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Crystal engineering principles serve as a guide for the design of quantum materials based on hydrogen-bond donor/acceptor-functionalized $\pi $-donors of C1symmetry as illustrated by $\delta $–(EDT-TTF-CONMe$_{2})_{2}$AsF6, a non-dimerized, 1/4-filled band Mott insulator and (EDT-TTF-CONH$_{2})_{6}$[ Re6Se8(CN)6] , a metallic molecular Kagomé ($\rm S = 1/2$)where molecular movements are coupled to a Mott localization.

The radical cation salts based on BDH-TTP and the mono- and diamide functionalized derivatives of EDT-TTF with the double charged nitroprusside anion [ FeNO(CN)5] 2- (NP): $\kappa $-(BDH-TTP)4[NP]C6H5NO2(1), $\kappa $-(BDH-TTP)4[NP] (2), (BDH-TTP)2[NP] (3), α-[ EDT-TTF-CONH2] 4[NP] (4), $\beta $-[ EDT-TTF-(CONH$_{2})_{2}$] 2[NP]0.5(C6H5NO$_{2})_{0.5}$(5) have been synthesized. The crystal structures and transport properties of 1 –5, as well as electronic band structures of 1and2have been studied. Key words.organic conductors based on radical cation salts – X-ray and band structure – conductivity.

We present an NMR analysis (spectra and relaxation data) of 77Se nuclei for (TMTSF)2ReO4, (TMDTDSF)2ReO4and (TMDTDSF)2PF6. In all compounds the temperature dependence of the relaxation enhancement (TT1)-1follows the square of the temperature dependent uniform static susceptibility χsin the paramagnetic regime. Deviations from this behaviour are visible in (TMDTDSF)2PF6below the charge localization temperature Tρand are explained in terms of antiferromagnetic correlations. the staggered susceptibility follows a square root temperature divergence in the vicinity of the phase transition towards a spin density wave state. The scaling theory for the quasi-one-dimensional electron gas model accounts very well for the NMR behaviour of these mixed molecule systems. Although the electron charge density on Se sites determined using an extended Hückel type calculation suggests a non negligible influence of disorder on the 77Se Knight shifts, the results cannot account in a satisfactory way for the observed shape of the 77Se spectra.

We have performed the simultaneous investigation of the isotope effect on the superconducting transition and on the Raman spectra in the organic superconductor βH-(BEDT-TTF)2I3(Tc= 8 K). For this purpose, we substitute 13C for 12C on the carbon sites of the central double bond of BEDT-TTF molecule. The isotope shifts measured by Raman experiments can be fairly well explained by standard molecular dynamics. However, the critical temperature is lowered by 0.2 K in the 13C enriched material. We analyse the possible sources of this remarkable downward shift which leads to an isotope coefficient higher than the BCS value. The extended-Hückel calculations of the density of states for the two HOMO bands of βH-(BEDT-TTF)2I3do show that, within the framework of a weak coupling theory, its sizeable variation on the scale of ωDcannot account for the observed isotope effect. On the other hand, we discuss how inelastic electronic scattering observed in resistivity measurements just above Tccan lead through a pair breaking mechanism to a sizeable increase of the isotope coefficient.

We report magnetotransport measurements in the quasi one dimensional (Q-1-D) organic conductor (TMTTF)2Br at pressures up to 26 kbar, clown to 0.45 K in magnetic fields up to 19 T along the c*direction. It is found that a superconducting ground state is stabilized under 26 kbar at TC= 0.8 K. No magnetic field induced spin density wave (FISDW) transitions are observed below 19T unlike other Q-1-D superconductors pertaining to the selenium series. The computed amplitude of the interchain coupling along transverse directions is unable to explain the missing; FISDW instability.

Magnetotransport measurements have been carried out in layered organic metal α-(ET)2TlHg(SeCN)4at temperatures down to 0.4 K and under hydrostatic pressure. Only one...

