Search

Tetramethyl-tetraselenafulvalene (TMTSF) and bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF) are flagship precursors in the field of molecular (super)conductors. The electrocrystallization of these donors in the presence of (n-Bu4N)TaF6 or mixtures of (n-Bu4N)TaF6 and (n-Bu4N)PF6 provided Bechgaard salts formulated as (TMTSF)2(TaF6)0.84(PF6)0.16, (TMTSF)2(TaF6)0.56(PF6)0.44, (TMTSF)2(TaF6)0.44(PF6)0.56 and (TMTSF)2(TaF6)0.12(PF6)0.88, together with the monoclinic and orthorhombic phases δm-(BEDT-TTF)2(TaF6)0.94(PF6)0.06 and δo-(BEDT-TTF)2(TaF6)0.43(PF6)0.57, respectively. The use of BEDT-TTF and a mixture of (n-Bu4N)TaF6/TaF5 afforded the 1:1 phase (BEDT-TTF)2(TaF6)2·CH2Cl2. The precise Ta/P ratio in the alloys has been determined by an accurate single crystal X-ray data analysis and was corroborated with solution 19F NMR measurements. In the previously unknown crystalline phase (BEDT-TTF)2(TaF6)2·CH2Cl2 the donors organize in dimers interacting laterally yet no organic-inorganic segregation is observed. Single crystal resistivity measurements on the TMTSF based materials show typical behavior of the Bechgaard phases with room temperature conductivity σ ≈ 100 S/cm and localization below 12 K indicative of a spin density wave transition. The orthorhombic phase δo-(BEDT-TTF)2(TaF6)0.43(PF6)0.57 is semiconducting with the room temperature conductivity estimated to be σ ≈ 0.16–0.5 S/cm while the compound (BEDT-TTF)2(TaF6)2·CH2Cl2 is also a semiconductor, yet with a much lower room temperature conductivity value of 0.001 to 0.0025 S/cm, in agreement with the +1 oxidation state and strong dimerization of the donors. [ABSTRACT FROM AUTHOR]

Using a slow liquid–gas diffusion method, the mixed-valence viologen salt (MV)2(BF4)3 (1) and the radical cation salt (MV)(BF4) (2) are crystallized. Both structures contain regular stacks of MVṖ+ radical cations (2) or alternating MVṖ+ and MV2+ entities (1). A short intrastack intermolecular separation (3.23 Å) unprecedently reveals strong interactions between MV2+ and MVṖ+ in 1. [ABSTRACT FROM AUTHOR]

Electrocrystallization of TMTTF (tetramethyltetrathiafulvalene) in the presence of the dianionic [Pt(qS)2]2− platinum complex (qS: 5-sulfo-8-quinolinol) afforded simultaneously two phases. Phase A with isolated dicationic (TMTTF)22+ species is fully insulating and characterized by C–H hydrogen bonds with the anionic sulfonate moieties. Phase B is a mixed valence salt formulated as (TMTTF)3[Pt(qS)2]. It is organized into strongly trimerized chains, with a notably higher conductivity (σRT = 4 × 10−5 S cm−1). The charge distribution within the TMTTF trimers has been evaluated from the intramolecular bond distances, and IR and Raman spectra, converging all to a +0.5/+1/+0.5 motif, which is not modified at lower temperatures. Spectroscopic studies of such trimeric structures are scarce and the doublet (or triplet) structure expected in the IR of trimers is clearly identified here in the EMV-activated ν8(ag) mode associated with the totally symmetric vibration of methyl groups, in relation to the weak C–H⋯O hydrogen bonds between the radical cation and the dianionic [Pt(qS)2]2− platinum complex. [ABSTRACT FROM AUTHOR]

A series of 2D metals, β-(BDT-UP)6[Re6Se6Cl8]·(CHCl2-CHCl2)2, 2; β-(ST-UP)6[Re6S6Cl8]·(CH2-Cl-CHCl2)2, 3; β-(BDT-UP)7[Re6S6Cl8]0.5[Re6S7Cl7]0.5·(CH2Cl2), 4; β-(BDT-UP)7[Re6Se6Cl8]0.5[Re6S7- Cl7]0.5(CH2Cl2), 5; β-(BDT-UP)8[Re6S7Cl7]·(CH2Cl2)4, 6 (BDT-TTP and ST-UP are 2,5-bis(1,3-dithiol-2- ylidene)-1,3,4,6-tetrathiapentalene and 2-(1,3-diselenol-2-ylidene)-5(1,3-dithiol-2-ylidene)-1,3,4,6-tetrathiapentalene, respectively) is reported to have one single β-slab layered topology despite successive increases of the cluster anion negative charge. The charge density within the templating composite inorganic-neutral molecule slab is shown to remain above a threshold of ca. one negative charge per square nanometer, that is, for cluster anions with two negative charges and higher. Conversely, discrete stacks are shown to be stabilized instead in the semiconducting salts (BDT-TTP)2[Re6S5Cl9], 1 where the cluster anion bears one negative charge only. The electronic structure of salts 2-6 is shown to be very stable and kept almost intact across the series. The templating strategy is shown to fulfill its anticipated potential for deliberate installment of incommensurate band fillings in molecular metals. The deliberate admixture of the 6:1 and 8:1 structures yields novel phases with a 7:1 stoichiometry with the anticipated crystal and electronic structures. The action at the organic-inorganic interface triggered by changing the anion charge yet keeping its shape and volume identical, which ultimately governs the shape of the unit cell, is of paramount importance in defining the Fermi surface of these metallic salts. The present BDT-UP salts thus provide a series of materials with strongly related but subtly different Fermi surfaces worthy of many physical studies. Shubnikov-de Haas measurements are expected to be particularly interesting since they are especially sensitive to the details of the Fermi surface. [ABSTRACT FROM AUTHOR]

