Neutral Metal 1,2-Dithiolenes: Preparations, Properties and Possible Applications of Unsymmetrical in Comparison to the Symmetrical

Macroscopic Structural Transition of Nickel Dithiolate Capsule with Uniaxial Magnetic Anisotropy in Water

Meeting the Internet of Things (IoT) demand for flexible organic spintronics requires dynamically flexible, "soft" organic magnetic materials. These materials should be capable of reordering their macroscopic assemblies in response to external stimuli. Unlike conventional rigid, "hard" crystalline organic paramagnets, that are typically composed of open-shell π- or d/π-conjugated planar molecules and rely on intermolecular interactions in the ordered, assembled structures, soft paramagnets necessitate a delicate balance between long-range structural order (essential for controlling magnetic properties) and dynamic flexibility a challenge previously unmet for open-shell planar molecules. In this study, an amphiphilic d/π-conjugated nickel dithiolate radical anion salt is presented that self-assembles into ordered membranes, forming capsule-like macrostructures with exceptional stability in aqueous environments. This design achieves the desired balance. These assemblies exhibit uniaxial magnetic anisotropy driven by significant spin-spin interactions and undergo temperature-dependent macroscopic structural transitions representing, to the knowledge, the first observation of such behavior for assemblies of open-shell planar molecules. This well-defined, single-molecular-weight system provides critical structural and mechanism insights for soft matter design and a versatile platform for spintronic applications. The findings advance the development of flexible, tunable molecular soft paramagnets, expanding their potential for innovative applications in flexible devices and beyond.

Enantiomorphic single component conducting nickel(II) and platinum(II) bis(diethyl-dddt) crystalline complexes

Monoanionic and neutral nickel(II) and platinum(II) bis(dithiolene) complexes based on the 5,6-diethyl-5,6-dihydro-1,4-dithiin-2,3-dithiolate (de-dddt) chiral ligand have been prepared in racemic and enantiopure forms. Neutral closed-shell species have been generated from monoanionic precursors upon electrocrystallization. The racemic anionic (TBA)[Ni(S,S-de-dddt)(R,R-de-dddt)] complex crystallized in the centrosymmetric space group P21/c, while the neutral complexes crystallized in the enantiomorphic tetragonal space group P41212 or P43212. Very subtle conformational differences concerning the orientation of the ethyl substituents are observed between the racemic and the enantiopure compounds, thus impacting the intermolecular interactions at the nanoscale level. Indeed, in the former, the ethyl substituents are all-axial in both independent complexes, while in the latter, one of the independent complexes shows a mixed (eq, eq, ax, ax) conformation and the other independent complex of the asymmetric unit shows the all-axial conformation. Such a tenuous difference at the molecular/nanoscale level strongly impacts the conductivity of the materials. Temperature dependent high pressure single crystal conductivity measurements show activated conductivity for all the materials, with room temperature conductivity values of up to 1.3 × 10-3 S cm-1 for [Ni(S,S-de-dddt)2] at 12.3 GPa and 3.0 × 10-4 S cm-1 for [Pt(R,R-de-dddt)2] at 12.9 GPa. Nevertheless, the racemic compounds are more conductive, i.e. 3.8 × 10-2 S cm-1 for [Ni(rac-de-dddt)2] at 10.0 GPa and 1.5 × 10-3 S cm-1 for [Pt(rac-de-dddt)2] at 10.5 GPa, in agreement with the shorter and more numerous S⋯S intermolecular contacts observed in the crystal structures of the racemic complexes. Moreover, a detailed analysis of DFT calculations suggests that smaller band gaps and higher conductivities should occur for the racemic solids and for the Pt versus Ni complexes.

