu[N(CN) 2 ]Br salt becomes long significantly in faster-cooling. We quantitatively explain the change of λ // (0) in the cooling-rate as an impurity effect by terminal ethylene disorder in BEDT-TTF molecules in terms of the local and clean limit approximation.

Structures and physical properties of cation radical salts based on low-symmetrical ethylenedioxy-ethylenedithio-TTF

Crystal structures and physical properties have been investigated for two cation radical salts formed with EOET, which is a hybrid molecule between ET and BO. The Mott-insulating κ'-(EOET) 2 Cu[N(CN) 2 ]Br salt has a spin-singlet ground state, while the κ-(EOET) 2 GaCl 4 salt with a triangular lattice composed of EOET dimers shows a metal-insulator transition at around 40 K.

Field-induced superconductor–insulator transition in layered organics

A partially deuterated κ-(BEDT-TTF)2Cu[N(CN)2]Br salt, which is a superconductor situated near the Mott insulator, has been investigated by resistivity measurements under magnetic fields. The superconducting transition of this salt is replaced by the first-order metal–insulator transition by magnetic field. This field-induced transition fades away when the sample cooling around 80 K is slowed down. The present findings lead us to bring to mind possible realization of the ideal electric switch controllable with the magnetic field.