(EDT-TTF-CONH2)6[Re6Se8(CN)6], space group R..., was prepared by electrocrystallization from the primary amide-functionalized ethylenedithiotetrathiafulvalene, EDT-TTF-CONH2 (E½1 = 0.49 V vs SCE in CH3CN), and the molecular cluster tetraanion, [Re6Se8(CN)6]4- (E½ = 0.33 V vs SCE in CH3CN), equipped with hydrogen bond donor and hydrogen bond acceptor functionalities, respectively. Its Kagome topology is unprecedented for any TTF-based materials. The metallic state observed at room temperature has a strong two-dimensional character, in coherence with the Kagome lattice symmetry, and the presence of minute amounts of [Re6Se8(CN)6](3-)· identified by electron spin spectroscopy. A structural instability toward a distorted form of the Kagome topology of lesser symmetry is observed at ca. 180 K. The low-temperature structure is associated with a localized, electrically insulating electronic ground state and its magnetic susceptibility accounted for by a model of uniform chains of localized S = ½ spins in agreement with the 100 K triclinic crystal structure and band structure calculations. A sliding motion, within one out of the three (EDT-TTF-CONH2)2 dimers coupled to the [Re6Se8(CN6)(3-)·]/[Re6Se8(CN6)4-] proportion at any temperature, and the electronic ground state of the organic-inorganic hybrid material are analyzed on the basis of ESR, dc conductivity, ¹H spin-lattice relaxation, and static susceptibility data which qualify a Mon localization in [EDT-TTF-CONH2]6[Re6Se8(CN)6]. The coupling between the metal-insulator transition and a structural transition allows for the lifting of a degeneracy due to the ternary axis in the high temperature, strongly correlated metallic phase which, in turn, leads to Heisenberg chains at low temperature. [ABSTRACT FROM AUTHOR]

Studies the deliberate design of a series of single crystals of conducting two-dimensional radical cation salts of o-bis(amide)-appended ethylenedithiotetrathiafulvalene and of their parent monocomponent solid ethylenedithiotetrathiafulvalene. Presence of a robust and adaptable hydrogen bond network in single-component solids; Preservation of the slab topology in radical cation salts; Restoration of an organic-inorganic interface.

The ability of I···I van der Waals interactions to direct the self-assembly of slabs of the radical cation of ethylenedithio-1,2-diiodo-tetrathiafulvalene, EDT-TTF-I[sub 2], and polymeric lead iodide covalent anionic layers is demonstrated by the synthesis of single crystals of β-(EDT-TFF-I[sub 2])[sub 2, sup •+][(Pb[sub 5/6...1/6]I[sub 2])[sup 1/3-]][sub 3], triclinic, P-1, a = 7.7818(8), b = 7.9760(8), c = 19.9668(2) Å, α = 82.409(12), β = 85.964(12), γ = 61.621(11)°, V = 1080.76(19) ų, R1, wR2 = 0.0459, 0.0947; and β-(EDT-TTF-I[sub 2])[sub 2, sup •+][(Pb[sub 2/3+x]Ag[sub 1/3-2x...x] I[sub 2])[sup 1/3]][sub 3], x ≈ 0.05, triclinic, P-1, a = 7.7744(8), b = 7.9193(8), c = 19.834(2) Å, α = 87.189(12), β = 83.534(12), γ = 61.602(11)°, V = 1067.4(2) ų, R1, wR2 = 0.0508, 0.0997. The state-of-the-art, combined microprobe and structural analysis of the metal site vacancies and occupancies patterns reveal a commensurate organic-inorganic interface and point out the importance of halogen···halogen van der Waals interactions to future studies aiming at directing interface topologies. The electronic structure, room-temperature metallic character and metal-insulator transition at ca. 70 K of the two-dimensional organic slabs are retained upon alloying of the inorganic sublattice with monocations. The room-temperature conductivity of the metallic lead-silver alloy is 2 orders of magnitude larger than that of β-(EDT-TTF-I[sub 2])[sub 2, sup •+][(Pb[sub 5/6...1/6]I[sub 2])[sup 1/3-]][sub 3]. This calls for the study of materials with diverse alloying patterns with metal cations of different nature and charge. [ABSTRACT FROM AUTHOR]

The article discusses the syntheses, structure and properties of chiral molecular metals. Within the extended series of organic metals and superconductors based on tetrathiafulvalene (TTF) and derivatives, the introduction of chirality offers an invaluable opportunity to evaluate the role of disorder on the conductive properties since radical cation salts of enantiopure donors are expected to suffer less from structural disorder than those of racemates, where the crystal structure may tolerate the enantiomers exchanging places.

