A three-dimensional synthetic metallic crystal composed of single-component molecules

Solubility-Limited Small Molecule for Stable High-Capacity Potassium Storage

Small molecule electrode materials with superb redox activity have significant applied implications for K-ion storage, but they face significant challenges like high solubility in electrolytes and low conductivity, limiting their capacity, rate, and cycling stability. Herein, a series of Ni-bis(dithiolene) (NiS4)-based small molecules are designed with control of various redox-active substitutional groups for K-ion batteries anode materials. It is identified that bis[1,2-di(pyridine-4-yl) ethylene-1,2-dithiolate] nickel Ni[C2S2Py2]2 demonstrates a high reversible specific capacity (399 mAh g-1 at 0.03 A g-1) with an impressive rate capability and an exceptional cycling stability (over 99% capacity retention after 1600 cycles). Its extraordinary performance is attributed to the synergy between the NiS4 unit and pyridine group, providing abundant K⁺ storage sites, impressive conductivity, and low solubility. The comprehensive characterizations and theoretical simulation confirm the multistep K⁺ storage mechanism in Ni[C2S2Py2]2, enabling fast charge transfer and excellent rate performance. This work offers new perspectives in building solubility-limited and conductive small molecule electrode materials with high redox activity for non-aqueous rechargeable batteries.

Ultra-highly conductive optoelectronic modulated single-molecule nickel bis(dithiolene) junctions with strong molecule-electrode coupling

Strong molecule-electrode coupling originating from orbit hybridization between gold and the delocalized molecular wires in single-molecule junctions facilitates facile transport towards smart molecular devices. In this paper, we report ultra-highly conductive single-molecule circuits based on highly delocalized nickel bis(dithiolene) (NiS4) molecular junctions using scanning tunneling microscope break junction technique. Single-molecule charge transport measurement of both NiS4 reveals they exhibits high conductance of 10-1.49G0 and 10-1.51G0, respectively. Moreover, under intervention of high bias voltage the molecular conductance could be further improved to approximately 10-1.00G0, the highest value reported to date with similar molecular lengths. Theoretical calculations suggest that the strong hybridization of the π-channels and the gold electrodes in both junctions exists and it further extends from molecule-electrode interfaces to metal electrodes as visualized by the isosurface plots of the transmitting eigenstate, which lead to not only a distinct energy shift of the dominated LUMO peaks toward Fermi level, but also broad peaks in the LUMO resonance in the transmission functions. In addition, the both molecular junctions show remarkable photoconductance of approximately 10-1.00G0 under resonant light excitation, due to possible exciton binding in these junctions. Interestingly, the conductance switching of both molecular junctions under optoelectronic modulation is highly reversible, forming a multi-stimulus responsive molecular switch. This work not only provides a building block for fabricating highly conducting molecular wires with strong molecule-electrode coupling, but also lays a foundation for designing optoelectronic modulated functional molecule-scale devices.

Polymorph transformation in a mixed-stacking nickel-dithiolene complex with the derivative of 4,4'-bipyridinium

In this study, two polymorphs of the [1,1'-dibutyl-4,4'-bipyridinium][Ni(mnt)2] salt (1) were synthesized. The dark-green polymorph (designated as 1-g) was prepared under ambient conditions by the rapid precipitation method in aqueous solutions. Subsequently, the red polymorph (labeled as 1-r) was obtained by subjecting 1-g to ultrasonication in MeOH at room temperature. Microanalysis, infrared spectroscopy, thermogravimetry (TG), differential scanning calorimetry (DSC), and powder X-ray diffraction (PXRD) techniques were used to characterize the two polymorphs. Both 1-g and 1-r exhibit structural phase transitions: a reversible phase transition at ∼403 K (∼268 K) upon heating and 384 K (∼252 K) upon cooling for 1-g (1-r) within the temperature range below 473 K. Interestingly, on heating 1-r to 523 K, an irreversible phase transition occurred at about 494 K, resulting in the conversion of 1-r into 1-g. Relative to 1-r, 1-g represents a thermodynamically metastable phase wherein numerous high-energy conformations in butyl chains of cations are confined within the lattice owing to quick precipitation or rapid annealing from higher temperatures. Through variable-temperature single crystal and powder X-ray diffractions, UV-visible spectroscopy, dielectric spectroscopy, and DSC analyses, this study delves into the mechanism underlying phase transitions for each polymorph and the manual transformation between 1-g and 1-r as well.