The synthesis, crystal and electronic band structures as well as conducting properties of the new stable molecular metal [ Pd(dddt)2] Ag1.54Br3.50(dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolato) are reported. the crystal structure contains layers of donor cations alternating with layers of silver bromide complex anions along the aaxis of the unit cell. The Ag and Br atoms are disordered in the anion layer. The conducting layers contain uniform stacks of the translationally equivalent Pd(dddt)2cations along the c-axis with a Pd...Pd distance of 4.157(2) Å. Within the cation layers there are shortened interstack S...S contacts (3.49(3) and 3.56(3) Å). The temperature dependence of the resistivity exhibits metallic behaviour down to 1.3 K. The resistivity anisotropy ($\rho_a^*/\rho_{bc}$) at room temperature is about 600 and does not change considerably when decreasing the temperature down to 4.2 K. The origin of the metallic conductivity of [ Pd(dddt)2] Ag1.54Br3.50as well as the stability of this salt with respect to metal-to-insulator transitions is explained on the basis of tight binding band structure calculations.

The synthesis, crystal structure, conductivity and electronic band structure of the new molecular metal α-(BEDT-TTF)2TlHg (Se$_{1-x}$SxCN)4($x=0.125$) are reported. α-(BEDT-TTF)2TlHg(Se$_1-x$SxCN)4($x=0.125$) is isostructural with all other members of the family of α-(BEDT-TTF)2MHg(XCN)4salts and is a stable metal down to very low temperatures. A general study of the electronic structure of all structurally characterized α-(BEDT-TTF)2MHg(XCN)4salts as well as α-(BEDT-TTF)2I3, α-(BEDT-TTF)2IBr2and α-(BEDT-TTF)4PtBr6is also reported. Different aspects related to the electronic structure of these salts like the stability of the metallic state and the nature of the Fermi surface are discussed and correlated with the details of their crystal structures. The origin of the different dimensionality of the carriers for the α-(BEDT-TTF)2MHg(XCN)4salts (i.e., 1D electrons but 2D holes), the metal to insulator transition in α-(BEDT-TTF)2I3and the semiconducting behavior of α-(BEDT-TTF)2IBr2and α-(BEDT-TTF)4PtBr6are also discussed.

We report the synthesis by confined electrocrystallization and the characterization of the transport properties of the monoclinic polymorphs of the Bechgaard-Fabre salts μ’-(TMTTF)2ReO4, μ’-(TMTTF)2IO4 and μ”-(TMTSF)2ClO4.

Abstract: We report the synthesis by confined electrocrystallization and the characterization of the transport properties of the monoclinic polymorphs of the Bechgaard-Fabre salts μ′-(TMTTF)2ReO4, μ′-(TMTTF)2IO4 and μ′-(TMTSF)2ClO4.

Two new organic conductors based on BEDT-TTF radical cation salts with the [FeNO(CN)5]2−anion have been synthesized. β″-(BEDT-TTF)2[FeNO(CN)5] (1) and β″-(BEDT-TTF)3[FeNO(CN)5]·EG (2) have been characterized by single-crystal X-ray diffraction, electrical resistance measurements, and electronic band-structure calculations. A detailed comparison of 1and 2with β″-(BEDT-TTF)4A[FeNO(CN)5]2(3) is reported. 2and 3are organic metals stable down to low temperatures while 1is a semiconductor. Analysis of the correlation between the crystal and electronic structures as well as the transport properties of these molecular conductors suggests the possibility of changing their physical properties through chemical control of the composition of the anionic layers.

Crystal engineering principles serve as a guide for the design of quantum materials based on hydrogen-bond donor/acceptor-functionalized ?-donors of C1 symmetry as illustrated by ??(EDT-TTF-CONMe2)2AsF6, a non-dimerized, 1/4-filled band Mott insulator and (EDT-TTF-CONH2)6[ Re6PF8(CN)6] , a metallic molecular Kagom? (S = 1/2)where molecular movements are coupled to a Mott localization.

The structure of hydrogen molybdenum bronze phase III, HxMoO3 (x ≈ ⁵/3) has been studied on the basis of a combined experimental−theoretical approach. Our study of the average structure allows us to qualify previous contradictory results concerning the octahedral distortions and show no sign of hydrogen occupation of the intralayer sites. A first-principles theoretical study of this average structure leads to a clear understanding of the nature of the band structure as well as the importance and requirements for metal−metal bonding. The nature of the calculated Fermi surface suggests that a 3b × 2c superstructure may be a better description for phase III, which would be compatible with powder X-ray diffraction (XRD) results. Since the information available from powder XRD data does not allow a direct determination of the superstructure, the problem has been approached by means of first-principles geometry optimizations and molecular dynamics studies. The main structural features of this superstructure (distribution of Mo−Mo bonds, main distortions of the Mo−O network and hydrogen distribution) are described.

