Square-planar d8 metal mixed-ligand dithiolene complexes as second order nonlinear optical chromophores: Structure/property relationship

Mixed-ligand, radical, gold bis(dithiolene) complexes: from single-component conductors to controllable NIR-II absorbers

Neutral radical bis(dithiolene) gold complexes [Au(dt)2]˙ are known to exhibit a strong absorption in the 1400-2000 nm NIR absorption range. Here, we demonstrate that the NIR signature of mixed-ligand bis(dithiolene) gold complexes [Au(dtA)(dtD)]˙ associating two different dithiolene, dtA and dtD, is found at higher energy, out of the range of the homoleptic analogs [Au(dtA)2]˙ and [Au(dtD)2]˙, in the looked-after NIR-II 1000-1400 nm absorption range. An efficient synthetic approach towards precursor mixed-ligand monoanionic gold bis(dithiolene) complexes [Au(dtA)(dtD)]-1 is reported. Using this strategy, no symmetrical complexes are formed and, upon electrocrystallization, no scrambling was observed in solution, allowing for the isolation of radical gold bis(dithiolene) complex such as [Au(bdt)(Et-thiazdt)]˙ (bdt: benzene-1,2-dithiolate; Et-thiazdt: N-ethyl-thiazoline-2-thione-3,4-dithiolate), which behaves as a single-component conductor. It is shown from theoretical calculations that the spin polarization induced by electron repulsions leads to a strong localization of the spin-orbitals, and provides a sound basis to understand, (i) the different ligand-based oxidation potentials, (ii) the NIR optical absorption at notably higher energies and (iii) the larger potential difference of the two redox processes than in the parent symmetric complexes. The solid-state properties of the radical complex [Au(bdt)(Et-thiazdt)]˙ are the consequence of a strongly 1D electronic structure with weakly dimerized chains and electronic localization favoring a semiconducting behavior, stable under pressures up to 18.2 GPa. Altogether, the versatility of the preparation method of [Au(dtA)(dtD)]-1 salts opens the route for a wide library of different mixed-ligand radical complexes [Au(dtA)(dtD)]˙ with simultaneously an adaptable absorption in the NIR-II range and the rich structural chemistry of single-component conductors.

Near-IR Absorbers Based on Pt(II)-Dithiolene Donor–Acceptor Charge-Transfer (CT) Systems: A Structural Analysis to Highlight DA Interactions

The packing interactions of a series of electron donor (D) and electron acceptor (A) charge transfer (CT) near-IR absorbers based on platinum-dithiolene complexes are reinvestigated here as a case study also by using the Hirshfeld surface analysis. This analysis on systems, which exhibit the 1:1, 2:1 and 2:2 columnar stacking patterns between D and A, allows us to point out that several interactions of atoms and fragments are involved in the stacking interactions but also that only a limited fraction of these interactions, limited to the 1:1 D/A columnar stacking case, can be relatable to the absorption features of this class of compounds.

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.

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.

A radical mixed-ligand gold bis(dithiolene) complex

Asymmetry in the electronic structure of a mixed-ligand gold bis(dithiolene) complex explains its peculiar optical, electrochemical and structural features.

Near-infrared dyes for two-photon absorption in the short-wavelength infrared: strategies towards optical power limiting

The recent advances in the field of two-photon absorbing chromophores in the short-wavelength infrared spectral range (SWIR 1100–2500 nm) are summarized, highlighting the development of optical power limiting devices in this spectral range.

Nickel(II) complexes based on dithiolate-polyamine binary ligand systems: crystal structures, hirshfeld surface analysis, theoretical study, and catalytic activity study on photocatalytic hydrogen generation

To ascertain the influence of binary ligand systems [1,1-dicyanoethylene-2,2-dithiolate (i-mnt-2) and polyamine {tetraen = tris(2-aminoethyl)amine, tren = diethylene triamine and opda = o-phenylenediamine}] on the coordination modes of the Ni(ii) metal center and resulting supramolecular architectures, a series of nickel(ii) thiolate complexes [Ni(tetraen)(i-mnt)](DMSO) (1), [Ni2(tren)2(i-mnt)2] (2), and [Ni2(i-mnt)2(opda)2]n (3) have been synthesized in high yield in one step in water and structurally characterized by single crystal X-ray crystallography and spectroscopic techniques. X-ray diffraction studies disclose the diverse i-mnt-2 coordination to the Ni+2 center in the presence of active polyamine ligands, forming a slightly distorted octahedral geometry (NiN4S2) in 1, square planar (NiS4) and distorted octahedral geometries (NiN6) in the bimetallic co-crystallized aggregate of cationic [Ni(tren)2]+2 and anionic [Ni(i-mnt)2]-2 in 2, and a one dimensional (1D) polymeric chain along the [100] axis in 3, having consecutive square planar (NiS4) and octahedral (NiN6) coordination kernels. The N-HO, N-HS, N-HN, N-HS, N-HN, and N-HO type hydrogen bonds stabilize the supramolecular assemblies in 1, 2, and 3 respectively imparting interesting graph-set-motifs. The molecular Hirshfeld surface analyses (HS) and 2D fingerprint plots were utilized for decoding all types of non-covalent contacts in the crystal networks. Atomic HS analysis of the Ni+2 centers reveals significant Ni-N metal-ligand interactions compared to Ni-S interactions. We have also studied the unorthodox interactions observed in the solid state structures of 1-3 by QTAIM and NBO analyses. Moreover, all the complexes proved to be highly active water reduction co-catalysts (WRC) in a photo-catalytic hydrogen evolution process involving iridium photosensitizers, wherein 2 and 3 having a square planar arrangement around the nickel center(s) - were found to be the most active ones, achieving 1000 and 1119 turnover numbers (TON), respectively.