An organic superconductor, (TEA)(HEDO-TTF-dc)2·2(H2C2O4), coupled with strong hydrogen-bonding interactions

A new organic superconductor (TEA)(HEDO-TTF-dc)₂·2(H₂C₂O₄) (H₂EDO-TTF-dc = ethylenedioxy-tetrathiafulvalene dicarboxylic acids) with an onset T_C of 4.0 K, was successfully obtained using oxalic acid and HEDO-TTF-dc anion donor. The crystal structure analysis indicated that strong π-π overlaps and very strong intra- and inter-molecular hydrogen-bonding interactions exist between the HEDO-TTF-dc anion donors and oxalic acid molecules.

Graphite-like Charge Storage Mechanism in a 2D π-d Conjugated Metal-Organic Framework Revealed by Stepwise Magnetic Monitoring

Quasi-two-dimensional (2D) fully π-d conjugated metal-organic frameworks (MOFs) have been widely employed as active materials of secondary batteries; however, the origin of their high charge storage capacity is still unknown. Some reports have proposed a mechanism by assuming the formation of multiple radicals on one organic ligand, although there is no firm evidence for such a mechanism, which would run counter to the resonance theory. In this work, we utilized various magnetometric techniques to monitor the formation and concentration of paramagnetic species during the electrochemical process of 2D π-d conjugated Cu-THQ MOF (THQ = tetrahydroxy-1,4-benzoquinone). The spin concentration of the fully reduced (discharged 1.5 V) electrode was estimated to be around only 0.1 spin-1/2 per CuO₄ unit, which is much lower than that of the expected "diradical" form. More interestingly, a significant elevation of the temperature-independent paramagnetic term was simultaneously observed, which indicates the presence of delocalized π electrons in this discharged state. Such results were corroborated by first-principles density functional theory calculations and the electrochemically active density of states, which reveal the microscopic mechanism of the charge storage in the Cu-THQ MOF. Hence, a graphite-like charge storage mechanism, where the π-electron band accepts/donates electrons during the charge/discharge process, was suggested to explain the excessive charge storage of Cu-THQ. This graphite-like charge storage mechanism revealed by magnetic studies can be readily generalized to other π-d conjugated MOFs.

Crystal structure of 1,1′-(1,2-ethanediyl)bis(pyridin-1-ium) bis(1,2-dicyanoethene-1,2-dithiolato-κ2 S:S)zinc(II), C20H14N6ZnS4

C20H14N6ZnS4, monoclinic, C2/c (no. 15), a = 8.5063(13) Å, b = 12.3254(19) Å, c = 21.843(3) Å, β = 96.550(2)°, V = 2275.1(6) Å3, Z = 4, R gt (F) = 0.0288, wR ref (F 2) = 0.0751, T = 293(2) K.

Synthesis and coordination behaviour of 1H-1,2,3-triazole-4,5-dithiolates

The preparative access to and first group 10 metal complexes of novel 1H-1,2,3-triazole-4,5-dithiolate ligands (tazdt^2-) are reported. A set of S-protected 1H-1,2,3-triazole-4,5-dithiol derivatives with R¹ = 2,6-dimethylphenyl (Xy) or benzyl (Bn) at N1 and with R² = Bn or trimethylsilylethyl (TMS-ethyl) at both S atoms were synthesized by a 1,3-dipolar cycloaddition catalysed by either Ru(II) or Cu(I). Extensive investigations on the removal of the protective groups resulted the reductive removal of benzyl groups to be superior in isolating the free 4,5-dithiols of R¹N₃C₂(SH)₂ with R¹ = Xy (H₂-8) or Bn (H₂-9). Coordination of these ligands led to the formation of the metal complexes [(η⁵-C₅H₅)₂Ti(8)], [Ni(dppe)(8)], [Ni(dppe)(9)], [Pd(dppe)(9)] {dppe = bis(diphenylphosphanyl)ethane} and homoleptic (NBu₄)_n[Ni(8)₂] (n = 1, 2). All complexes were fully characterized including structure determination by single crystal XRD. The electronic properties of the Ni and Pd complexes were determined by cyclic voltammetry, UV/vis and EPR spectroscopy supported by DFT calculations. According to the spectral and electrochemical data, the tazdt^2- complexes resemble the corresponding benzene-1,2-dithiolate (bdt^2-) type compounds reflecting the restricted influence of the electron-withdrawing N₃ moiety in the backbone. DSC-TGA measurements with [(η⁵-C₅H₅)₂Ti(8)] and [Ni(dppe)(8)] indicate a well-defined thermal process involving simultaneous elimination of both N₂ and CS.