Electrocrystallization of the bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) organic donor in the presence of the [Fe(ClCNAn) 3 ] 3- tris(chlorocyananilato)ferrate(III) paramagnetic anion in different stoichiometric ratios and solvent mixtures afforded two different hybrid systems formulated as [BEDT-TTF] 4 [Fe(ClCNAn) 3 ]·3H 2 O ( 1 ) and [BEDT-TTF] 5 [Fe(ClCNAn) 3 ] 2 ·2CH 3 CN ( 2 ) (An = anilato). Compounds 1 and 2 present unusual structures without the typical segregated organic and inorganic layers, where layers of 1 are formed by Λ and Δ enantiomers of the anionic paramagnetic complex together with mixed-valence BEDT-TTF tetramers, while layers of 2 are formed by Λ and Δ enantiomers of the paramagnetic complex together with dicationic BEDT-TTF dimers and monomers. Compounds 1 and 2 show semiconducting behaviors with room-temperature conductivities of ca. 6 × 10 -3 S cm -1 (ambient pressure) and 1 × 10 -3 S cm -1 (under applied pressure of 12.1 GPa), respectively, due to strong dimerization between the donors. Magnetic measurements performed on compound 1 indicate weak antiferromagnetic coupling between high-spin Fe III ( S Fe = 5/2) and mixed-valence radical cation diyads (BEDT-TTF) 2 + ( S rad = 1/2) mediated by the anilate ligands, together with an important Pauli paramagnetism typical for conducting systems.

The mixed-valence Fe II Fe III 2D coordination polymer formulated as [TAG][Fe II Fe III (ClCNAn) 3 ]·(solvate) 1 (TAG = tris(amino)-guanidinium, ClCNAn 2- = chlorocyanoanilate dianionic ligand) crystallized in the polar trigonal space group P3. In the solid-state structure, determined both at 150 and at 10 K, anionic 2D honeycomb layers [Fe II Fe III (ClCNAn) 3 ] - establish in the ab plane, with an intralayer metal-metal distance of 7.860 Å, alternating with cationic layers of TAG. The similar Fe-O distances suggest electron delocalization and an average oxidation state of +2.5 for each Fe center. The cation imposes its C 3 symmetry to the structure and engages in intermolecular N-H···Cl hydrogen bonding with the ligand. Magnetic susceptibility characterization indicates magnetic ordering below 4 K and the presence of a hysteresis loop at 2 K with a coercive field of 60 Oe. Mössbauer measurements are in agreement with the existence of Fe(+2.5) ions at RT and statistic charge localization at 10 K. The compound shows semiconducting behavior with the in-plane conductivity of 2 × 10 -3 S/cm, 3 orders of magnitude higher than the perpendicular one. A small-polaron hopping model has been applied to a series of oxalate-type Fe II Fe III 2D coordination polymers, providing a clear explanation on the much higher conductivity of the anilate-based systems than the oxalate ones.

Molecular metals have been essentially obtained with tetrathiafulvalene (TTF)-based precursors, either with multicomponent ionic materials or, in a few instances, with single-component systems. In that respect, gold bis(dithiolene) complexes, in their neutral radical state, provide a prototype platform toward such single-component conductors. Herein we report the first single-component molecular metal under ambient pressure derived from such Au complexes without any TTF backbone. This complex exhibits a conductivity of 750 S·cm -1 at 300 K up to 3800 S·cm -1 at 4 K. First-principles electronic structure calculations show that the striking stability of the metallic state finds its origin in sizable internal electron transfer from the SOMO-1 to the SOMO of the complex as well as in substantial interstack and interlayer interactions.

Lithium cobalt oxide nanobatteries offer exciting prospects in the field of nonvolatile memories and neuromorphic circuits. However, the precise underlying resistive switching (RS) mechanism remains a matter of debate in two-terminal cells. Herein, intriguing results, obtained by secondary ion mass spectroscopy (SIMS) 3D imaging, clearly demonstrate that the RS mechanism corresponds to lithium migration toward the outside of the Li x CoO 2 layer. These observations are very well correlated with the observed insulator-to-metal transition of the oxide. Besides, smaller device area experimentally yields much faster switching kinetics, which is qualitatively well accounted for by a simple numerical simulation. Write/erase endurance is also highly improved with downscaling - much further than the present cycling life of usual lithium-ion batteries. Hence very attractive possibilities can be envisaged for this class of materials in nanoelectronics., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Neutral nickel bis(dithiolene) complexes, because of their closed-shell character, are usually considered as insulating materials, unless they are formed out of highly delocalized tetrathiafulvalenedithiolate ligands. We describe here an original series of S-alkyl substituted neutral bis(thiazole-4,5-dithiolate) nickel complexes formulated as [Ni(RS-tzdt)2] (R = Me, Et), which organize in the solid state into uniform stacks and exhibit semiconducting behavior, with room temperature conductivities comparable to those reported in the prototypical [Ni(dmit)2] and [Ni(Et-thiazdt)2] neutral complexes. These findings provide new perspectives in the current search for single component molecular conductors.