Three new 2,5‐bis(1,3‐dithiolan‐2‐ylidene)‐1,3,4,6‐tetrathiapentalene (BDH‐TTP) radical cation salts with the photochromic nitroprusside anion have been synthesized: κ‐(BDH‐TTP)4[FeNO(CN)5]·NB (1), κ‐(BDH‐TTP)4[FeNO(CN)5] (2), and (BDH‐TTP)2[FeNO(CN)5] (3). The salts were characterized by single‐crystal X‐ray diffraction, electrical resistance measurements, and electronic band structure calculations. The crystals of 1and 2have a layered structure in which the BDH‐TTP layers of κ‐type alternate with anionic sheets. Solvent (nitrobenzene) molecules are also involved in the composition of the anion sheet of 1. The crystals of 1have triclinic symmetry and two crystallographically independent BDH‐TTP radical cations in the unit cell, while there is only one independent radical cation in the monoclinic structure of 2. The salts 1and 2are stable quasi‐2D metals down to 4.2 K, while 3, with full charge transfer, is a semiconductor with low conductivity at room temperature. It is suggested that the κ‐type layers of BDH‐TTP are more robust than those of BEDT‐TTF and its derivatives and the consequences for the electronic structure are discussed.

A qualitative scheme that leads to the step-by-step construction of the band structure and Fermi surface of molecular conductors is developed based on a simple analytical treatment as well as some fundamental symmetry and overlap ideas and the concept of folding. This treatment is valuable in that it provides a detailed understanding of how the crystal and electronic structures of molecular conductors are related. Specifically, the proposed perspective clarifies how relatively weak structural changes can result in significant differences in the transport properties of these materials. Molecular conductors with donor layers of the β"-type are used in order to illustrate the approach.

A qualitative scheme that leads to the step‐by‐step construction of the band structure and Fermi surface of molecular conductors is developed based on a simple analytical treatment as well as some fundamental symmetryand overlapideas and the concept of folding. This treatment is valuable in that it provides a detailed understanding of how the crystal and electronic structures of molecular conductors are related. Specifically, the proposed perspective clarifies how relatively weak structural changes can result in significant differences in the transport properties of these materials. Molecular conductors with donor layers of the β″‐type are used in order to illustrate the approach.

Four (BEDT‐TTF)4A[M(C2O4)3]·DMF (DMF = dimethylformamide) salts of the organic donor molecule bis(ethylenedithio)tetrathiafulvalene (BEDT‐TTF) with metal oxalate anions, where A = (NH4, K), M = Cr (1); A = NH4, M = Fe (2); A = K, M = Cr (3); and A = NH4, M = Cr (3′) were prepared by electrocrystallization. These salts were characterized by single‐crystal X‐ray diffraction, electron spin resonance (ESR) spectroscopy, electrical resistance measurements, and electronic band structure calculations. The structures (with space group C2/c) consist of alternating β″‐type layers of BEDT‐TTF and an approximately hexagonal network formed by the A+cation and the metal, with the solvent molecule, DMF, occupying hexagonal cavities in the anion layer. All of the salts are two‐dimensional organic metals down to 4.2 K and do not exhibit superconductivity. Their electronic band structure is similar to that of the known organic superconductor β″‐(BEDT‐TTF)4H3O[Fe(C2O4)3]·BN. The ESR spectra of salts 1and 3′ are characterized by two resonances, one of Gaussian shape arising from the 3d localized electrons of Cr3+and the other of Lorentzian (and Dysonian) shape due to the conduction electrons in the organic layers. On the basis of the calculated Fermi surfaces it is suggested that these salts could exhibit an interesting magnetoresistance behavior if disorder does not prevent the observation of the Shubnikov‐de Haas oscillations.