Zero-Overpotential Redox Reactions of Quinone-Based Molecules Confined in Carbon Micropores

Quinone-based aromatic compounds have been studied as electrode materials for various energy-storage devices. However, the relatively large activation barrier of the charge-transfer process of these redox-active molecules causes sluggish reactions and a decrease in energy efficiency. To lower the activation barrier, aromatic compounds must be strongly adsorbed on the electrode surface, preferably via π-π stacking interactions. Molecules in slit-shaped micropores strongly adsorb on the graphitic walls, thus experiencing unique micropore-confinement properties. In this study, the micropore-confinement effect is extended to the adsorption of quinone-based redox-active molecules in 0.8 nm slit-shaped micropores of activated carbon, which produces a drastic reduction in the activation barrier of the charge-transfer process and creates a zero-overpotential redox reaction. The property originates from the short distance (approximately 0.3 nm) between the quinone molecules and the graphitic wall due to the strong adsorption of the aromatic compound. Our results provide the first demonstration that the micropore-confinement effect can reduce and nearly eliminate the activation barrier of an electrochemical reaction. We also demonstrate the applicability of this approach via the charge/discharge performance of a two-electrode cell. Cells comprising the aromatic compound/activated carbon material as positive and negative electrodes exhibit a greater retention capacity than those without activated carbon. The technique described herein can guide the development of high-performance, rapid charging/discharging electrodes for energy-storage devices such as batteries, supercapacitors, and hybrid devices using organic materials.

Inspired by Nature-Functional Analogues of Molybdenum and Tungsten-Dependent Oxidoreductases

Throughout the previous ten years many scientists took inspiration from natural molybdenum and tungsten-dependent oxidoreductases to build functional active site analogues. These studies not only led to an ever more detailed mechanistic understanding of the biological template, but also paved the way to atypical selectivity and activity, such as catalytic hydrogen evolution. This review is aimed at representing the last decade’s progress in the research of and with molybdenum and tungsten functional model compounds. The portrayed systems, organized according to their ability to facilitate typical and artificial enzyme reactions, comprise complexes with non-innocent dithiolene ligands, resembling molybdopterin, as well as entirely non-natural nitrogen, oxygen, and/or sulfur bearing chelating donor ligands. All model compounds receive individual attention, highlighting the specific novelty that each provides for our understanding of the enzymatic mechanisms, such as oxygen atom transfer and proton-coupled electron transfer, or that each presents for exploiting new and useful catalytic capability. Overall, a shift in the application of these model compounds towards uncommon reactions is noted, the latter are comprehensively discussed.

An Approach to an Ideal Molecule-Based Mixed Conductor with Comparable Proton and Electron Conductivity

We synthesized a molecule-based proton-electron mixed conductor (PEMC), a Pt(III) dithiolate complex with 1,4-naphthoquinone skeletons. The π-planar Pt complex involves a π-stacking column, which is connected by one-dimensional hydrogen bonding chains composed of water molecules. The room-temperature (RT) proton conductivity is 8.0 × 10^-5 S cm^-1 under ambient conditions, which is >2 orders of magnitude higher than that of the isomorphous Ni complex (7.2 × 10^-7 S cm^-1). The smaller activation energy (0.23 eV) compared to that of the Ni complex (0.42 eV) possibly originates from the less dense water, which promotes the reorientational dynamics, in the Pt complex with an expanded lattice, namely, negative chemical pressure upon substitution of Ni with the larger Pt. In addition, the Pt complex shows a relatively high RT electronic conductivity of 1.0 × 10^-3 S cm^-1 caused by the π-columns, approaching an ideal PEMC with comparable proton and electron conduction.

Crystal structure of 1,1′-(methylene)bis(pyridin-1-ium) bis(1,2-dicyanoethene-1,2-dithiolato-κ2 S:S)nickel(II), C42H30N14Ni2S8

C42H30N14Ni2S8, triclinic, P 1 ‾ $P\overline{1}$ (no. 2), a = 9.5083(17) Å, b = 10.744(2) Å, c = 12.188(2) Å, α = 80.109(4)°, β = 84.876(4)°, γ = 88.758(3)°, V = 1221.7(4) Å3, Z = 1, R gt (F) = 0.0268, wR ref(F 2) = 0.0701, T = 296.15 K.