Mixed-Valence Conductors from Ni Bis(diselenolene) Complexes with a Thiazoline Backbone

Highly conducting, mixed-valence, multi-component nickel bis(diselenolene) salts were obtained by electrocrystallization of the monoanionic species [Ni(Me-thiazds)₂]^-1 (Me-thiazds: N-methyl-1,3-thiazoline-2-thione-4,5-diselenolate), with 1:2 and 1:3 stoichiometries depending of the counter ion used (Et₄N⁺ and nBu₄N⁺ vs Ph₄P⁺, respectively). This behavior strongly differs from that of the corresponding monoanionic dithiolene complexes whose oxidation afforded the single component neutral species. This provides additional rare examples of mixed-valence conducting salts of nickel diselenolene complexes, only known in two examples with the dsit (1,3-dithiole-2-thione-4,5-diselenolate) and dsise (1,3-dithiole-2-selone-4,5-diselenolate) ligands. The mixed-valence salts form highly dimerized or trimerized bi- and trimetallic units, rarely seen with such nickel complexes. Transport measurements under a high pressure (up to 10 GPa) and band structure calculations confirm the semiconducting character of [Ph₄P][Ni(Me-thiazds)₂]₃ and the quasi metallic character of [Et₄N][Ni(Me-thiazds)₂]₂ and [NBu₄]_x[Ni(Me-thiazds)₂]₂ salts (0 < x < 1).

Ambipolar Nickel Dithiolene Complex Semiconductors: From One- to Two-Dimensional Electronic Structures Based upon Alkoxy Chain Lengths

Air-stable single-component ambipolar organic semiconductors that conduct both holes and electrons are highly desired but have been rarely realized. Neutral nickel bis(dithiolene) complexes are promising candidates that fulfill the stringent electronic requirements of shallow HOMO levels and deep LUMO levels, which can reduce the carrier injection barrier to overcome the work function of gold electrodes and ensure air stability. However, most nickel bis(dithiolene) analogs that have been characterized as ambipolar semiconductors have twisted molecular structures that hinder the effective intermolecular interactions required for carrier conduction. To address this issue, we synthesized planar alkoxy-substituted nickel bis(dithiolene) analogs that facilitate dense packing with effective intermolecular interactions. Remarkably, changing the methoxy substituents to ethoxy or propoxy groups led to a dramatic change in the packing mode, from one-dimensional to herringbone-like, while maintaining effective intermolecular interactions. These materials overcome the usual trade-off between crystallinity and solubility; they are highly crystalline, even in their film forms, and are highly soluble in organic solvents. They are therefore readily solution-processable to form semiconducting layers with well-defined and well-ordered structures in field-effect transistors. Devices based on these compounds exhibited efficient ambipolar characteristics, even after several months of exposure to air, achieving high carrier mobilities of up to 10^-2 cm² V^-1 s^-1 and large on/off ratios of up to 10⁵, which are the top-class performances achieved for a single-component ambipolar semiconductor material driven in air.

Electronic structure and magnetic properties of transition metal Kagome metal-organic frameworks

Kagome metal-organic frameworks (MOFs) are considered a new class of materials that can host two-dimensional (2D) magnetism and correlated electron phenomena such as superconductivity and quantum anomalous Hall effect. Despite...

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.

Tunable NIR Absorption Property of a Dithiolene Nickel Complex: A Promising NIR-II Absorption Material for Photothermal Therapy

Exogenous photothermal agents absorbing in the second near-infrared optical window (NIR-II, 1000-1700 nm) have received much attention due to their use in noninvasive photothermal therapy. A small quantity of organic NIR-II photothermal agents have been exploited, and the development of organic NIR-II photothermal materials is an urgent need for biological applications. In this study, we designed and synthesized three dithiolene nickel(II) complexes with different ligands-bis(phenyl) dithiolene for NiBD-Ph, bis(fluorenyl) dithiolene for NiBD-Fl, and bis(carbazolyl) dithiolene for NiBD-Cz-and investigated their photophysical properties. These complexes exhibited ligand-dependent NIR absorption performance, centered at 854 nm for NiBD-Ph, 942 nm for NiBD-Fl, and 1010 nm for NiBD-Cz, respectively. NiBD-Cz is wrapped in ethylene oxide/propylene oxide block copolymer (F-127) through a hydrophilic-hydrophobic interaction to form water-soluble NiBD-Cz/F-127 nanoparticles (NiBD-Cz NPs), and the absorption peak of NiBD-Cz NPs are red-shifted to 1036 nm. NiBD-Cz NPs exhibit good dispersibility in water, robust photostability, and a high photothermal conversion efficiency (PCE) of 63.6% under 1064 nm laser irradiation, which is the highest PCE among metal bis(dithiolene) complexes up to now. The high PCE makes it possible to achieve better photothermal treatment effects even at low concentrations and under low-power laser irradiation.