In this paper we review some recent results on the electronic structure of III–VI layered semiconductors and its dependence under pressure, stressing the specific features that differentiate their behaviour from that of tetrahedrally coordinated semiconductors. We will focus on several unexpected results that have led to changes in the image that was currently accepted a few years ago. Intralayer bond angles change under pressure and the layer “thickness” remains virtually constant or increases. As a consequence, models based in intra- and inter-layer deformation potentials fail in explaining the low pressure nonlinearity of the band gap. Numerical-atomic-orbital/density-functional-theory electronic structure calculations allow for an interpretation of the evolution of the absorption edge under pressure. In particular, they show how the structure of the non-degenerated valence band maximum in InSe becomes more complex under pressure leading to a non-conventional direct-to-indirect crossover. The valence band maximum in InSe above 4 GPa exhibits a quite singular feature: a “ring-shaped” constant energy surface and, consequently, a density of states depending on energy as in 2D electronic systems.

Electrooxidation of the nickel dithiolene complex [Ni(F2pdt)2]–·(F2pdt2‐: 6,6‐difluoro‐6,7‐dihydro‐5H‐[1,4]dithiepine‐2,3‐dithiolato) affords the corresponding neutral complex [Ni(F2pdt)2]0whose layered structure is highly reminiscent, albeit not isostructural, of that of the isosteric fluorinated bis(propylenedithio)tetrathiafulvalene and characterized by a segregation of the fluorinated moieties into fluorous bilayers. The gold neutral complex [Au(F2pdt)2]·, which is isostructural with the fluorinated bis(propylenedithio)tetrathiafulvalene, was prepared by electrocrystallization of the [n‐Bu4N][Au(F2pdt)2] salt. [Au(F2‐pdt)2]·is a semiconductor with high room temperature conductivity. The origin of this semiconducting behavior as well as possible guidelines in order to realize metallic conductivity in gold dithiolene neutral molecular solids are discussed.

Abstract:: This article reports the investigation of a new low-dimensional organic salt, (TTDM-TTF)2 [Au(mnt)2], by single crystal X-ray diffraction, static magnetic susceptibility, EPR, thermopower, electrical resistivity measurements under pressure up to 25 kbar and band structure calculations. The crystal structure consists in a dimerized head to tail stacking of TTDM-TTF molecules separated by layers of orthogonal Au(mnt)2 anions. The absence of overlap between neighboring chains coming from this particular crystal structure leads to an extreme one-dimensionality (1-D) for which the carriers of the half-filled conduction band become strongly localized in a Mott-Hubbard insulating state. This material is the first 1-D conductor in which the Mott-Hubbard insulating character cannot be suppressed under pressure.

Electrocrystallization of the novel π-electron donor (ethylenethio)(ethylenedithio)tetrathiafulvalene (ETEDT-TTF) with trihalide anions has given rise to a new family of radical cation salts with insulating properties, [ETEDT-TTF]X, and conducting properties, ETEDT-TTF]X0.42, where X = I3^- or IyBr3-y^-. According to X-ray data, in the isostructural completely ionic [ETEDT-TTF]X salts, the donor radical cations are strongly dimerized, with an interplane distance of 3.310−3.317 Å, and the mixed-valence [ETEDT-TTF](I3)0.42 salt is formed by segregated radical cation and anion layers alternating along the b axis. The latter salt exhibits semiconductor behavior with a high room-temperature conductivity of 24 S·cm^-1. The large angle between the molecular planes of the donors in neighboring stacks precludes the possible metallic behavior of this salt. Interestingly, nanocrystals of the mixed-valence salts are the conducting component of new bilayer (BL) composite films that have been generated via the ETEDT-TTF + I2 and ETEDT-TTF + IBr chemical reactions. The structure and composition of the conducting layers of these new BL films were confirmed by X-ray, EPR, and Raman spectroscopies. Similarly to the single crystals, these composite materials exhibit semiconducting behavior with a room-temperature conductivity ranging from 0.25 to 2.5 S·cm^-1. SEM and NIR studies of the film samples were also carried out.