Indeno[2,1-a]fluorene-11,12-dione radical anions:synthesis,characterization and property

The one-electron reduction reactions of indeno[2,1-a]fluorene-11,12-dione ( IF ) with various alkali metals bring about the radical anion salts. The different structures and properties are characterized by single crystal X-ray diffraction, electron paramagnetic resonance (EPR) spectroscopy, superconducting quantum interference device (SQUID) measurements and physical property measurement system (PPMS). IF •- K + (18-c-6) is regarded as a one-dimensional magnetic chain through C-H-C interaction. Theoretical calculations and magnetic results prove that [ IF •- K + (15-c-5)] 2 is a dimer with an open-shell ground state. IF •- Na + (15-c-5) and IF •- K + (cryptand) are monoradical anion salts. IF 2 •- Li + possesses unique π-stack structure with an interplanar separation less than 3.46 Å, making it a semiconductor ( δ RT = 1.9 Χ 10 -4 S•cm -1 ). This work gives a wealth of insights into multifunctional radical anions, and makes the design and development of different functional radicals attractive.

Modern History of Organic Conductors: An Overview

This short review article provides the reader with a summary of the history of organic conductors. To retain a neutral and objective point of view regarding the history, background, novelty, and details of each research subject within this field, a thousand references have been cited with full titles and arranged in chronological order. Among the research conducted over ~70 years, topics from the last two decades are discussed in more detail than the rest. Unlike other papers in this issue, this review will help readers to understand the origin of each topic within the field of organic conductors and how they have evolved. Due to the advancements achieved over these 70 years, the field is nearing new horizons. As history is often a reflection of the future, this review is expected to show the future directions of this research field.

Introducing Selenium in Single-Component Molecular Conductors Based on Nickel Bis(dithiolene) Complexes

Two selenated analogues of the all-sulfur single-component molecular conductor [Ni(Et-thiazdt)₂] (Et-thiazdt = N-ethylthiazoline-2-thione-4,5-dithiolate) have been prepared from their precursor radical-anion complexes. Replacement of the thione by a selenone moiety gives the neutral [Ni(Et-thiazSedt)₂] complex. It adopts an unprecedented solid-state organization (for neutral nickel complexes), with the formation of perfectly eclipsed dimers and very short intermolecular Se···Se contacts (81% of the van der Waals contact distance). Limited interactions between dimers leads to a large semiconducting gap and low conductivity (σ_RT = 1.7 × 10^-5 S cm^-1). On the other hand, going from the neutral [Ni(Et-thiazdt)₂] dithiolene complex to the corresponding [Ni(Et-thiazds)₂] diselenolene complex gives rise to a more conventional layered structure built out of uniform stacks of the diselenolene complexes, different, however, from the all-sulfur analogue [Ni(Et-thiazdt)₂]. Band structure calculations show an essentially 1D electronic structure with large band dispersion and a small HOMO-LUMO gap. Under high pressures (up to 19 GPa), the conductivity increases by 4 orders of magnitude and the activation energy is decreased from 120 meV to only 13 meV, with an abrupt change observed around 10 GPa, suggesting a structural phase transition under pressure.

Changes in Surface Free Energy and Surface Conductivity of Carbon Nanotube/Polyimide Nanocomposite Films Induced by UV Irradiation

Changes in surface energy and electrical conductivity of polyimide (PI)-based nanocomposite films filled with carbon nanotubes (CNTs) induced by UV exposure are gaining considerable interest in microelectronic, aeronautical, and aerospace applications. However, the underlying mechanism of PI photochemistry and oxidation reactions induced by UV irradiation upon the surface in the presence of CNTs is still not clear. Here, we probed the interplay between CNTs and PIs under UV exposure in the surface properties of CNT/PI nanocomposite films. Changes in contact angles and surface electrical conductivity at the surface of CNT/PI nanocomposite films after UV exposure were measured. The unpaired electron intensity of free radicals generated by UV exposure was monitored by electron paramagnetic resonance. Our study indicates that the covalent interactions between CNTs and radicals generated by UV irradiation on the PI surfaces tailor the surface energy and surface conductivity through anchoring radicals on CNTs. Surprisingly, adding CNTs into PI films exposed to UV leads to antagonistic contributions of dispersion and polar components to the surface energy. The surface electrical conductivity of the CNT/PI nanocomposite films has been improved due to an enhanced hopping behavior with dense π-conjugated CNT sites. To explain the observed changes in surface energy and surface conductivity of CNT/PI nanocomposite films induced by UV exposure, a qualitative model was put forward describing the covalent interactions between UV-induced PI free radicals and CNTs, which govern the chemical nature of surface components. This study is helpful for characterizing and optimizing nanocomposite surface properties by tuning the covalent interactions between components at the nanoscale.

