Neutral d8 metal bis-dithiolene complexes: Synthesis, electronic properties and applications

Structure-activity relationship of anticancer and antiplasmodial gold bis(dithiolene) complexes

Monoanionic gold bis(dithiolene) complexes were recently shown to display activity against ovarian cancer cells, Gram-positive bacteria, Candida strains and the rodent malaria parasite, P. berghei. To date, only monoanionic gold(III) bis(dithiolene) complexes with a thiazoline backbone substituted with small alkyl chains have been evaluated for biomedical applications. We now analyzed the influence of the length and the hydrophobicity vs. hydrophilicity of these complexes' alkyl chain on their anticancer and antiplasmodial properties. Isomer analogues of these monoanionic gold(III) bis(dithiolene) complexes, this time with a thiazole backbone, were also investigated in order to assess the influence of the nature of the heterocyclic ligand on their overall chemical and biological properties. In this report we present the total synthesis of four novel monoanionic gold(III) bis(dithiolene) complexes with a long alkyl chain and a polyoxygenated (PEG) chain aiming to improve their solubility and biological properties. Our results showed that the complexes with a PEG chain showed promising anticancer and antiplasmodial activities beside improved solubility, a key parameter in drug discovery and development.

A Stable Aluminum Tris(dithiolene) Triradical

A stable aluminum tris(dithiolene) triradical (3) was experimentally realized through a low-temperature reaction of the sterically demanding lithium dithiolene radical (2) with aluminum iodide. Compound 3 was characterized by single-crystal X-ray diffraction, UV-vis and EPR spectroscopy, SQUID magnetometry, and theoretical computations. The quartet ground state of triradical 3 has been unambiguously confirmed by variable-temperature continuous wave EPR experiments and SQUID magnetometry. Both SQUID magnetometry and broken-symmetry DFT computations reveal a small doublet-quartet energy gap [ΔEDQ = 0.18 kcal mol-1 (SQUID); ΔEDQ = 0.14 kcal mol-1 (DFT)]. The pulsed EPR experiment (electron spin echo envelop modulation) provides further evidence for the interaction of these dithiolene-based radicals with the central aluminum nucleus of 3.

Aliovalent Substitution Tunes Physical Properties in a Conductive Bis(dithiolene) Two-Dimensional Metal-Organic Framework

Two-dimensional conductive metal-organic frameworks have emerged as promising electronic materials for applications in (opto)electronic, thermoelectric, magnetic, electrocatalytic, and energy storage devices. Many bottom-up or postsynthetic protocols have been developed to isolate these materials or further modulate their electronic properties. However, some methodologies commonly used in classic semiconductors, notably, aliovalent substitution, are conspicuously absent. Here, we demonstrate how aliovalent Fe(III) to Ni(II) substitution enables the isolation of a Ni bis(dithiolene) material from a previously reported Fe analogue. Detailed characterization supports the idea that aliovalent substitution of Fe(III) to Ni(II) results in an in situ oxidation of the organic dithiolene linker. This substitution-induced redox tuning modulates the electronic properties in the system, leading to higher electrical conductivity and Hall mobility but slightly lower carrier densities and weaker antiferromagnetic interactions. Moreover, this aliovalent substitution improves the material's electrochemical stability and thus enables pseudocapacitive behavior in the Ni material. These results demonstrate how classic aliovalent substitution strategies in semiconductors can also be leveraged in conductive MOFs and add further support to this class of compounds as emerging electronic materials.

Redox-active ligands - a viable route to reactive main group metal compounds

Anionic redox-active ligands such as o-amidophenolates, catecholates, dithiolenes, 1,2-benzendithiolates, 2-amidobenzenethiolates, reduced α-diimines, ferrocenyl and porphyrinates are capable of reversible oxidation and thus have the ability to act as sources of electrons for metal centres. These and other non-innocent ligands have been employed in coordination complexes of base transition metals to influence their redox chemistry and afford compounds with useful catalytic, optical, magnetic and conducting properties. Despite the focus in contemporary main group chemistry on designing reactive compounds with potential catalytic activity, comparatively few studies exploring the chemistry of main group metal complexes incorporating redox-active ligands have been reported. This article highlights relevant chemical reactivity and electrochemical studies that probe the oxidation/reduction of main group metal compounds possessing redox-active ligands and comments on the prospects for this relatively untapped avenue of research.