A mixed-valence conducting cation radical salt of the unsymmetrically substituted o -Me 2 TTF donor molecule (TTF is tetrathiafulvalene) was obtained upon electrocrystallization in the presence of the non-centrosymmetric NO 3 - anion. It crystallizes at room temperature in the monoclinic P 2 1 / c space group, with the anion disordered on an inversion centre. The donor molecules are stacked along the a axis. A 90° rotation of the longest molecular axis of o -Me 2 TTF generates a chessboard-like structure, preventing lateral S⋯S contacts between stacks and providing a strongly one-dimensional electronic system, as confirmed by overlap interaction energies and band structure calculations. A strong dimerization within the stacks explains the semi-conducting behaviour of the salt, with σ room temp = 3-5 S cm -1 and E activated = 0.12-0.14 eV. An X-ray diffuse scattering survey of reciprocal space, combined with full structure resolutions at low temperatures (250, 85 and 20 K), evidenced the succession of two structural transitions: a ferroelastic one with an anion-ordering (AO) process and the establishment of a (0, ½, ½) superstructure below 124 (±3) K, also visible via resistivity thermal dependence, followed by a stack tetramerization with the establishment of a (½, ½, ½) superstructure below 90 (±5) K. The latter ground state is driven by a spin-Peierls (SP) instability, as demonstrated by the temperature dependence of the magnetic susceptibility. Surprisingly, these two kinds of instability appear to be fully decoupled here, at variance with other tetra-methyl-tetra-thia-fulvalene (TMTTF) or tetramethyl-tetra-selena-fulvalene (TMTSF) salts with such non-centrosymmetric counter-ions.

Among single component molecular conductors, neutral radical gold dithiolene complexes [(R-thiazdt) 2 Au] . derived from the N-alkyl-1,3-thiazoline-2-thione-4,5-dithiolate (R-thiazdt) ligand provide an extensive series of conducting, non-dimerized, half-filled band systems. Analogues of the known R=isopropyl (iPr) derivative were investigated here with R=NMe 2 , cyclopropyl (cPr) and n-propyl (nPr), aiming at rationalizing the different solid state structures adopted by these compounds despite very closely related substituents on the heterocyclic nitrogen atom. An original crisscross organization within dimerized chains is observed with R=NMe 2 , differing however from the analogous iPr derivative by a 180° rotation of the heterocyclic nitrogen substituent. On the other hand, the cyclopropyl and n-propyl substituents lead to robust, uniform, non-dimerized chains with a strongly 1 D electronic structure and a formal half-filled electronic structure. The semiconducting behaviour of these two radical complexes is characteristic of a Mott insulator, whose sensitivity to external pressure has been evaluated up to 2.5 GPa., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Radical cation salts composed of a bis(ethylenedithio)tetrathiafulvalene (ET) donor with homo-/heterosubstituted Cl/CN anilic acids as purely organic molecular conducting materials formulated as [BEDT-TTF] 2 [HClCNAn] (1) and [BEDT-TTF][HCl 2 An] (2) have been prepared by electrocrystallization. Compounds 1 and 2 crystallized in the monoclinic space group P2/c for 1 and I2/a for 2, showing segregated donor-anion layers arranged in a α'-type donor packing pattern (1) and twisted parallel columns (2), respectively. Single-crystal conductivity measurements show that 1 is a semiconductor with room-temperature conductivity of 10 -2 S cm -1 and an activation energy E a of 1900 K.

While the introduction of large, bulky substituents such as tert-butyl, -SiMe3, or -Si(isopropyl)3 has been used recently to control the solid state structures and charge mobility of organic semiconductors, this crystal engineering strategy is usually avoided in molecular metals where a maximized overlap is sought. In order to investigate such steric effects in single component conductors, the ethyl group of the known [Au(Et-thiazdt)2] radical complex has been replaced by an isopropyl one to give a novel single component molecular conductor denoted [Au(iPr-thiazdt)2] (iPr-thiazdt: N-isopropyl-1,3-thiazoline-2-thione-4,5-dithiolate). It exhibits a very original stacked structure of crisscross molecules interacting laterally to give a truly three-dimensional network. This system is weakly conducting at ambient pressure (5 S·cm(-1)), and both transport and optical measurements evidence a slowly decreasing energy gap under applied pressure with a regime change around 1.5 GPa. In contrast with other conducting systems amenable to a metallic state under physical or chemical pressure, the Mott insulating state is stable here up to 4 GPa, a consequence of its peculiar electronic structure.

The first examples of chiral single component conductors are reported. Both (S,S) and (R,R) enantiomers of 5,6-dimethyl-5,6-dihydro-1,4-dithiin-2,3-dithiolate (dm-dddt) ligand have been used to prepare anionic metal bis(dithiolene) complexes formulated as ([(n-Bu)4N][M(dm-dddt)2] (M = Au, Ni), which are isostructural according to single crystal X-ray analysis. Single crystal transport measurements indicate semiconducting behavior for the anionic radical Ni complexes, with low room temperature conductivity values and high activation energies. Electrocrystallization experiments provided neutral [M(dm-dddt)2] (M = Au, Ni) complexes. The neutral radical gold compounds show intermolecular S···S interactions in the solid state giving rise to layers interconnected through weak C-H···S hydrogen bonds. The most peculiar structural feature concerns a dissymmetry between the two dithiolene moieties, while the nickel counterpart is symmetric. Single crystal resistivity measurements show thermally activated behavior for the open-shell gold complexes, with room temperature conductivity values of 0.02-0.04 S·cm(-1) and activation energies strongly influenced by hydrostatic pressure. A thorough theoretical study on nickel anion radical and gold neutral radical bis(dithiolene) complexes applied to the chiral complexes [M(dm-dddt)2] (M = Au, Ni(-)) and to a series of previously reported compounds addressed the issue of symmetry versus asymmetry from an electronic coupling perspective between the two dithiolene ligands. It results that neutral gold complexes with dithiolene ligands without extended delocalization are Class II mixed-valent compounds in the Robin and Day classification, presenting an inherent tendency toward asymmetric structures, which can be however modulated by the intermolecular organization in the solid state.