Crystal structure of 1,1′-(1,4-phenylenebis(methylene))bis(pyridin-1-ium) bis(1,2-dicyanoethene-1,2-dithiolato-k2 S:S)zinc(II), C26H18N6ZnS4

C26H18N6ZnS4, triclinic, P 1 ‾ $P‾{1}$ (no. 2), a = 9.4677(13) Å, b = 12.0147(17) Å, c = 13.571(3) Å, α = 102.907(3)°, β = 102.302(3)°, γ = 110.419(2)°, V = 1336.7(4) Å3, Z = 2, R gt (F) = 0.0441, wR ref (F 2) = 0.1202, T = 296(2) K.

Rare-Earth Metal Tetrathiafulvalene Carboxylate Frameworks as Redox-Switchable Single-Molecule Magnets

Using the redox-active tetrathiafulvalene tetrabenzoate (TTFTB^4- ) as the linker, a series of stable and porous rare-earth metal-organic frameworks (RE-MOFs), [RE₉ (μ₃ -OH)₁₃ (μ₃ -O)(H₂ O)₉ (TTFTB)₃ ] (1-RE, where RE=Y, Sm, Gd, Tb, Dy, Ho, and Er) were constructed. The RE₉ (μ₃ -OH)₁₃ (μ₃ -O) (H₂ O)₉ ](CO₂ )₁₂ clusters within 1-RE act as segregated single-molecule magnets (SMMs) displaying slow relaxation. Interestingly, upon oxidation by I₂ , the S=0 TTFTB^4- linkers of 1-RE were converted into S= 1 / 2 TTFTB^.3- radical linkers which introduced exchange-coupling between SMMs and modulated the relaxation. Furthermore, the SMM property can be restored by reduction in N,N-dimethylformamide. These results highlight the advantage of MOFs in the construction of redox-switchable SMMs.

Evaluating the crystalline orbital hierarchy and high-pressure structure–property response of an extended-ligand platinum(ii) bis(1,2-dioximato) complex

Butyl substituents enhance solution processing, but undermine the short Pt⋯Pt contacts that enable metallisation under pressure.

A Metal-Organic Framework Based on a Nickel Bis(dithiolene) Connector: Synthesis, Crystal Structure, and Application as an Electrochemical Glucose Sensor

Functionalizing the redox-active tetrathiafulvalene (TTF) core with groups capable of coordination to metals provides new perspectives on the modulation of architectures and electronic properties of organic-inorganic hybrid materials. With a view to extending this concept, we have now synthesized nickel bis(dithiolene-dibenzoic acid), [Ni(C2S2(C6H4COOH)2)2], which can be considered as the inorganic analogue of the organic tetrathiafulvalene-tetrabenzoic acid (H4TTFTB). Likewise, [Ni(C2S2(C6H4COOH)2)2] is a redox-active linker for new functional metal-organic frameworks, as demonstrated here with the synthesis of [Mn2{Ni(C2S2(C6H4COO)2)2}(H2O)2]·2DMF, (1, DMF = N,N-dimethylformamide). 1 is isomorphic to the reported [Mn2(TTFTB)(H2O)2] (2) but is a better electrochemical glucose sensor due to the multiple oxidation-reduction states of the [NiS4] core, which allow glucose to be oxidized to glucolactone by the high oxidation state [NiS4] center. As a non-enzymatic glucose sensor, 1 on Cu foam (CF), 1-CF, was synthesized by a one-step hydrothermal method and exhibited an excellent electrochemical performance. The fabricated 1-CF electrode offers a high sensitivity of 27.9 A M-1 cm-2, with a wide linear detection range from 2.0 × 10-6 to 2.0 × 10-3 M, a low detection limit of 1.0 × 10-7 M (signal/noise = 3), and satisfactory stability and reproducibility.

Conducting neutral gold bisdithiolene complex [Au(dspdt)2]˙

[Au(dspdt)2] (dspdt = 2,3-dihydro-5,6-selenophenedithiolate) is an unprecedented example of a neutral gold bisdithiolene complex with a unique structure composed of interacting dimer and trimer chains displaying relatively high electrical conductivity (0.1 S cm-1 at room temperature).