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).

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.

Neutral Antiaromatic Bis(1,2-dithiolene)-Chelated Nickel Complexes Bearing Multiradical Characters

Metal-organic complexes with radical characteristics are unique species attracting immense attention in recent years due to their peculiar properties and promising applicability in a wide variety of innovative research fields. However, the reported complexes typically do not exceed diradicality. This study systematically investigates a series of square planar neutral Ni-bis(1,2-dithiolene) and Ni-bis(1,2-dioxolene) complexes with linear, branched, and macrocyclic configurations via ab initio calculations. The linear Ni-complexes display strong singlet diradical characters, while their branched counterparts can also exhibit moderate singlet multiradical characters. Importantly, the macrocyclic Ni-complexes can possess extremely strong singlet multiradical characters up to dodeca-radicality along with their global antiaromaticity and hence strong induced ring current in the presence of an external magnetic field, ascribed to the localization of unpaired α and β electrons residing in the highest few molecular orbitals at different molecular sites, minimizing their coupling and annihilation. Our work represents the first indication in the rational design of novel multiradical neutral antiaromatic macrocyclic complexes for potential applications in molecular machines and electronic devices.

Cooperative redox and spin activity from three redox congeners of sulfur-bridged iron nitrosyl and nickel dithiolene complexes

The synthesis of sulfur-bridged Fe-Ni heterobimetallics was inspired by Nature's strategies to "trick" abundant first row transition metals into enabling 2-electron processes: redox-active ligands (including pendant iron-sulfur clusters) and proximal metals. Our design to have redox-active ligands on each metal, NO on iron and dithiolene on nickel, resulted in the observation of unexpectedly intricate physical properties. The metallodithiolate, (NO)Fe(N2S2), reacts with a labile ligand derivative of [NiII(S2C2Ph2)]0, NiDT, yielding the expected S-bridged neutral adduct, FeNi, containing a doublet {Fe(NO)}7. Good reversibility of two redox events of FeNi led to isolation of reduced and oxidized congeners. Characterization by various spectroscopies and single-crystal X-ray diffraction concluded that reduction of the FeNi parent yielded [FeNi]-, a rare example of a high-spin {Fe(NO)}8, described as linear FeII(NO-). Mössbauer data is diagnostic for the redox change at the {Fe(NO)}7/8 site. Oxidation of FeNi generated the 2[FeNi]+⇌[Fe2Ni2]2+ equilibrium in solution; crystallization yields only the [Fe2Ni2]2+ dimer, isolated as PF6- and BArF- salts. The monomer is a spin-coupled diradical between {Fe(NO)}7 and NiDT+, while dimerization couples the two NiDT+ via a Ni2S2 rhomb. Magnetic susceptibility studies on the dimer found a singlet ground state with a thermally accessible triplet excited state responsible for the magnetism at 300 K (χMT = 0.67 emu·K·mol-1, µeff = 2.31 µB), and detectable by parallel-mode EPR spectroscopy at 20 to 50 K. A theoretical model built on an H4 chain explains this unexpected low energy triplet state arising from a combination of anti- and ferromagnetic coupling of a four-radical molecular conglomerate.

A Mesoionic Diselenolene Anion and the Corresponding Radical Dianion

Dichalcogenolenes are archetypal redox non-innocent ligands with numerous applications. Herein, a diselenolene ligand with fundamentally different electronic properties is described. A mesoionic diselenolene was prepared by selenation of a C2-protected imidazolium salt. This ligand is diamagnetic, which is in contrast to the paramagnetic nature of standard dichalcogenolene monoanions. The new ligand is also redox-active, as demonstrated by isolation of a stable diselenolene radical dianion. The unique electronic properties of the new ligand give rise to unusual coordination chemistry. Thus, preparation of a hexacoordinate aluminum tris(diselenolene) complex and a Lewis acidic aluminate complex with two ligand-centered unpaired electrons was achieved.

