Conductive Radical Cation Salts Research Articles

MT-pyrene-Based Conductive Radical Cation Salts: Crystal and Electronic Structure and Transport Properties

MT-pyrene-Based Conductive Radical Cation Salts: Crystal and Electronic Structure and Transport Properties

Conservation of structural arrangements and 3 : 1 stoichiometry in a series of crystalline conductors of TMTTF, TMTSF, BEDT-TTF, and chiral DM-EDT-TTF with the oxo-bis[pentafluorotantalate(v)] dianion.

The occurrence of isostructural conducting radical cation salts of diversely substituted tetrathiafulvalene (TTF) precursors with the same anion is most often limited to very similar derivatives such as tetramethyl-tetrathiafulvalene (TMTTF) and tetramethyl-tetraselenafulvalene (TMTSF). Here we show that the use of the oxo-bis[pentafluorotantalate(v)] dianion [Ta2F10O]2− affords upon electrocrystallization of TMTTF, TMTSF, bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF), racemic dimethyl-ethylenedithio-tetrathiafulvalene ((rac)-DM-EDT-TTF), and enantiopure (S,S)-DM-EDT-TTF a series of mixed valence crystalline radical cation salts with the same 3 : 1 stoichiometry. The donor layers show similar features in the five materials, such as alternation of trimeric units within stacks which arrange in parallel columns of β-type. The anion arranges either parallel or perpendicular to the stack direction and establishes numerous intermolecular CH⋯F hydrogen bonds. Thus, the [Ta2F10O]2− dianion, most likely because of its shape and propensity to engage in hydrogen bonding, is the first one to be able to induce the same type of structural arrangement for a broad series of different donors, a result which is important in the crystal engineering of molecular conductors. All the compounds are band gap semiconductors, according to single crystal resistivity measurements and extended Hückel band structure calculations. The room temperature conductivity values are relatively high, i.e. 0.25–1.1 S cm−1, except for the TMTTF salt, whose conductivity value is two orders of magnitude smaller than its isostructural TMTSF counterpart, in agreement with the band gap energy value. As a general feature of these materials, variations in the inter- and intra-trimer interactions modulate their band structure, i.e. energy dispersion and band gaps. The preparation of this series of radical cation salts with a sturdy 3 : 1 stoichiometry might question previous assignments of the anion as [Ta2F11]− in radical cation salts of TMTSF and BEDT-TTF.

New low-dimensional molecular conductors based on bis(ethylenedithio)tetrathiafulvalene radical cation salts with octahedral metal complex anion [ReIVCl6]2–

Three new radical cation salts of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) with the magnetic metal complex anion [ReIVCl6]2–, viz., β-(BEDT-TTF)2[ReCl6] (1), α´-(BEDT TTF)4[ReCl6]•(DCE)2 (2), and δ-(BEDT-TTF)4[ReCl6]1.33•(CB)0.67 (3) (DCE is dichloroethane, CB is chlorobenzene), were synthesized for the first time. The X-ray diffraction analyses of the obtained crystals at room and low temperatures showed that all of them had the sandwich structure characteristic of alternating anionic and cationic layers, which is characteristic of conducting radical cation salts. The structural phase transition accompanied by unit cell tripling and decreasing the symmetry from monoclinic to triclinic in the low-temperature phase occurs in the crystals of salt 2. The transition is related to modulated displacements of both [ReIVCl6]2– anions and BEDT-TTF radical cations. A specific feature of the crystals of salt 3 is a strong positional disorder in the anionic layer, which is expressed as a random distribution of [ReIVCl6]2– anions and CB solvent molecules in a ratio of 2 : 1 along the channels in the ordered cationic framework.

Molecular conductors with differently oriented conducting layers, (EDT-TTF)3Hg2Br6 and (TMBEDT-TTF)5Hg(SCN)4-xIx

New conducting radical cation salts (EDT-TTF)3Hg 2Br6, (TMET) 5Hg(SCN) 4-xIx (x≈0.35), and (EDT-TTF)3Hg(SCN)3I0.5(PhCl)0.5 were synthesized. Their conductivities, ESR and polarized reflectance spectra were studied. It was shown that the organic conductors with differently oriented conducting layers (EDT-TTF)3Hg2Br6 and (TMET)5Hg(SCN)4-xIx (x≈?0.35) are characterized by the quasi-one-dimensional character of electron motion. The conductivity along and across conducting layers has a semiconductive character. It was established by ESR and polarized reflectance spectroscopy that the properties of such conductors are a superposition of the properties of individual conducting layers.