Diradical Character of Neutral Heteroleptic Bis(1,2-dithiolene) Metal Complexes: Case Study of [Pd(Me2timdt)(mnt)] (Me2timdt = 1,3-Dimethyl-2,4,5-trithioxoimidazolidine; mnt2- = 1,2-Dicyano-1,2-ethylenedithiolate)

The reaction of the bis(1,2-dithiolene) complex [Pd(Me₂timdt)₂] (1; Me₂timdt^•– = monoreduced 1,3-dimethyl-2,4,5-trithioxoimidazolidine) with Br₂ yielded the complex [Pd(Me₂timdt)Br₂] (2), which was reacted with Na₂mnt (mnt^2– = 1,2-dicyano-1,2-ethylenedithiolate) to give the neutral mixed-ligand complex [Pd(Me₂timdt)(mnt)] (3). Complex 3 shows an intense solvatochromic near-infrared (NIR) absorption band falling between 955 nm in DMF and 1060 nm in CHCl₃ (ε = 10700 M^–1 cm^–1 in CHCl₃). DFT calculations were used to elucidate the electronic structure of complex 3 and to compare it with those of the corresponding homoleptic complexes 1 and [Pd(mnt)₂] (4). An in-depth comparison of calculated and experimental structural and vis–NIR spectroscopic properties, supported by IEF-PCM TD-DFT and NBO calculations, clearly points to a description of 3 as a dithione-dithiolato complex. For the first time, a broken-symmetry (BS) procedure for the evaluation of the singlet diradical character (DC) of heteroleptic bis(1,2-dithiolene) complexes has been developed and applied to complex 3. The DC, predominant for 1 (n_DC = 55.4%), provides a remarkable contribution to the electronic structures of the ground states of both 3 and 4, showing a diradicaloid nature (n_DC = 24.9% and 27.5%, respectively). The computational approach developed here clearly shows that a rational design of the DC of bis(1,2-ditiolene) metal complexes, and hence their linear and nonlinear optical properties, can be achieved by a proper choice of the 1,2-dithiolene ligands based on their electronic structure.

The reaction of [Pd(Me₂timdt)₂] (1; Me₂timdt^•− = monoreduced 1,3-dimethyl-2,4,5-trithioxoimidazolidine) with Br₂ yielded [Pd(Me₂timdt)Br₂] (2), which was reacted with Na₂mnt (mnt²⁻ = 1,2-dicyano-1,2-ethylenedithiolate) to give [Pd(Me₂timdt)(mnt)] (3), showing an intense solvatochromic near-infrared (NIR) absorption band. The singlet diradical character (DC), predominant for 1, provides a remarkable contribution to the ground states of 3 and 4. A rational design of the DC of bis(1,2-dithiolene) complexes can be achieved by a proper choice of the 1,2-dithiolene ligands.

Electrochemical deposition of a semiconducting gold dithiolene complex with NIR absorption

Here, the synthesis of a new anionic gold dithiolene complex, NBu₄·[1-i], and that of its corresponding neutral gold complex 2 is reported. Complex 2 shows strong absorption into the IR, semiconductivity (σ_RT = 3.06 × 10^-7 S cm^-1) with an activation energy of 0.25 eV, and weakly temperature dependent paramagnetic susceptibility, indicating strong intermolecular interactions in the solid state. As a consequence of their strong intermolecular interactions, neutral gold dithiolene complexes are often highly insoluble, limiting their utility and processability. Electrochemical deposition is used to deposit conductive films of complex 2, which retain the NIR properties present in the bulk material, indicting that the strong intermolecular interactions are retained in the film.