Mesoionic Dithiolates (MIDts) Derived from 1,3-Imidazole-Based Anionic Dicarbenes (ADCs)

Mesoionic dithiolates [(MIDtAr )Li(LiBr)2 (THF)3 ] (MIDtAr ={SC(NDipp)}2 CAr; Dipp=2,6-iPr2 C6 H3 ; Ar=Ph 3 a, 3-MeC6 H4 (3-Tol) 3 b, 4-Me2 NC6 H4 (DMP) 3 c) and [(MIDtPh )Li(THF)2 ] (4) are readily accessible (in≥90 % yields) as crystalline solids on treatments of anionic dicarbenes Li(ADCAr ) (2 a-c) (ADCAr ={C(NDipp)2 }2 CAr) with elemental sulfur. 3 a-c and 4 are monoanionic ditopic ligands with both the sulfur atoms formally negatively charged, while the 1,3-imidazole unit bears a formal positive charge. Treatment of 4 with (L)GeCl2 (L=1,4-dioxane) affords the germylene (MIDtPh )GeCl (5) featuring a three-coordinated Ge atom. 5 reacts with (L)GeCl2 to give the Ge-Ge catenation product (MIDtPh )GeGeCl3 (6). KC8 reduction of 5 yields the homoleptic germylene (MIDtPh )2 Ge (7). Compounds 3 a-c and 4-7 have been characterized by spectroscopic studies and single-crystal X-ray diffraction. The electronic structures of 4-7 have been analyzed by DFT calculations.

Carbene-Stabilized Dithiolene (L0 ) Zwitterions

A series of reactions between Lewis bases and an imidazole-based dithione dimer (1) has been investigated. Both cyclic(alkyl)(amino)carbene (CAAC) (2) and N-heterocyclic carbene (NHC) (4), in addition to N-heterocyclic silylene (NHSi) (6), demonstrate the capability to cleave the sulphur-sulphur bonds in 1, giving carbene-stabilized dithiolene (L⁰ ) zwitterions (3 and 5) and a spirocyclic silicon-dithiolene compound (7), respectively. The bonding nature of 3, 5, and 7 are probed by both experimental and theoretical methods.

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.

Platinum diimine-dithiolate complexes as a new class of photoconducting compounds for pristine photodetectors: case study on [Pt(bipy)(Naph-edt)] (bipy = 2,2'-bipyridine; Naph-edt2- = 2-naphthylethylene-1,2-dithiolate)

The photoconducting properties of platinum diimine-dithiolate complex [Pt(bipy)(Naph-edt)] (1; bipy = 2,2'-bipyridine; Naph-edt2- = 2-naphthylethylene-1,2-dithiolate) were investigated. DFT calculations on a model assembly with four complex units suggest that the high external quantum efficency measured on a prototype photodetector correlates with the intermolecular character of electronic excitations in the visible region.

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.

Magnetostructural relationships in [Ni(dmit)2]- radical anions

This work explores the relationship between the magnetic properties of salts based on [Ni(dmit)2]- radicals and different arrangements that these radicals can adopt in the crystals, induced by the packing constrains imposed by the counterions. Our analysis is based on difference dedicated configuration interaction calculations on models containing two neighbouring [Ni(dmit)2]- units with different interaction patterns. The amplitude and sign of these through-space interactions can be rationalized on the basis of a valence-only model that essentially analyzes the effective interactions between the atoms carrying the electronic density of singly occupied orbitals (SOMOs). Despite the simplicity of the model, it provides simple rules to predict the nature and the expected amplitude (strong/medium/weak) of the leading interactions in systems based on these [Ni(dmit)2]- radicals.

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.