The Z and E isomers of the iodinated TTF derivative (Z,E)-Me2I2-TTF co-crystallize in a mixed-valence salt with Br(-) anions, and are segregated into Z and E stacks, each of them with a different charge localization pattern, which also revealed charge-assisted halogen bonding.

Control of band filling or doping of molecular (semi)conductors can be performed by substitutional insertion of molecules with a similar shape but a different electron count, with one more or one less electron. This strategy has been explored here within the semiconducting, single-component, radical gold dithiolene complex [AuOC4] bearing para-butoxyphenyl substituents. Alloying with the corresponding neutral nickel dithiolene complex [NiOC4] lacking one electron afforded a complete isostructural series [NiOC4]1-x[AuOC4]x, spanning the whole composition range from x = 0 to x = 1 by 0.1 increments, further characterized by X-ray diffraction and EDX analyses. Magnetic susceptibility data confirm the antiferromagnetic interactions between neighboring radical gold dithiolene complexes. The electrical conductivity increases exponentially with the x gold fraction, while the activation energy remains constant in the more conducting, gold-rich samples. This behavior is tentatively assigned to the tunneling barriers of variable width (with x) but of constant height, separating more conducting gold-rich segments. Comparison of redox potentials for the 1e(-) oxidation and reduction of both [NiOC4] and [AuOC4] dithiolene complexes indicates that the [NiOC4] nickel complex does not act as a dopant for the radical [AuOC4] complex.

Electrocrystallization of enantiopure (S,S,S,S)- and (R,R,R,R)-tetramethyl-bis(ethylenedithio)-tetrathiafulvalene (TM-BEDT-TTF) donors, as well as the racemic mixture, in the presence of potassium cations and the tris(chloranilato)ferrate(III) [Fe(Cl2An)3](3-) paramagnetic anion afforded a complete series of chiral magnetic molecular conductors formulated as β-[(S,S,S,S)-TM-BEDT-TTF]3PPh4[K(I)Fe(III)(Cl2An)3]·3H2O (1), β-[(R,R,R,R)-TM-BEDT-TTF]3PPh4[K(I)Fe(III)(Cl2An)3]·3H2O (2), and β-[(rac)-TM-BEDT-TTF]3PPh4[K(I)Fe(III)(Cl2An)3]·3H2O (3). Compounds 1-3 are isostructural and crystallize in triclinic space groups (P1 for 1 and 2, P-1 for 3) showing a segregated organic-inorganic crystal structure, where anionic honeycomb layers obtained by self-assembling of the Λ and Δ enantiomers of the paramagnetic complex with potassium cations alternate with organic layers where the chiral donors are arranged in the β packing motif. Compounds 1-3 show a molecular packing strongly influenced by the topology of the inorganic layers and behave as molecular semiconductors with room-temperature conductivity values of ca. 3 × 10(-4) S cm(-1). The magnetic properties are dominated by the paramagnetic S = 5/2 [Fe(Cl2An)3](3-) anions whose high-spin character is confirmed by magnetic susceptibility measurements. The correlation between crystal structure and conducting behavior has been studied by means of tight-binding band structure calculations which support the observed conducting properties.

A mixed-valence salt of tTTF-I with ClO4(-), formulated as (tTTF-I)2ClO4, is characterized by the presence of two crystallographically independent donor molecules, segregated in different layers and linked together through I···O interactions with the ClO4(-) anion disordered at room temperature. The tTTF-I donor molecule was prepared by metallation of tTTF (trimethylene tetrathiafulvalene) followed by reaction with iodine to afford the mono and diiodo derivatives tTTF-I and tTTFI2, respectively. The crystal structure of the latter neutral tTTFI2 shows the occurrence of strong type II, II halogen bond interactions. Band structure calculations of the dual-layer structure of the 2 : 1 salt (tTTF-I)2ClO4 show co-existence of both 1D open and 2D closed Fermi surfaces. The salt undergoes a metal-insulator phase transition at T(MI) = 90 K, associated with an electronic dimensionality decrease, since already at 100 K, the 2D part of the Fermi surface transforms into 1D corrugated planes. High resolution X-ray investigations performed at 100 K, combined with multipolar refinements, indicate an approximately equivalent +0.5e charge in both donor molecules, as also deduced from the intramolecular bond distances. On the other hand, Raman spectroscopic investigations show that at ambient temperature the charge is actually distributed non-uniformly in conducting layers of tTTF-I molecules, with the identification of molecules with charges +1, +0.5, 0e, while at low temperature the charge distribution becomes essentially uniform (+0.5e), as confirmed from the X-ray high resolution data. These apparently contradictory behaviors are actually a consequence of a partial electron transfer between the two independent slabs to reach a common Fermi level in the metallic phase.