A new organic semiconductor with trinitroresor-cinol as the anion, (TMTTF)2(C6H2N3O8) (1) (TMTTF: tetramethyltetrathiafulvalene),

The synthesis and X-ray crystal structure of the ethane-linked dimeric tetrathiafulvalene [(EDT-TTF−CH2)2], 1,2-bis(ethylenedithiotetrathiafulvalenyl)ethane (1), is reported. It oxidizes reversibly at 0.45 and 0.90 V vs SCE. Electrocrystallization in the presence of [n-Bu4N][FeCl4] or [n-Bu4N][GaCl4] affords isostructural, mixed-valence conducting 1:1 salts [1^•+][FeCl4^-][THF]0.5 and [1^•+][GaCl4^-][THF]0.5 whose X-ray crystal structures are described. The intercalation of the tetrahedral anions within the organic slabs and the resulting sliding of the molecular diads on top of each other give rise to both 1D- and 2D-type HOMO···HOMO interactions whose origin is correlated with the details of the peculiar overlap patterns obtained with those dimeric tetrathiafulvalenes. The weak paramagnetism observed in the GaCl4^- salt due to the organic spins of the conducting slabs is hidden in the FeCl4^- salt by the S = 5/2 Fe(III) contribution. The absence of sizable magnetic interactions between the organic and FeCl4^- sublattices is accompanied by weak antiferromagnetic FeCl4^-/FeCl4^- interactions, attributable to a short Cl···Cl interanion distance at 3.419(17) Å.

Electrocrystallization of 1,1,2-trichloroethane solutions of the redox-active secondary amide, 3-methylamido-3‘,4‘-ethylenedithiotetrathiafulvalene (EDT-TTF-CONHMe 1) in the presence of n-Bu4NF supported on silica gel afforded a mixed-valence chloride salt, formulated (1)2[Cl·H2O] from elemental analysis and X-ray crystal structure resolution. The chloride anion and water molecule are disordered on the same site, and coordinated to the π-donor molecule by two strong hydrogen bonds involving the amidic N−H and the aromatic C−H group ortho to the amide, thereby qualifying a robust pair of tweezers-like cyclic motif. This efficient anion recognition effect is also observed in solution, as demonstrated by ¹H NMR downfield shifts of both the N−H and C−H hydrogen atom resonances, as well as by a cathodic shift of the oxidation potential of 1 upon Cl^- complexation, establishing that the actual electrocrystallized species is a solvated anionic chloride complex [(1·Cl^-)(H2O)n] rather than the free amide. (1)2[Cl·H2O] adopts a layered β‘ ‘-type structure with segregation of the hydrophobic (EDT-TTF) and hydrophilic (amide, Cl^-, H2O) fragments. The HOMO−HOMO intermolecular interaction energies for the donor layers are large and the Fermi surface exhibits a pronounced two-dimensional character. The EPR Dysonian line observed below 120 K indicates an highly conducting system, confirmed by high room-temperature conductivity of 120 S cm^-1 and metallic behavior down to 0.47 K, with a 167-fold increase of the conductivity, but no indication however of a transition to a superconducting state, a likely consequence of the Cl^-/H2O disorder.

The effect of the first-order phase transition occurring around 220K on the crystal and electronic structure of the molecular superconductor (BEDO-TTF)"2ReO"4.H"2O has been studied. The crystal structure at 170K has been determined and it is found that the main structural change resulting from the phase transition is connected with a rotation of the ReO"4^- anions. This rotation leads to changes in the S...S and S...O intermolecular contacts within the BEDO-TTF donor layers, nevertheless the band structure is remained practically unchanged. Possible changes in the crystal structure which can occur at room temperature depending on the experimental conditions are considered. It seems very likely that the (BEDO-TTF)"2ReO"4.H"2O crystal loses its water molecules in the vacuum and hence changes its crystal structure.

The family of charge transfer salts (DT-TTF)nM(mnt)2, with M=Au, Ni, Pt, Fe and Co, shows a wide range of interesting electrical and magnetic properties. Salts with M=Au, Ni and Pt, with n=2 are isostructural. The Au compound, is a semiconductor and presents a localised regime of charge carriers in DT-TTF chains, behaving as a spin-ladder system. The Ni and Pt analogues have a delocalised regime with higher conductivity at room temperature and a transition to an insulator state at 120 and 127 K respectively. The Fe and Co compounds form ionic salts with n=1 and present poorer semiconducting properties. For M=Fe, crystals of different morphologies and the observation of three different transport properties denote the existence of different phases.

The crystal structures and physical properties of the BEDT-TTF, BEDO-TTF and BBDT-TTF chlorides are discussed. Most of the discussion concerns two hydrated BEDO-TTF chlorides which are stable organic metals down to 1.3 K but have different types of conducting layers and different counter-ions networks.