Carbene-mediated synthesis of a germanium tris(dithiolene)dianion

While the 1 : 1 reaction of 3 with an N-heterocyclic carbene ({(Me)CN(i-Pr)}2C:) in THF resulted in ligand-substituted product 4, the corresponding 1 : 2 reaction (in the presence of H2O) gives the first structurally characterized germanium tris(dithiolene)dianion 5 as the major product and the "naked" dithiolene radical 6˙ as a minor by-product. The structure and bonding of 4 and 5 were probed by experimental and theoretical methods. Our study suggests that carbene-mediated partial hydrolysis may represent a new method to access tris(dithiolene) complexes of main-group elements.

Pseudo-octahedral nickel(ii) complexes of strongly absorbing benzannulated pincer-type amido ligands: ligand-based redox and non-Aufbau electronic behaviour

The synthesis, structures and electronic characterization of three strongly coloured, pseudo-octahedral Ni(ii) complexes supported by redox-active diarylamido ligands featuring benzannulated N-heterocyclic donor arms are reported. The S = 1 paramagnets each present two singly occupied molecular orbitals (SOMOs) identified as metal-based by density functional theory (DFT), consistent with solid-state and solution magnetism measurements. Upon applying oxidative potentials, non-Aufbau behaviour leads to the appearance of intense and well-defined absorption features extending into the near IR (NIR). The attribution of these features to the onset of aminyl radical character through ligand-based redox is corroborated by exceptionally strong intervalence charge-transfer (IVCT) transitions ascribed to electronic communication between two Namido moieties across a Ni(ii) bridge.

Magnetism, dielectrics and ion conduction in two polymorphs of a heteroleptic bis(dithiolato)nickelate molecular solid

A new heteroleptic compound [triethylpropylammonium][Ni(dmit)(mnt)] with two crystal polymorphs, which show different magnetic and dielectric properties, has been reported.

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.

Prototype Material for New Strategy of Photon Energy Storage

The smart utilization of photons is paid global attention from the viewpoint of renewable energy and information technology. However, it is still impossible to store photons as batteries and condensers do for electrons. All the present technologies utilize (the energy of) photons in situ, such as solar panels, or in spontaneous relaxation processes, such as photoluminescence. If we can store the energy of photons over an arbitrary period and utilize them on demand, not only we will make an innovative progress in energy management, but we will also be able to replace a part of electrons by photons in the information technology for more efficient performance. In this article, we review a prototype of such a material including the current status of related research as well as where we are heading for.

Design Strategies of Photoacoustic Molecular Probes

Photoacoustic (PA) probes have been developed very quickly and applied in broad areas in recent years. Most of them are constructed based on organic dyes with intrinsic near-infrared (NIR) absorption properties. To increase PA contrast and improve imaging resolution and the sensitivity of detection, various methods for the design of PA probes have been developed. This minireview mainly focuses on the development and design strategies of activatable small-molecule PA probes in four aspects: reaction-cleavage, metal ion chelation, photoswitch, and protonation-deprotonation. It highlights some key points of designing PA probes corresponding to their properties and applications. The challenges and perspectives for small-molecule PA probes are also discussed.

Carbene-Stabilized Disilicon as a Silicon-Transfer Agent: Synthesis of a Dianionic Silicon Tris(dithiolene) Complex

Reaction of carbene-stabilized disilicon (1) with the lithium-based dithiolene radical (2^. ) affords the first dianionic silicon tris(dithiolene) complex (3). Notably, the formation of 3 represents the unprecedented utilization of carbene-stabilized disilicon (1) as a silicon-transfer agent. The nature of 3 was probed by multinuclear NMR spectroscopy, single-crystal X-ray diffraction, and DFT computations.