Oxidation of diiodoethylenedithiotetrathiafulvalene (EDT-TTF-I2), C8H4I2S6, with the strong oxidizer tetrafluorotetracyanoquinodimethane (TCNQF4), C12F4N4, affords, depending on the crystallization solvent, two polymorphs of the 2:1 charge-transfer salt (EDT-TTF-I2)2(TCNQF4), represented as D2A. In both salts, the TCNQF4 is reduced to the radical anion state, and is associated through short C-I...NC halogen bonds to two EDT-TTF-I2 molecules. The two polymorphs differ in the solid-state association of these trimeric D-A-D motifs. In polymorph (I) the trimeric motif is located on an inversion centre, and hence both EDT-TTF-I2 molecules have +0.5 charge. Together with segregation of the TTF and TCNQ derivatives into stacks, this leads to a charge-transfer salt with high conductivity. In polymorph (II) two crystallographically independent EDT-TTF-I2 molecules bear different charges, close to 0 and +1, as deduced from an established correlation between intramolecular bond lengths and charge. Overlap interactions between the halogen-bonded D(0)-A-∙D+∙ motifs give rise, in a perpendicular direction, to diamagnetic A2(2-) and D(0)-D2(2+)-D(0) entities, where the radical species are paired into the bonding combination of respectively the acceptor LUMOs and donor HOMOs. The strikingly different solid-state organization of the halogen-bonded D-A-D motifs provides an illustrative example of two modes of face-to-face interaction between π-type radicals, into either delocalized, uniform chains with partial charge transfer and conducting behaviour, or localized association of radicals into face-to-face A2(2-) and D2(2+) dyads.

Charge-assisted halogen bonding is unambiguously revealed from structural and electronic investigations of a series of isostructural charge-transfer complexes derived from iodinated tetrathiafulvalene and tetracyanoquinodimethane derivatives, (EDT-TTFI2)2(TCNQF(n)), n=0-2, which exhibit variable degrees of ionicity. The iodinated tetrathiafulvalene derivative, EDT-TTFI2, associates with tetracyanoquinodimethane (TCNQ) and its derivatives of increasing reduction potential (TCNQF, TCNQF2) through highly directional C-I⋅⋅⋅N≡C halogen-bond interactions. With the less oxidizing TCNQ acceptor, a neutral and insulating charge-transfer complex is isolated whereas with the more oxidizing TCNQF2 acceptor, an ionic, highly conducting charge-transfer salt is found, both of 2:1 stoichiometry and isostructural with the intermediate TCNQF complex, in which a neutral-ionic conversion takes place upon cooling. A correlation between the degree of charge transfer and the C-I⋅⋅⋅N≡C halogen-bond strength is established from the comparison of the structures of the three isostructural complexes at temperatures from 300 to 20 K, thus demonstrating the importance of electrostatics in the halogen-bonding interaction. The neutral-ionic conversion in (EDT-TTFI2)2(TCNQF) is further investigated through the temperature dependence of its magnetic susceptibility and the stretching modes of the C≡N groups., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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., (© 2011 American Chemical Society)

The reactivity of the redox-active tetracarboxylic acid derived from the tetrathiafulvalene (TTF-TC)H(4) with alkaline cations (K, Rb, Cs) is reported. The exploration of various experimental parameters (temperature, pH) led to the formation of four crystalline three-dimensional coordination polymers formulated M(2)(TTF-TC)H(2) (M = K, Rb, Cs), denoted MIL-132(K), MIL-133(isostructural K, Rb), and MIL-134(Cs). Thermogravimetric analysis and thermodiffraction show that all of the solids are thermally stable up to 150-200 degrees C in the air. In order to exploit the possibility of oxidation of the organic linker in TTF-based compounds, they were employed as positive electrodes in a classical lithium cell. A highly reversible cyclability was achieved at high current density (10 C) with a reasonable performance (approximately 50 mAh g(-1)). Finally, combined electro-(sub)hydrothermal synthesis was used to prepare a fifth 3-D coordination polymer formulated K(TTF-TC)H(2) (denoted MIL-135(K)), this time not based on the neutral TTF-TC linker but its radical, oxidized form TTF-TC(+*). This solid is less thermally stable than its neutral counterparts but exhibits a semiconducting behavior, with a conductivity at room temperature of about 1 mS cm(-1).