The family of charge transfer salts (DT-TTF)nM(mnt)2, with M=Au, Ni, Pt, Fe and Co, shows a wide range of interesting electrical and magnetic properties. Salts with M=Au, Ni and Pt, with n=2 are isostructural. The Au compound, is a semiconductor and presents a localised regime of charge carriers in DT-TTF chains, behaving as a spin-ladder system. The Ni and Pt analogues have a delocalised regime with higher conductivity at room temperature and a transition to an insulator state at 120 and 127 K respectively. The Fe and Co compounds form ionic salts with n=1 and present poorer semiconducting properties. For M=Fe, crystals of different morphologies and the observation of three different transport properties denote the existence of different phases.

The crystal structures and physical properties of the BEDT-TTF, BEDO-TTF and BBDT-TTF chlorides are discussed. Most of the discussion concerns two hydrated BEDO-TTF chlorides which are stable organic metals down to 1.3 K but have different types of conducting layers and different counter-ions networks.

We present an NMR analysis (spectra and relaxation data) of 77Se nuclei for (TMTSF)2ReO4, (TMDTDSF)2ReO4and (TMDTDSF)2PF6. In all compounds the temperature dependence of the relaxation enhancement (TT1)-1follows the square of the temperature dependent uniform static susceptibility ?sin the paramagnetic regime. Deviations from this behaviour are visible in (TMDTDSF)2PF6below the charge localization temperature T?and are explained in terms of antiferromagnetic correlations. the staggered susceptibility follows a square root temperature divergence in the vicinity of the phase transition towards a spin density wave state. The scaling theory for the quasi-one-dimensional electron gas model accounts very well for the NMR behaviour of these mixed molecule systems. Although the electron charge density on Se sites determined using an extended H?ckel type calculation suggests a non negligible influence of disorder on the 77Se Knight shifts, the results cannot account in a satisfactory way for the observed shape of the 77Se spectra. Nous pr?sentons une ?tude RMN (spectres et mesures du temps de relaxation T1) sur le noyau 77Se, pour les compos?s (TMTSF)2ReO4, (TMDTDSF)2ReO4et (TMDTDSF)2PF6. Pour tous ces compos?s, la d?pendence en temp?rature du facteur d'augmentation de la relaxation (TT1)-1suit le carr? de la susceptibilit? statique uniforme ?s(T) dans le r?gime paramagn?tique. Des ?carts ? cette variation sont observ?s pour (TMDTDSF)2PF6en dessous de la temp?rature de localisation T?qui sont expliqu?s en thermes de corr?lations antiferromagn?tiques. La susceptibilit? montre une divergence en racine carr?e de la temp?rature au voisinage de transition de phase vers un ?tat onde de densit? de spin. La th?orie d'?chelle pour le mod?le de gaz d'electrons quasi-unidimensionnels d?crit parfaitement le comportement RMN de ces syst?mes organiques mixtes soufre-s?l?nium. Bien que la densit? de charge ?lectronique sur les sites de s?l?nium d?termin?e par un calcul de type H?ckel ?tendu sugg?re une influence non n?gligeable du d?sordre, les r?sultats ne permettent pas de d?crire de fa?on satisfaisante la forme des spectres observ?s pour le noyau 77Se.

Magnetotransport measurements have been carried out in layered organic metal ?-(ET)2TlHg(SeCN)4at temperatures down to 0.4?K and under hydrostatic pressure. Only one... Des mesures de magn?tor?sistance ont ?t? effectu?es dans le conducteur organique bidimensionnel ?-(ET)2TlHg(SeCN)4jusqu'? la temp?rature de 0.4?K et sous pression hydrostatique. Une seule s?rie d'oscillations Shubnikov-de Haas est observ?e dans la gamme de pression comprise entre 3.5 et 11?kbar. La masse cyclotron d?croit lentement lorsque la pression augmente et la fr?quence des oscillations augmente rapidement depuis la valeur de (653?3)T ? pression ambiante jusqu'? (790?3)T ? 11?kbar. Une mod?lisation bas?e sur la m?thode des liaisons fortes sugg?re que la d?pendance en pression de l'aire de l'orbite ferm?e de la surface de Fermi est due au glissement, induit par la pression, des mol?cules des chaines ne contenant qu'un type de donneurs. Au contraire de son compos? fr?re ?-(ET)2NH4Hg(SCN)4, il pr?sente des oscillations lentes, de fr?quence (47?3)T, ? pression ambiante. Elles ne sont pas observ?es entre 3.5 et 11?kbar et pourraient ?tre en relation avec un embo?tement des orbites ouvertes ? pression ambiante qui pourraient d?truire la supraconductivit? dans le compos? ? base de s?l?nium.