Crystal structure and metallization mechanism of the π-radical metal

Radical electrons tend to localize on individual molecules, resulting in an insulating (Mott-Hubbard) bandgap in the solid state. Herein, we report the crystal structure and intrinsic electronic properties of the first single crystal of a π-radical metal, tetrathiafulvalene-extended dicarboxylate (TED). The electrical conductivity is up to 30 000 S cm-1 at 2 K and 2300 S cm-1 at room temperature. Temperature dependence of resistivity obeys a T 3 power-law above T > 100 K, indicating a new type of metal. X-ray crystallographic analysis clarifies the planar TED molecule, with a symmetric intramolecular hydrogen bond, is stacked along longitudinal (the a-axis) and transverse (the b-axis) directions. The π-orbitals are distributed to avoid strong local interactions. First-principles electronic calculations reveal the origin of the metallization giving rise to a wide bandwidth exceeding 1 eV near the Fermi level. TED demonstrates the effect of two-dimensional stacking of π-orbitals on electron delocalization, where a high carrier mobility of 31.6 cm2 V-1 s-1 (113 K) is achieved.

Probing the structural and electronic response of Magnus green salt compounds [Pt(NH2R)4][PtCl4] (R = H, CH3) to pressure

Despite possessing the desirable crystal packing and short Pt⋯Pt stacking distances required for a large piezoresistive response, we explain why the conductivity-pressure response of the Magnus green salt [Pt(NH₃)₄][PtCl₄] is extremely sluggish.

Hydrogen bonding interactions in single component molecular conductors based on metal (Ni, Au) bis(dithiolene) complexes

Nickel (closed-shell) or gold (radical) bis(dithiolene) neutral complexes, functionalized with hydroxyethyl and thiazole moieties, afford hydrogen-bonded single component conductors.

Redox, transmetalation, and stacking properties of tetrathiafulvalene-2,3,6,7-tetrathiolate bridged tin, nickel, and palladium compounds

Here we report that capping the molecule TTFtt (TTFtt = tetrathiafulvalene-2,3,6,7-tetrathiolate) with dialkyl tin groups enables the isolation of a stable series of redox congeners and facile transmetalation to Ni and Pd. TTFtt has been proposed as an attractive building block for molecular materials for two decades as it combines the redox chemistry of TTF and dithiolene units. TTFttH₄, however, is inherently unstable and the incorporation of TTFtt units into complexes or materials typically proceeds through the in situ generation of the tetraanion TTFtt^4-. Capping of TTFtt^4- with Bu₂Sn²⁺ units dramatically improves the stability of the TTFtt moiety and furthermore enables the isolation of a redox series where the TTF core carries the formal charges of 0, +1, and +2. All of these redox congeners show efficient and clean transmetalation to Ni and Pd resulting in an analogous series of bimetallic complexes capped by 1,2-bis(diphenylphosphino)ethane (dppe) ligands. Furthermore, by using the same transmetalation method, we synthesized analogous palladium complexes capped by 1,1'-bis(diphenylphosphino)ferrocene (dppf) which had been previously reported. All of these species have been thoroughly characterized through a systematic survey of chemical and electronic properties by techniques including cyclic voltammetry (CV), ultraviolet-visible-near infrared spectroscopy (UV-vis-NIR), electron paramagnetic resonance spectroscopy (EPR), nuclear magnetic resonance spectroscopy (NMR) and X-ray diffraction (XRD). These detailed synthetic and spectroscopic studies highlight important differences between the transmetalation strategy presented here and previously reported synthetic methods for the installation of TTFtt. In addition, the utility of this stabilization strategy can be illustrated by the observation of unusual TTF radical-radical packing in the solid state and dimerization in the solution state. Theoretical calculations based on variational 2-electron reduced density matrix methods have been used to investigate these unusual interactions and illustrate fundamentally different levels of covalency and overlap depending on the orientations of the TTF cores. Taken together, this work demonstrates that tin-capped TTFtt units are ideal reagents for the installation of redox-tunable TTFtt ligands enabling the generation of entirely new geometric and electronic structures.