New molecular conductors with cobalt bis(dicarbollide) anion

At present only a few conducting radical cation salts containing metallacarborane anions were described [1-3]. It should be noted that no salts derived from the cobalt bis(dicarbollide) anion [3,3’-Co(1,2-C2B9H11)2] , the most studied metallacarborane [4], were reported. Here new electroconducting salts of cobalt bis(dicarbollide) anion: (TMTSF)2[Co(C2B9H11)2] (1), (TTF)[Co(C2B9H11)2] (2) and (ET)[Co(C2B9H11)2] (3) were synthesized and investigated. The conductivity of crystals (1) at room temperature is 15 Ohmcm, which is the maximal value for metallacarborane salts. The comparison of the crystal structures of salts (1) and (2) showed, that the substitution of more prolate and volumetric TMTSF cation by a less prolate and volumetric TTF cation results in dramatic structural changes which allow us to explain the decrease of conductivity in (2) in comparison to (1) at 9 orders. Mainly it can be connected with the presence of conducting stacks of TMTSF cations in (1), while in (2) there are no stacks but pairs formed by TTF cations. This work was supported by Russian Foundation for Basic Research (grants Nos. 04-03-97203, 05-03-32987).

Synthesis and Properties of Ethylenethiotetra- selenafulvalene (ET-TSF) and Its Conductive Radical Cation Salts

The title heterocycle-fused tetraselenafulvalene derivative, ET-TSF (ethylenethiotetraselenafulvalene) has been synthesized as a novel electron donor. Electrocrystallization of ET-TSF gave highly conductive radical cation salts with I 3 - , Cl - , Br - , and AuI 2 - counter anions. Among them, the AuI 2 salt isostructural with the organic superconductor (MDT-TSF)-AuI 2 (MDT-TSF = methylenedithiotetraselenafulvalene) was highly conductive (1600 S cm -1 ) and metallic down to 1.8 K with no superconducting transition.

Synthesis and properties of conductive radical cation salts of MDT-TSF (methylenedithiotetraselenafulvalene)

Electrocrystallizaion of MDT-TSF (methylenedithiotetraselenafulvalene) in the presence of ( n-Bu 4N)AuI 2, ( n-Bu 4N)PF 6, or a mixture of Cu(SCN), KSCN, and 18-crown-6-ether as a supporting electrolyte gave (MDT-TSF)-X salts (X=AuI 2, PF 6, or Cu(NCS) 2). X-ray structural analyses revealed that the salts adopt various types of crystal structures depending on the counter anion involved; the AuI 2 salt takes a characteristic uniform stacking structure, the PF 6 salt θ-type, and the Cu(NCS) 2 salt κ-type structure. Regardless of the structure type, all the salts are highly conductive at room temperature (>10 2 S cm −1) and retain metallic down to low temperature. Of them, the AuI 2 salt having a high conductivity of 2000 S cm −1 at room temperature showed a superconducting transition at 4.5 K.

Novel Conductive Radical Cation Salts Based on Methylenediselenotetraselenafulvalene (MDSe-TSF): A Sign of Superconductivity in κ-(MDSe-TSF) 2Br Below 4 K

Seven conductive radical cation salts based on MDSe-TSF (methylenediselenotetraselenafulvalene) have been synthesized by electrocrystallization in the presence of Cl −, Br −, I 3 −, I 2Br −, PF 6 −, ClO 4 −, and Cu(NCS) 2 − counter anions. The crystal appearances of these salts fairly depend on the anions employed. X-ray crystallographic analyses have revealed that the PF 6 and ClO 4 salts in the shape of brown thin plates adopt the θ-type structures characterized by the herringbone arrangement of donor stacks, whereas the Cl and Br salts in the shape of black thick plates favor the κ-type structures with the orthogonal arrangement of donor dimers. Regardless of different crystal appearances or crystal packing patterns, all these salts show high conductivity (>10 2 S cm −1) at room temperature and retain metallic properties down to 4.2 K. Of them, the Br salt shows a weak but distinct diamagnetic shielding signal below 4 K in the dc magnetization measurement under zero-field-cooled (ZFC) condition, suggesting a sign of superconductivity. The band calculations of both PF 6 and Br salts demonstrate closed Fermi surfaces indicative of two-dimensional molecular conductors.