Series of Near-IR-Absorbing Transition Metal Complexes with Redox Active Ligands

New soluble and intensely near-IR-absorbing transition metal (Ti, Zr, V, Ni) complexes were synthesized using a redox non-innocent N,N'-bis(3,5-di-tertbutyl-2-hydroxy-phenyl) -1,2-phenylenediamine (H4L) as a ligand precursor. In all the complexes, ([Ti(Lox)2, [Zr(Lox)2], [V(Lsq1)(HLox)] and [Ni(HLox)2], two organic molecules coordinate to the metal center as tri- or tetradentate ligands. The solid-state structures of the complexes were determined using single crystal XRD, and the compounds were further characterized with Electrospray Ionisation Mass Spectrometry (ESI-MS). Thermoanalytical measurements indicated the thermal stabilities of the complexes. All compounds absorb strongly in the near-IR region and show very interesting magnetic and electrochemical properties. Moreover, it was shown that the V and Ni complexes can also convert absorbed near-IR photons to (un)paired electrons, which indicates great promise in photovoltaic applications.

Structural Study of the Compounds Formed in the Reactions of FeCl3·6H2O with Ni(OH)2 in the Presence of Dithiolenes HSRSH (R = C6H2Cl2 or C6H4)

In our attempts to prepare coordination polymers by reaction of FeCl₃·6H₂O and Ni(OH)₂ in the presence of dithiolenes HSC₆H₂X₂SH (X = Cl or H), several ion pairs of compounds containing the anionic entity [Ni(SC₆H₂X₂S)₂]⁻ were obtained instead. It was also found that other species without dithiolene ligands were formed in these reactions, giving rise to different ion pairs and a tetrametallic cluster. The careful isolation of the different types of crystalline solids allowed the characterization of all of the resulting compounds by single crystal X-ray diffraction (SCXRD). In order to establish the amount of nickel and iron present in the crystals, complementary total reflection X-ray fluorescence (TXRF) analyses were performed. The eight different structural types that were obtained are described and compared with related ones found in the literature.

Photoconducting Devices with Response in the Visible-Near-Infrared Region Based on Neutral Ni Complexes of Aryl-1,2-dithiolene Ligands

Metal bis(1,2-dithiolene) complexes belonging to the class [Ni(Ar-edt)₂]^x- [Ar-edt^2- = arylethylene-1,2-dithiolate; Ar = phenyl, (1^x-), 2-naphthyl (2^x-); x = 0 and 1] were fully characterized by NMR, UV-visible-near-infrared (UV-vis-NIR), diffuse reflectance, and FT-IR spectroscopy, as well as cyclic voltammetry and single-crystal X-ray diffraction analysis. These complexes have emerged as new photoconducting materials that allowed for the development of a prototype of photodetectors with response in the vis-NIR region. The photodetecting devices showed in some cases quantum efficiencies orders of magnitude higher than those of previously reported 1,2-dithiolene systems.

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.

A molecular crystal with an unprecedentedly long-lived photoexcited state

The Au(iii)-complex anions in a newly synthesised compound BPY[Au(dmit)₂]₂ (BPY = N,N'-ethylene-2,2'-bipyridinium, dmit = 1,3-dithiole-2-thione-4,5-dithiolate) reversibly exhibit a molecular distortion in the solid state under UV-radiation. The photoexcited state is maintained for a week at 298 K, during which time molecules relax to their original structures and energy is gradually released as heat without decomposition or light emission. Most Au atoms adopt square planar (SP) coordination geometries, but some anions have unusual non-planar (NP) coordination geometries that produce disorder at the Au sites. The total (Gibbs) energy of the system depends on the proportion of Au atoms of NP geometry, which is directly determined from the occupancy (Occ (%)) by X-ray diffractometry. Due to phase transition, Occ substantially changes at a critical temperature (T_C) of ∼280 K without other structural changes; however it remains almost constant in each phase. In addition, due to UV-promoted charge-transfer transitions between BPY and Au(dmit)₂, Occ can be controlled by UV irradiation (∼250-450 nm). The UV-excited states have unprecedentedly long relaxation times (t_1/2 > 36 h at 298 K), which is attributed to the close connection between the degrees of freedom on charge, spin, and molecular structures.