Binary Donor-Acceptor Adducts of Tetrathiafulvalene Donors with Cyclic Trimetallic Monovalent Coinage Metal Acceptors

Reactions between the π-acidic cyclic trimetallic coinage metal(I) complexes {[Cu(μ-3,5-(CF₃)₂pz)]₃, {[Ag(μ-3,5-(CF₃)₂pz)]₃, and {[Au(μ-3,5-(CF₃)₂pz)]₃ with TTF, DBTTF and BEDT-TTF give rise to a series of coinage metal(I)-based new binary donor-acceptor adducts {[Cu(μ-3,5-(CF₃)₂pz)]₃DBTTF} (1), {[Ag(μ-3,5-(CF₃)₂pz)]₃DBTTF} (2), {[Au(μ-3,5-(CF₃)₂pz)]₃DBTTF} (3), {[Cu(μ-3,5-(CF₃)₂pz)]₃TTF} (4), {[Ag(μ-3,5-(CF₃)₂pz)]₃TTF} (5), {[Au(μ-3,5-(CF₃)₂pz)]₃TTF} (6), {[Cu(μ-3,5-(CF₃)₂pz)]₃BEDT-TTF} (7), {[Ag(μ-3,5-(CF₃)₂pz)]₃BEDT-TTF} (8), and {[Au(μ-3,5-(CF₃)₂pz)]₃BEDT-TTF} (9), where pz = pyrazolate, TTF = tetrathiafulvalene, DBTTF = dibenzotetrathiafulvalene, and BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene. This series of binary donor-acceptor adducts has been found to exhibit remarkable supramolecular structures in both the solid state and solution, whereby they exhibit supramolecular stacked chains and oligomers, respectively. The supramolecular solid-state and solution binary donor-acceptor adducts also exhibit superior shelf stability under ambient laboratory storage conditions. Structural and other electronic properties of solids and solutions of these adducts have been characterized by single-crystal X-ray diffraction (XRD) structural analysis, ¹H and ¹⁹F NMR, UV-vis-near-IR spectroscopy, Fourier transform infrared, and computational investigations. The combined results of XRD structural data analysis, spectroscopic measurements, and theoretical studies suggest sustenance of the donor-acceptor stacked structure and electronic communication in both the solid state and solution. These properties are discussed in terms of potential applications for this new class of supramolecular binary donor-acceptor adducts in molecular electronic devices, including solar cells, magnetic switching devices, and field-effect transistors.

High Pressure Crystal Structure and Electrical Properties of a Single Component Molecular Crystal [Ni(dddt)2] (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate)

Single-component molecular conductors form an important class of materials showing exotic quantum phenomena, owing to the range of behavior they exhibit under physical stimuli. We report the effect of high pressure on the electrical properties and crystal structure of the single-component crystal [Ni(dddt)₂] (where dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate). The system is isoelectronic and isostructural with [Pd(dddt)₂], which is the first example of a single-component molecular crystal that exhibits nodal line semimetallic behavior under high pressure. Systematic high pressure four-probe electrical resistivity measurements were performed up to 21.6 GPa, using a Diamond Anvil Cell (DAC), and high pressure single crystal synchrotron X-ray diffraction was performed up to 11.2 GPa. We found that [Ni(dddt)₂] initially exhibits a decrease of resistivity upon increasing pressure but, unlike [Pd(dddt)₂], it shows pressure-independent semiconductivity above 9.5 GPa. This correlates with decreasing changes in the unit cell parameters and intermolecular interactions, most notably the π-π stacking distance within chains of [Ni(dddt)₂] molecules. Using first-principles density functional theory (DFT) calculations, based on the experimentally-determined crystal structures, we confirm that the band gap decreases with increasing pressure. Thus, we have been able to rationalize the electrical behavior of [Ni(dddt)₂] in the pressure-dependent regime, and suggest possible explanations for its pressure-independent behavior at higher pressures.

Single-component molecular conductor [Pt(dmdt)2]-a three-dimensional ambient-pressure molecular Dirac electron system

The single-component molecular conductor [Pt(dmdt)2] is a sought-after ambient-pressure molecular Dirac electron system, which exhibits a high temperature-insensitive conductivity and temperature-dependent magnetic susceptibility nearly vanishing below 120 K. First-principles DFT calculations reveal that Dirac cones emerge along the a* direction, and form Dirac nodal lines.