A Mixed-Valence Tetra-Nuclear Nickel Dithiolene Complex: Synthesis, Crystal Structure, and the Lability of Its Nickel Sulfur Bonds

In this study, by employing a common synthetic protocol, an unusual and unexpected tetra-nuclear nickel dithiolene complex was obtained. The synthesis of the [Ni4(ecpdt)6]2− dianion (ecpdt = (Z)-3-ethoxy-3-oxo-1-phenylprop-1-ene-1,2-bis-thiolate) with two K+ as counter ions was then intentionally reproduced. The formation of this specific complex is attributed to the distinct dithiolene precursor used and the combination with the then coordinated counter ion in the molecular solid-state structure, as determined by X-ray diffraction. K2[Ni4(ecpdt)6] was further characterized by ESI-MS, FT-IR, UV-Vis, and cyclic voltammetry. The tetra-nuclear complex was found to have an uncommon geometry arising from the combination of four nickel centers and six dithiolene ligands. In the center of the arrangement, suspiciously long Ni–S distances were found, suggesting that the tetrameric structure can be easily split into two identical dimeric fragments or two distinct groups of monomeric fragments, for instance, upon dissolving. A proposed variable magnetism in the solid-state and in solution due to the postulated dissociation was confirmed. The Ni–S bonds of the “inner” and “outer” nickel centers differed concurrently with their coordination geometries. This observation also correlates with the fact that the complex bears two anionic charges requiring the four nickel centers to be present in two distinct oxidation states (2 × +2 and 2 × +3), i.e., to be hetero-valent. The different coordination geometries observed, together with the magnetic investigation, allowed the square planar “outer” geometry to be assigned to d8 centers, i.e., Ni2+, while the Ni3+ centers (d7) were in a square pyramidal geometry with longer Ni–S distances due to the increased number of donor atoms and interactions.

Strategic design of thiophene-fused nickel dithiolene derivatives for efficient NLO response

The zwitterionic donor–acceptor group significantly reduces the HOMO–LUMO energy gap resulting in an enormous increase in the first hyperpolarizability values.

Fluorination induced electronic effects on a Pt(ii) square-planar complex of the o-phenylenediimine ligand

The effect induced by the fluorine atoms on a Pt(ii) complex of the tetrafluorinated-1,2-phenylenediimine ligand is highlighted by comparison with the corresponding Ni(ii) and Pt(ii) hydrogenated complexes.

Experimental and Theoretical Insight into Electrocatalytic Hydrogen Evolution with Nickel Bis(aryldithiolene) Complexes as Catalysts

A series of neutral and monoanionic nickel dithiolene complexes with p-methoxyphenyl-substituted 1,2-dithiolene ligands have been prepared and characterized with physicochemical methods. Two of the complexes, the monoanion of the symmetric [Ni{S2C2(Ph-p-OCH3)2}2] (3(-)) with NBu4(+) as a counterion and the neutral asymmetric [Ni{S2C2(Ph)(Ph-p-OCH3)}2] (2), have been structurally characterized by single-crystal X-ray crystallography. All complexes have been employed as proton-reducing catalysts in N,N-dimethylformamide with trifluoroacetic acid as the proton source. The complexes are active catalysts with good faradaic yields, reaching 83% for 2 but relatively high overpotential requirements (0.91 and 1.55 V measured at the middle of the catalytic wave for two processes observed depending on the different routes of the mechanism). The similarity of the experimental data regardless of whether the neutral or anionic form of the complexes is used indicates that the neutral form acts as a precatalyst. On the basis of detailed density functional theory calculations, the proposed mechanism reveals two different main routes after protonation of the dianion of the catalyst in accordance with the experimental data, indicating the role of the concentration of the acid and the influence of the methoxy groups. Protonation at sulfur seems be more favorable than that at the metal, which is in marked contrast with the catalytic mechanism proposed for analogous cobalt dithiolene complexes.

Chiral, radical, gold bis(dithiolene) complexes

Chiral gold(iii) dithiolene complexes are investigated for further oxidation to the neutral radical species, as potential single component conductors.

Structure-dependent electronic transition in a new type of π-electron delocalized multi-sulfur bis(dithiolene)nickel complex

Four new nickel bis(dithiolene) complexes were synthesized and characterized. The UV-vis-NIR spectra and DFT calculations indicate that their HOMO and LUMO energy levels are highly depended on the donating/withdrawing abilities of their substituents.

Zn(ii) and Cu(ii) complexes of a new thiophene-based salphen-type ligand: solution-processable high-performance field-effect transistor materials

Organic field-effect transistor (OFET) devices based on solution-processed Cu(ii) and Zn(ii) complexes of a new thiophene-based salphen-type ligand exhibited high p-type mobilities (up to 1.5 cm²V⁻¹s⁻¹).