Syntheses, X-ray structural analyses, thermal behaviors, photochromism, and electrical properties of a series of methylviologen (MV(2+)) halobismuthate hybrids, namely, (MV)(3)[Bi(4)Cl(18)](H(2)O)(y) (1a, y approximately = 1.7), (MV)(4)[Bi(6)Cl(26)](H(2)O)(y) (2a, y approximately = 1.7), (MV)(4)[Bi(6)Cl(25.6)I(0.4)](H(2)O)(y) (3a, y approximately = 1.5), and (MV)(4)[Bi(6)Cl(24.6)I(1.4)](H(2)O)(y) (4a, y approximately = 1.3), are reported. Because of the thermal effect of a UV lamp or as a result of being heated up to 100 degrees C, all of the above compounds undergo a complete (1a, 2a, and 3a) or a partial (4a) dehydration together, in 2a and 3a, with an impressive structural reorganization involving a 90 degrees rotation of methylviologen dimers and, in 3a, a new Cl/I distribution, finally leading to (MV)(3)[Bi(4)Cl(18)] (1b), (MV)(4)[Bi(6)Cl(26)] (2b), (MV)(4)[Bi(6)Cl(25.6)I(0.4)] (3b), and (MV)(4)[Bi(6)Cl(24.6)I(1.4)](H(2)O)(x) (4a, x approximately = 0.65), respectively. In its turn, 4a (x approximately = 0.65) undergoes an abrupt structural change at 160 degrees C when water molecules are completely removed, leading to (MV)(4)[Bi(6)Cl(24.6)I(1.4)] (4b). Obviously, the two first dehydrated phases can be considered as the n = 2 (1b) and n = 3 (2b) members of the (MV)((2n+2)/2)[Bi(2n)Cl(8n+2)] family, and the ultimate member (n = infinity) with an infinite 1D double-chain inorganic framework, namely, (MV)[Bi(2)Cl(8)], has already been reported. According to the results of structural refinements, some positions of the Cl atoms in the [Bi(6)Cl(26)](8-) anionic cluster of 3a and 4a have been occupied by I atoms, finally leading to iodide-doped materials of the 2a type (percentage of doping: 3a, 1.5%; 4a, 5.4%). Upon UV irradiation, yellow crystals of 2a and 3a (which become 2b and 3b because of the thermal effect of the UV lamp) or yellow crystals of 2b, 3b, and 4a undergo a color change to black crystals (in the case of 2b), as observed in (MV)[Bi(2)Cl(8)], or light-brown crystals (in the cases of 3b and 4a). These photochromic properties are probably due to the photoinduced electron transfer from the anionic part to the methylviologen dications. In contrast, no color change is observed when yellow crystals of 1a or 1b and the iodide-doped (MV)[Bi(2)Cl(8-epsilon)I(epsilon)] material are irradiated. Because the relative positions of methylviologen to the host anionic frameworks are comparable in all structures (the N...Cl distances are about 3.4 A), these results indicate that such kinds of photochemical reactions depend on the dimension of the anionic networks, as well as the iodide doping. The single-crystal electrical conductivity measurements of 2b before and after irradiation were carried out between 150 and 393 K. The results prove that both of them are semiconductors with weak room temperature conductivity and that the band gap of the irradiated crystal (2b, 0.35 eV) is much smaller than that of the original hybrid 2a (1.0 eV).

Electrocrystallization experiments with the chiral ethylenedithio-tetrathiafulvalene-methyl-oxazoline (EDT-TTF-OX) donors (R)-, (S)-, and (rac)-1 have provided two series of mixed-valence salts with the PF(6) (-) and [Au(CN)(2)](-) anions. Within each series the cell parameters are the same for the three R, S, and rac compounds, except for the space group, which is centrosymmetric triclinic P$\bar 1$ for the racemic forms and noncentrosymmetric P1 for the enantiopure salts. In the racemic salt [(rac)-1](2)PF(6) the two enantiomers crystallize disordered on the same crystallographic site with a site occupational factor of 0.6:0.4, whereas this type of disorder is not possible in the enantiopure salts. Both s-cis and s-trans conformations, when taking into account the mutual orientation of the TTF and oxazoline moieties, are present in this first series. In sharp contrast, in the series of salts [1](2)[Au(CN)(2)], only the s-trans conformation is observed with no structural disorder. Theoretical calculations at the DFT level of theory revealed a very small energy difference between the two stable planar s-cis and s-trans conformations, which are both energy minima in either neutral or oxidized states. Single-crystal conductivity measurements showed metallic-like behavior for all the salts down to 220-250 K with a smooth increase in resistivity at lower temperatures. The conductivity at room temperature is 5 S cm(-1) for [(rac)-1](2)PF(6), in which disorder was observed, whereas for [(R)-1](2)PF(6) and [(S)-1](2)PF(6) the average value is around 100 S cm(-1). In the second series of salts the conductivity at room temperature is 125-130 S cm(-1) for [(rac)-1](2)[Au(CN)(2)] and [(R)-1](2)[Au(CN)(2)]. Extended Hückel band structure calculations revealed identical features for the three salts of the [1](2)[Au(CN)(2)] series and are consistent with the electronic structures of quasi-one-dimensional conductors.

A single component molecular conductor has been isolated from electrocrystallization of the monoanionic gold bis(dithiolene) complex based on the N-ethyl-1,3-thiazoline-2-thione-4,5-dithiolate (Et-thiazdt) ligand. The crystal structure of the system exhibits layers built from parallel uniform one-dimensional stacks of the planar molecule. At room temperature and ambient pressure the system is semiconducting (0.33 S x cm(-1)) with a small activation energy. However, the single crystal conductivity is strongly pressure dependent reaching 1000 S x cm(-1) at 21 kbar. At 13 kbar there is a crossover between semiconducting and metallic regimes. Thus, the present system is the first well characterized single-component molecular metal without TTF dithiolate ligands. First-principles DFT calculations show that the ground state is antiferromagnetic with a very small band gap. A simulation of the effect of pressure on the electronic structure provides a rationale for the observed variations of the conductivity and gives insight on how to further stabilize the metallic state of the system.

Complementary shapes of the neutral symmetrical halogen-bond bis-donor core and octahedral inorganic cluster core prevent halogen-bonded polymers developing in more than one direction, favouring further templating by conducting radical cation slabs and yielding an 8 : 1 : 1 phase formulation instead of n : 2 : 1, with a 2D net, or m : 3 : 1, with a pseudo-cubic architecture, which may in principle also be targeted.