Lewis base-complexed magnesium dithiolenes

The first magnesium-based dithiolene, 2, was prepared by reaction of the lithium dithiolene radical, 1˙, with 2-mesitylmagnesium bromide. Reaction of 2 with N-heterocyclic carbenes (in toluene) gave a carbene-stabilized magnesium monodithiolene complex, 3. Complex 3, in turn, is readily converted to a THF-solvated magnesium bis-dithiolene dianion, 4, via partial hydrolysis in polar solvents (i.e., THF/CH3CN). Compounds 2, 3 and 4 have been spectroscopically and structurally characterized and probed by DFT computations.

Copper dithiolene [Cu(SC6H2Cl2S)2]− units connected to alkaline/copper complexes: from ionic assemblies to discrete molecular entities and coordination polymers

New coordination polymers or ion-pair complexes containing the [Cu(SC₆H₂Cl₂S)₂]⁻ entity and M⁺ (alkaline or Cu metals) has been obtained.

Synthesis and structural characterization of transition metal dithiolene derivatives containing divalent metals as counter-cations

Complexes containing [Fe₂(SC₆H₂Cl₂S)₄]²⁻ or [Ni(SC₆H₂Cl₂S)₂]⁻ entities and divalent metal cations as well as an 1D-coordination polymer K/Zn have been obtained and their magnetic behaviour studied.

Redox chemistry of an anionic dithiolene radical

The redox reactivity of a stable anionic dithiolene radical has been explored, giving the corresponding dithiolate and neutral dithiolene dimers.

Theoretical study of the photoconduction and photomagnetism of the BPY[Ni(dmit)2]2 molecular crystal

UV-Vis light generates photoexcited (BPY²⁺)* radicals that interact with the close Ni(dmit)₂ units, modifying their magnetic and conducting properties.

Stable Boron Dithiolene Radicals

Whereas low-temperature (-78 °C) reaction of the lithium dithiolene radical 1^. with boron bromide gives the dibromoboron dithiolene radical 2^. , the parallel reaction of 1^. with (C₆ H₁₁ )₂ BCl (0 °C) affords the dicyclohexylboron dithiolene radical 3^. . Radicals 2^. and 3^. were characterized by single-crystal X-ray diffraction, UV/Vis, and EPR spectroscopy. The nature of these radicals was also probed computationally. Under mild conditions, 3^. undergoes unexpected thiourea-mediated B-C bond activation to give zwitterion 4, which may be regarded as an anionic dithiolene-modified carbene complex of the sulfenyl cation RS⁺ (R=cyclohexyl).

Cobalt complexes with redox-active anthraquinone-type ligands

Three anthraquinone-type multidentate ligands, HL1-3 (HL = 2-R-1H-anthra[1,2-d]imidazole-6,11-dione; HL1: R = (2-pyridyl), HL2; R = (4,6-dimethyl-2-pyridyl), HL3; R = (6-methoxy-2-pyridyl)), were prepared, and their complexation behaviour was investigated. Three bis-chelate cobalt complexes with the formula [CoII(L1-3)2]·n(solv.) (1, 2, and 3 for HL1, HL2, and HL3, respectively), in which the ligands adopted tridentate binding modes, were synthesized and structurally characterized by single-crystal X-ray analyses. Electrochemical studies of 1-3 in CH2Cl2 reveal three reversible redox waves, assigned to ligand and cobalt-centred processes. Additional complexes were obtained in which HL1 adopted a bidentate binding mode, stabilising the mono-chelate [CoII(HL1)(NO3)2(DMF)2] (4) species and tris-chelate [CoIII(L1)3] (5) complex in which the cobalt ion was in its 3+ state. The electrochemical properties of complex 5 were investigated in DMF, and the Co(ii)/Co(iii) redox couple was found to be negatively shifted compared to that of complex 1, while the ligand-based processes became irreversible. Tridentate chelation is found to stabilise the anthraquinone ligands and unlocks their redox multi-stability.

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.