Effect of Substitution on the Hysteretic Phase Transition in a Bistable Phenalenyl-Based Neutral Radical Molecular Conductor

The ability to tune the physical properties of bistable organic functional materials by means of chemistry can facilitate their development for molecular electronic switching components. The butylamine-containing biphenalenyl boron neutral radical, [Bu]₂ B, crystalline compound has recently attracted significant attention by displaying a hysteretic phase transition accompanied by simultaneous bistability in magnetic, electrical, and optical properties close to room temperature. In this report, substitutional doping was applied to [Bu]₂ B by crystallizing solid solutions of bistable [Bu]₂ B and its non-radical-containing counterpart [Bu]₂ Be. With increasing doping degree, the hysteretic phase transition is gradually suppressed in terms of reducing the height, but conserves the width of the hysteresis loop as observed through magnetic susceptibility and electrical conductivity measurements. At the critical doping level of about 6 %, the abrupt transformation of the crystal structure to that of the pure [Bu]₂ Be crystal packing was observed, accompanied by a complete collapse of the hysteresis loop. Further study of the structure-properties relationships of bistable neutral radical conductors based on the [Bu]₂ B host can be conducted utilizing a variety of biphenalenyl-based molecular conductors.

Construction of three-dimensional anionic molecular frameworks based on hydrogen-bonded metal dithiolene complexes and the crystal solvent effect

Three-dimensional hydrogen-bonded anionic molecular frameworks based on a metal dithiolene complex were constructed with a significant solvent effect.

Neutral, closed-shell nickel bis(2-alkylthio-thiazole-4,5-dithiolate) complexes as single component molecular conductors

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.

Electrical Conductivity of Copper Hexamers Tuned by their Ground-State Valences

A new design concept has been realized for the construction of molecular conductors, whereby the building unit contains a core reservoir of carriers made up of metal ions with controllable valence states and shelled by flat organic ligands having an extended π-system to promote supramolecular electronic communication. Therefore, reacting the conjugated multidentate ligand 5,5'-pyridyl-3,3'-bi-1 H-pyrazole with different copper salts solvothermally led to three interesting hexameric salts having different ground-state valences, [Cu^II₆(L)₄(NO₃)(CH₃OH)₂](NO₃)₃·4CH₃OH, [(CH₃)₂NH₂][Cu^ICu^II₅(L)₄](SO₄)₂·4H₂O, and [Cu^I₂Cu^II₄(L)₄](NO₃)₂·2CH₃OH. The monovalent Cu^II₆ salt is an insulator, but the mixed-valent Cu^II₅-Cu^I and Cu^II₄-Cu^I₂ salts are semiconductors. Magnetic exchange interactions up to J_NN = -158 cm^-1 dominate the susceptibilities and lead to ground-state spin S_T = 1 (Cu^II₆), 1/2 (Cu^II₅-Cu^I), and 0 (Cu^II₄-Cu^I₂) at 40 K. Cyclic voltammetry shows the stepwise one-electron oxidation-reduction through all the possible valence states. The theoretical calculations of the electronic and band structures of the three compounds substantiate the experimentally observed physical properties.

Gold and Nickel Extended Thiophenic-TTF Bisdithiolene Complexes

Gold and nickel bisdithiolene complexes with methyl and tert-butyl substituted thiophenetetrathiafulavalenedithiolate ligands (α-mtdt and α-tbtdt) were prepared and characterized. These complexes were obtained, under anaerobic conditions, as tetrabutylammonium salts. The diamagnetic gold monoanion (n-Bu₄N)[Au(α-mtdt)₂] (3) and nickel dianionic species (n-Bu₄N)_x[Ni(α-mtdt)₂] (x = 1,2) (4) were similar to the related non-substituted extended thiophenic-TTF (TTF = tetrathiafulvalene) bisdithiolenes. However the introduction of the large, bulky substituent tert-butyl, led to the formation of a Au (I) dinuclear complex, (n-Bu₄N)₂[Au₂(α-tbtdt)₂] (5). The neutral methyl substituted gold and nickel complexes were easily obtained through air or iodine exposure as polycrystalline or amorphous fine powder. [Au(α-mtdt)₂] (6) and [Ni(α-mtdt)₂] (7) polycrystalline samples display properties of a metallic system with a room temperature electrical conductivity of 0.32 S/cm and ≈4 S/cm and a thermoelectric power of ≈5 µV/K and ≈32 µV/K, respectively. While [Au(α-mtdt)₂] (6) presented a Pauli-like magnetic susceptibility typical of conducting systems, in [Ni(α-mtdt)₂] (7) large magnetic susceptibilities indicative of high spin states were observed. Both electric transport properties and magnetic properties for gold and nickel [M(α-mtdt)₂] are indicative that these compounds are single component molecular conductors.