Synthesis and properties of novel unsymmetrical tetraselenafulvalene donors, EDT-PT-TSF and EDT-PS-TSF

In order to develop novel electron donors, by structural modification to a superior electron donor, bis(ethylenedithio)-tetraselenafulvalene (BETS 2 ), unsymmetrical TSF derivatives ethylenedithio-propylenethio-TSF (EDT-PT-TSF 5 ) and ethylenedithio-propyleneseleno-TSF (EDT-PS-TSF 6 ) have been effectively synthesized. The synthetic method involves a one-pot formation of 1,3-diselenole-2-selones from acetylene derivatives, a cross-coupling to the TSF system, and finally a ring construction of the outer heterocycles. Electrocrystallization of 5 affords a series of conductive radical cation salts with BF 4 − , PF 6 − , AsF 6 − , ClO 4 − , and SbF 6 − anions, which are of the 2:1 or 3:2 composition ratio. All of the salts with 2:1 ratio are stable metals down to 4.2 K without any specific phase transitions. X-ray crystallographic analyses confirm that they have so-called κ-type donor arrangements.

ChemInform Abstract: Improved Synthesis of Double‐Bridged Tetraselenafulvalenophanes and Formation of Their Conductive Radical Cation Salts.

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Improved Synthesis of Double‐Bridged Tetraselenafulvalenophanes and Formation of Their Conductive Radical Cation Salts

Improved Synthesis of Double‐Bridged Tetraselenafulvalenophanes and Formation of Their Conductive Radical Cation Salts

Improved Synthesis of Double-Bridged Tetraselenafulvalenophanes and Formation of Their Conductive Radical Cation Salts

Improved Synthesis of Double-Bridged Tetraselenafulvalenophanes and Formation of Their Conductive Radical Cation Salts

Synthesis, Structures, and Properties of a Series of Double-Bridged Tetrathiafulvalenophanes as Novel Electron Donors for Conductive Radical Cation Salts

A series of double-bridged tetrathiafulvalenophanes (TTF phanes) with different alkylenedithio (methylenedithio, ethylenedithio, trimethylenedithio, and tetramethylenedithio) bridges was synthesized as a model of interactive dimeric TTFs. They were found to exist as a mixture of three stereoisomers of cis/cis, cis/trans, and trans/trans (twist) types, which were separated by fractional crystallization, and the unique stacking structures of the three isomers were elucidated by X-ray crystallographic analyses and NMR spectroscopy. Their cyclic voltammograms demonstrated multi-redox waves split by intramolecular through-space electronic interactions depending on the bridge lengths. The principal redox-active species was estimated to be of the trans/trans (eclipse) type in the low oxidation states, which was not detected in the neutral state, and to be of the cis/cis type in the high oxidation states. Electrocrystallization gave various radical cation salts, which were mostly semiconductive and characterized ...

Developments of Peri-Dichalcogen-Bridged Fused Aromatic Hydrocarbons as Novel Electron Donors Forming Conductive Molecular Complexes

The developments of novel non-TTF type electron donors forming conductive molecular complexes are presented, especially focussing on methyl-substituted tetrachalcogeno-naphthalenes, anthracenes, and tetracenes. These compounds have been designed chiefly to possess advantageous characteristics, such as strong donating ability, enhanced solubility, and marked heteroatomic interaction, all of which are essential to electron donors forming organic metals. As a result, they formed a large number of conductive molecular complexes and radical cation salts. In particular, the NO3− , BF4− , and Cl− salts of the dimethyl tetraselenoanthracene showed high room temperature conductivities of 440, 450, and 700 Scm−1, respectively, with metallic behavior. Furthermore, the Br− salt of the dimethyl tetratelluroanthracene showed an extraordinarily high conductivity of 1300 Scm−1.

Bis(phenylenedithlo)tetrathiafulvalene (BPhDT-TTF): Synthesis and properties of a new π-donor for organic metals

The new π-donor bis(phenylenedithio)tetrathiafulvalene ( 7), synthesized via phosphite coupling of 2-oxo-1,3-dithiolo[4,5 b][1,4]benzodithiin ( 6) has been prepared in five steps starting from dimercaptobenzene ( 1) and chloroactyl chloride ( 2). Spectroscopic and electrochemical data of 7 are presented. Electrocrystallization yielded highly conducting radical cation salts ( σ RT = 100 S/cm) as fibers (typical dimensions: 10000x 50x20μm). Structural aspects, obtained on these salts by microdifraction techniques, will be discussed.

Conductive Radical Cation Salts with Organic Anions of {RO-C[C(CN)2]2}

Abstract 2-alkyloxy substituted tetracyanoallyl anions (RO-TCA−, R = Me, Et, Pr, Bu) were examined in the formation of the radical cation salts of organic donor molecules systematically. 14 kinds of salts have been obtained so far. Among them, (BEDO-TTF)2(EtO-TCA)(H2O)0.75 showed weak metallic temperature dependence of the conductivity down to ca. 180 K ([sgrave]rt = 30 S cm−1). The crystal structure analyses of (BEDT-TTF)2(PrO-TCA) (needle form) and (TTT)(MeO-TCA) revealed the layered structure in both cases. The two C(CN)2 groups in an anion are twisted to each other in either salts. The structures of the anion layers showed the existence of various packing patterns for this anion series.