We report magnetotransport measurements in the quasi one dimensional (Q-1-D) organic conductor (TMTTF)2Br at pressures up to 26?kbar, clown to 0.45?K in magnetic fields up to 19?T along the c*direction. It is found that a superconducting ground state is stabilized under 26?kbar at TC= 0.8?K. No magnetic field induced spin density wave (FISDW) transitions are observed below 19T unlike other Q-1-D superconductors pertaining to the selenium series. The computed amplitude of the interchain coupling along transverse directions is unable to explain the missing; FISDW instability.

Tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ) form a charge-transfer complex which exhibits a high electric conductivity. In this work TTF-TCNQ thin films were prepared by CVD (chemical vapour deposition) at low pressure and using TTF and TCNQ as precursors. Substrates were common glass. These layers exhibit preferential orientation in the crystallization along the [001] direction and have a room temperature conductivity ranged between 6–24 Ω−1cm−1. Whereas at low temperatures (smaller than a transition temperature Tp) they display a highly resistive semiconductor-like behaviour, above Tpthe conductivity exhibits a small effective activation energy. Tp≈ 50–60 K is interpreted as a signature of the Peierls transition. The evaluation of the stoichiometry was performed by UV-visible spectroscopy. The morphology and structure of the layers were also studied.

Single crystals of a new ternary thiophosphate, KNiPS4, have been synthesized by reaction of the elements in an evacuated silica tube at 873 K for two weeks. The structure was solved in the tetragonal space group P42/mnmwith a= 8.2538(4) Å, c= 10.7553(6) Å, and Z= 4. The refinements led to R= 0.0250 (Rw= 0.0190) for 425 independent reflections and 26 variables. The structure of KNiPS4consists of nickel in square planar sulfur coordination linked by edge-sharing PS4tetrahedral groups to produce one-dimensional chains. The chains are aligned in a parallel manner to form layers perpendicular to the c-axis and they are separated by layers of potassium. Tight-binding band structure calculations suggest that the nickel atoms should be in a low-spin Ni11state resulting in an overall charge balance of KINiIIPV(S-II)4. UV-visible spectroscopic measurements indicate KNiPS4to be semiconducting.

Abstract:: The -(BETS)2C(CN)3 radical cation salt was prepared by electrocrystallization, and its crystal structure was determined by single crystal X-ray diffraction. The electronic structure of -(BETS)2C(CN)3 was studied by means of the extended Hückel tight binding method. The electrical conductivity of this salt as a function of temperature shows a metallic behaviour down to 1.3 K. Shubnikov-de Haas oscillations reveal both the classical and magnetic breakdown orbits on the Fermi surface typical of the -type organic conductors. In addition, a low frequency oscillation (250 T) which is not predicted by the band structure calculations has been found in the oscillation spectrum.

Abstract:: The effect of the first-order phase transition occurring around 220 K on the crystal and electronic structure of the molecular superconductor (BEDO-TTF)2ReO4 · H2O has been studied. The crystal structure at 170 K has been determined and it is found that the main structural change resulting from the phase transition is connected with a rotation of the ReO4‒ anions. This rotation leads to changes in the S···S and S···O intermolecular contacts within the BEDO-TTF donor layers. How these structural changes affect the electronic structure of the salt is studied by comparing the transfer integrals for the different donor···donor intermolecular interactions calculated for the room temperature and 170 K crystal structures. It is shown that Fermi surfaces for the 170 K and room temperature structures are very similar, do not exhibit nesting properties, and can be described as resulting from the hybridization of superposing ellipses.