The synthesis and characterization of two ortho-dimethyltetrathiafulvalene (o-DMTTF)-based rigid dimers containing dimethylsilicon (Me(2)Si) or dimethylgermanium (Me(2)Ge) linkers are described. Single-crystal X-ray analysis reveals planar geometry for the central 1,4-disilicon or 1,4-digermanium six-membered rings. DFT calculations provide optimized conformations in agreement with the experimental ones, and also emphasize the role of the heteroatomic linkers in the conjugation between the two redox active units. Cyclic voltammetry measurements show sequential oxidation into radical cation, and then dication species. Solution EPR measurements on the radical-cation species indicate full delocalization of the unpaired electron over both electroactive TTF units, with an associated coupling of 0.42 G with twelve equivalent protons. DFT calculations afford fully planar geometry for the radical-cation species and confirm the experimental isotropic coupling constant. Single-crystal X-ray analyses of two charge-transfer compounds obtained upon chemical oxidation, formulated as [(Me(2)Si)(2)(o-DMTTF)(2)].1/2[TCNQ].1/2[TCNQF(4)] and [(Me(2)Ge)(2)(o-DMTTF)(2)].[TCNQ], demonstrate the occurrence of genuine mixed-valence radical-cation species, as well as a three-dimensional network of short S...S intermolecular contacts. Temperature-dependent conductivity measurements demonstrate semiconducting behavior for both charge-transfer compounds, with an increase of the absolute value of the conductivity upon applying external pressure. Band structure calculations reveal peculiar pseudo-two-dimensional electronic structures, also confirming electronic interactions through SiMe(2) and GeMe(2) bridges.

The solid-state chemistry of a series of seven ortho-bis(alkylamido)ethylenedithiotetrathiafulvalene derivatives EDT-TTF-(CONHR)2 (R=Me, 1; Et, 2; Pr, 3; Bu, 4; Pent, 5; Hex, 6; and Bz, 7), in their neutral and one-electron-oxidized, radical cation states, was investigated with an eye on the topology of intra- and intermolecular hydrogen-bond motifs. In the case of neutral, monomolecular solids, an intramolecular N--H.O hydrogen bond seals a constrained seven-membered ring for 1, 2, 3, and 7, which is disrupted in butyl derivative 4 in favor of an antiparallel ladder at the expense of any intramolecular hydrogen bond. In the solid-state, the competition between intra- and intermolecular hydrogen bonding observed in solution depends on the packing of the molecules. Electrocrystallization of methyl derivative 1 with ReO4- or ClO4-, two anions of different volumes but otherwise identical charge and symmetry, revealed a fine sensitivity of the constrained seven-membered ring to the internal chemical pressure exerted by the anion. [1]2 *+ReO4 (sigmaRT=8.5 S cm(-1), activation energy Delta=600 K at high temperature) and beta"-[1]2 *+ClO4 (sigmaRT=0.03 S cm(-1), Delta=1600 K; under pressure at room temperature, the conductivity increases by three orders of magnitude up to 17 kbar with a linear variation of the activation energy with pressure, Delta=aP with a=0.202 10(6) K kbar(-1)) have vastly different architectures, dimensionalities, electronic structures, and collective properties, a consequence of the presence of the closed or open structural isomers in one or the other. This exemplifies the flexibility of functionalized TTF derivatives, even when the functional group is directly attached to the electro-active core. This allows an analogy to be drawn with tetrafunctionalized metallocenes, in which such flexibility has already been observed. The experimental data are supported by theoretical calculations of the energy profile of a model molecule on rotation of the amido groups.

An in-depth analysis of a set of 21 layered structures of metallic pseudopolymorphs of general formulation, beta''-(BEDT-TTF)(4) x (guest)(n) x [Re(6)Q(6)Cl(8)], (BEDT-TTF=bis-ethylenedithiotetrathiafulvalene; Q = S, Se; guest = H(2)O, 1,4-dioxane, THF, CCl(4), C(2)H(5)OH, CHCl(3), CH(2)ClI, CH(2)ClBr, CH(2)Cl(2), CH(2)OH-CH(2)OH, C(5)H(5)N, CH(3)COCH(3), 2-hydroxy-tetrahydrofuran, CH(3)CN, CS(2), C(6)H(6)), with diverse low-temperature behaviors, which differ solely by the nature of the cosolvent molecule selectively included during the electrocrystallization process, reveals a precise set of weak HO-H...Cl-mu-Re, (C-H)(BEDT-TTF)...Cl-mu-Re, C-H...O(guest), (C-H)(guest)...Cl-mu-Re hydrogen bonds at the organic-inorganic interface, none of which dominates any of the others and whose balance is adjusted upon substitution of one guest molecule by another. The electronic structure of the host adjusts to the weak perturbation imposed by exchanging the guest molecules and by balancing the former interfacial interactions; this correlates to a net activation of up to 0.1 eV of the energy of the HOMO level of one of the two donors, while keeping the pattern of HOMO-HOMO intermolecular interactions in the donor layer essentially unaltered. It is suggested that this controls the stability of the metallic state at low temperature or the occurrence of a metal-to-insulator phase transition for particular guests along the series. It is concluded that by allowing for numerous tiny modifications at the organic-inorganic interface within a single, robust host structure, one sees a concerted, inherently weak structural response of the system that is proportional to the magnitude of the underlying, equally weak activation of the HOMO energy of a fraction of the pi-donor molecules within the slabs; this has a sizeable influence on the macroscopic transport properties of the system.