Organic–inorganic molecular aggregates and their association within long-range ordered crystalline assemblies: relevance to the template effect in solid-state chemistry

A series of conducting radical cation salts of 1,2-bis(4,5-dimethyltetrathiafulvalen-4′-yl)ethane [bis(DMTTF)ethane], a bifunctional donor with two quasi-degenerate redox functionalities, has been prepared by electrocrystallization; two kinds of binary radical cation salts, [bis(DMTTF)ethane]3[Re6Q6Cl8], Q = Se, 1; S, 2 and [bis(DMTTF)ethane]2[Re6Q5Cl9], Q = Se, 3; S, 4 and a ternary phase [bis(DMTTF)ethane]5[Re6Se6Cl8][Re6Se5Cl9], 5, have been obtained. All five compounds present the same one-dimensional (1D) structural organization in which a stack of donor molecules is surrounded by cluster anions. The degree of oligomerization of the radical cation moieties within the stack is shown to be controlled solely by the cluster anion charge. Thus, the long-range ordered merging of 1 and 3 has led to the formation of the molecular alloy 5. The electronic properties of 1–5 deduced from the band structure calculations and the magnetic properties observed by single-crystal EPR are analysed in relation with the structural changes and the spin distribution on the TTF moieties. The role of the organic chalcogen-inorganic chalcogen interactions is also discussed. In particular, the spin-Peieris transition observed in 1 and absent in 2 is shown to be associated with significant donor-anion interactions only present in 1. Finally, the relation between the degree of purity of 1 and the absence of a pseudo-gap in the spin-Peieris transition is demonstrated.

New conducting radical cation salts based on BEDTTTF and tetracyanometallates square planar dianions [M(CN)42−, M=Pt(II), Ni(II)

The BEDTTTF salts based on tetracyanometallate dianions exhibit a rich polymorphism giving rise to semiconductor, metallic and even superconductor materials. New (BEDTTTF)4M(CN)4(H2O)x (M=Ni, Pt; x= 0→4) phases were prepared. The stoichiometries have been determined by X ray analysis and agree well with the TGA (theromo-gravimetric analysis) results. These salts are isostructural and show a conductor-insulator transition at low temperature. A single crystal structure on the Ni (x=4) salt has been carried out. Crystals belong to the monoclinic space group P2/c with a=17.403(4), b=6.767(9), 15.030(3), β=109.26(2), R=0.05 for 2795 reflexions. The ESR line width dependence on temperature revealed a phase transition at about 180K. These phases are highly localised and present good candidates for a low temperature Peierls transition.

The Crystal Structure of [(Pyrene•−){Na+[(C2H5)2O]}]: A Model for Stacked Radical Anion Salts

A polymeric contact cation pair with a zigzag arrangement of the π electron system is revealed for the stacked structure of the title compound in the solid state (the diagram left depicts a “monomer”). Although this structure allows a comparison with electrically conducting radical cation salts, strong coulombic forces would impair charge transport.

Ring-strain-modified properties of substituted perylene radical cation salts. A solid-state carbon-13 CPMAS NMR study

The authors have considered the stereochemical distortions of the molecular building blocks as a way to control the structure to properties relationships of organic conductive solids. 1,2,7,8-Tetrahydrodicyclopenta (cd,lm)perylene (CPP) and 3,4,9,10-tetramethylperylene (TMP), bearing sterically hindered substituents that involve strain-induced distortions of the perylene skeleton, have been synthesized. Two conductive radical-cation salts, CPP{sub 2}PF{sub 6}{center dot}CH{sub 2}Cl{sub 2} and TMP{sub 2}PF{sub 6}{center dot}CH{sub 2}Cl{sub 2}, have been prepared from these two strained donors by galvanostatic electrocrystallizations at {minus}20C in CH{sub 2}Cl{sub 2}. These two salts are isostructural (monoclinic, space group C{sub 2/m}). The structures consist of similar regular stacks of the almost planar donors (the bond lengths and angle values being distorted as expected) along the crystallographic c axis. The refinements of the structures have been difficult because of the disorder of the counterions and of the solvent contained in the channels between the organic stacks. Solid-state {sup 13}C CPMAS NMR, has been used to study both salts. They exhibit two different locally resolved {sup 13}C conduction electron Knight shift sets.