Low-dimensional metals exhibit a wealth of interesting phenomena associated with the special topology of their Fermi surfaces. These Fermi surfaces contain a very rich information concerning not only the dimensionality of the conductivity but also the possibility of different metal-to-insulator or metal-to-metal transitions. Because the shape of the Fermi surface is to a great extent imposed by the crystal structure, it is important to develop conceptual models to find the link between the crystal structure and the Fermi surface of these systems. An approach based on simple ideas of overlap, symmetry, and chemical bonding is used to analyze some puzzling observations concerning a number of low-dimensional metals including oxides, bronzes, and molecular metals.

Structural studies of some molecular conductors and superconductors D(M(dmit)2)2(D=TTF,Cs,NMe4; M=Ni,Pd) are presented and related to the calculated band electronic structure of these compounds. The charge density wave (CDW) instabilities observed in TTF(M(dmit)2)2(M=Ni,Pd) as well as the low temperature incommensurate phase stabilized in Cs(Pd(dmit)2)2are well accounted for by the properties of their computed Fermi surfaces. We emphasize that the originality of these compounds mainly stems from the weak energy difference between the HOMO (highest occupied molecular orbital) and the LUMO (lowest unoccupied molecular orbital) of the organometallic M(dmit)2molecule.

The title compound contains the discrete, monovalent anion Ta2F11−as evidenced by resolution of the crystal structure: triclinic P1, a=7.798(2), b=10.976(4), c=13.557(4) Åα=90.71(3), ß=99.47(2), γ=102.37(3) °, V=1116.5 Å3, Z=1, R=0.059, Rω=0.070, esd=1.850based on 1851 reflexions and 250 parameters. The stack is strongly trimerized and short inter-stacks contacts confer a significant 2D character to the material as substaintiated by EHT-type tight-binding band structure calculations.

The highly extended sulfur-rich title compounds behave as exceptionaly strong τ-donors, as determined by cyclic voltammetry. A 2-dimensional cation-radical salt, involving an unprecendented type of crystallographic network has been obtained upon electrooxidation.

Single crystals of the charge-transfer complex (BTDM-TTF)-TCNQ, showing metallic character down to 26K, have been obtained. The X-Ray structure reveals segregated stacks of donors and acceptors in a very similar packing with the related HMTSF-TCNQ complex. Electronic structure calculations using a tight-binding model indicate that (BTDM-TTF)-TCNQ is an almost pure ID metal. The electronic and magnetic properties are in accordance with its electronic and structural characteristics. This complex shows the lowest transition temperature reported up to date for charge transfer complexes of TTF derivatives.

We have investigated the resistive superconducting transition of βH-(ET)2I3crystals in which the two inner carbon atoms, in the center of the ET molecule, have been substituted with 13C isotopes. We stabilised the βHstate of (ET)2I3at low temperature via the appropriate cooling procedure in a He gas pressure apparatus (“Orsay process”). The superconducting transition of 13C substituted samples was found to be Tc= 7.80±0.05 K (at midpoint), namely 0.20K lower than that of standard 12C samples (Tc= 8.0±0.1 K). We have taken care that both types of samples were measured in the same conditions and that p(T) data were free from cracks which can broaden the superconducting transition. This large and regular isotope shift of Tcis in contrast with most of the previous results in organic superconductors and suggests the existence of a superconductivity mechanism mediated by the coupling of electrons with the intramolecular phonom models.

The synthesis, crystal and electronic band structures as well as conducting properties of the new stable molecular metal [ Pd(dddt)2] Ag1.54Br3.50(dddt?=?5,6-dihydro-1,4-dithiin-2,3-dithiolato) are reported. the crystal structure contains layers of donor cations alternating with layers of silver bromide complex anions along the a axis of the unit cell. The Ag and Br atoms are disordered in the anion layer. The conducting layers contain uniform stacks of the translationally equivalent Pd(dddt)2cations along the c-axis with a Pd...Pd distance of 4.157(2) ?. Within the cation layers there are shortened interstack S...S contacts (3.49(3) and 3.56(3) ?). The temperature dependence of the resistivity exhibits metallic behaviour down to 1.3?K. The resistivity anisotropy (?a*/?bc) at room temperature is about 600 and does not change considerably when decreasing the temperature down to 4.2?K. The origin of the metallic conductivity of [ Pd(dddt)2] Ag1.54Br3.50as well as the stability of this salt with respect to metal-to-insulator transitions is explained on the basis of tight binding band structure calculations.