Dithiol-Dithione Tautomerism of 2,3-Pyrazinedithiol in the Synthesis of Copper and Silver Coordination Compounds

A promising strategy for new electrically conductive coordination polymers is the combination of d¹⁰ metal ions, which tolerate short metal···metal distances, with dithiolene linkers, known for their "non-innocent" redox behavior. This study explores the coordination chemistry of 2,3-pyrazinedithiol (H₂pdt) toward Cu⁺ and Ag⁺ ions, highlighting similarities and differences. The synthetic approach, starting with the fully protonated ligand, allowed the isolation of a homoleptic bis(dithiolene) complex with formal Cu^I atoms, [Cu(H₂pdt)₂]Cl (1). This complex was further transformed to a 1D coordination polymer with short metal···metal distances, ^1D[Cu(Hpdt)] (2^Cu). The larger Ag⁺ ion directly built up a very similar coordination polymer, ^1D[Ag(Hpdt)] (2^Ag), without any appearance of an intermediate metal complex. The coordination polymer ^1D[Cu(H₂pdt)I] (4), like complex 1, bears fully protonated H₂pdt ligands in their dithione form. Upon heating, both compounds underwent auto-oxidation coupled with a dehydrogenation of the ligand to form the open-shell neutral copper(II) complex [Cu(Hpdt)₂] (3) and the coordination polymer ^1D[Cu₂I₂(H₂pdt)(Hpdt)] (5), respectively. For all presented compounds, crystal structures are discussed in-depth. Furthermore, properties of 1, 3, and those of the three 1D coordination polymers, 2^Ag, 2^Cu, and 4, were investigated by UV-vis-NIR spectroscopy, cyclic voltammetry, and variable-temperature magnetic susceptibility, and direct current (dc)-conductivity measurements. The experimental results are compared and discussed with the aid of DFT simulations.

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.

Dithione, the antipodal redox partner of ene-1,2-dithiol ligands and their metal complexes

Defining the oxidation state of the central atom in a coordination compound is fundamental in understanding the electronic structure and provides a starting point for elucidating molecular properties. The presence of non-innocent ligand(s) can obscure the oxidation state of the central atom as the ligand contribution to the electronic structure is difficult to ascertain. Redox-active ligands, such as dithiolene ligands, are well known non-innocent ligands that can exist in both a fully reduced (Dt2-) and fully oxidized (Dt0) states. Complexes containing the fully oxidized dithione state of the ligand are uncommon and only a few have been completely characterized. Dithione ligands are of interest due to their electron-deficient nature and ability to act as an electron acceptor for more electron-rich moieties, such as other dithiolene ligands or metal centers. This article focuses the syntheses, structures, and metal coordination, particularly coordination compounds, of dithione ligands. Various examples of mono, bis, and tris dithione complexes are discussed.

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.

Metal-Dithiolene Bonding Contributions to Pyranopterin Molybdenum Enzyme Reactivity

Here we highlight past work on metal-dithiolene interactions and how the unique electronic structure of the metal-dithiolene unit contributes to both the oxidative and reductive half reactions in pyranopterin molybdenum and tungsten enzymes. The metallodithiolene electronic structures detailed here were interrogated using multiple ground and excited state spectroscopic probes on the enzymes and their small molecule analogs. The spectroscopic results have been interpreted in the context of bonding and spectroscopic calculations, and the pseudo-Jahn-Teller effect. The dithiolene is a unique ligand with respect to its redox active nature, electronic synergy with the pyranopterin component of the molybdenum cofactor, and the ability to undergo chelate ring distortions that control covalency, reduction potential, and reactivity in pyranopterin molybdenum and tungsten enzymes.

Recent advances in the mechanisms of the hydrogen evolution reaction by non-innocent sulfur-coordinating metal complexes

This review comments on the homogeneous HER mechanisms for catalysts carrying S-non-innocent ligands in the light of experimental and computational data.

Functional group induced structural diversities and photocatalytic, magnetic and luminescence sensing properties of four cobalt(ii) coordination polymers based on 1,3,5-tris(2-methylimidazol-1-yl)benzene

Based on the designed tripodal linker timb, four cobalt(ii) coordination polymers, {[Co₄(timb)₂(Br–IPA)₄]·5H₂O}_n (1), {[Co(timb)_0.5(NH₂–IPA)]·4H₂O}_n (2), {[Co₅(timb)₄(OH–IPA)₄]·2NO₃·2DMA·2H₂O}_n (3), and {[Co₃(timb)₂(SO₃–IPA)₂(H₂O)₂]·8H₂O}_n (4), have been obtained.

Heterometallic coordination polymers based on homo- and heteroleptic Au(iii) dithiolene complexes

Two novel hetero- and homoleptic Au(iii) dithiolene complexes have been designed, synthesized, characterized and employed for the elaboration of heterometallic coordination networks.

Potential modulations in flatland: near-infrared sensitization of MoS2 phototransistors by a solvatochromic dye directly tethered to sulfur vacancies

Near-infrared sensitization of monolayer MoS₂ is here achieved via the covalent attachment of a novel heteroleptic nickel bis-dithiolene complex into sulfur vacancies in the MoS₂ structure. Photocurrent action spectroscopy of the sensitized films reveals a discreet contribution from the sensitizer dye centred around 1300 nm (0.95 eV), well below the bandgap of MoS₂ (2.1 eV), corresponding to the excitation of the monoanionic dithiolene complex. A mechanism of conductivity enhancement is proposed based on a photo-induced flattening of the corrugated energy landscape present at sulfur vacancy defect sites within the MoS₂ due to a dipole change within the dye molecule upon photoexcitation. This method of sensitization might be readily extended to other functional molecules that can impart a change to the dielectric environment at the MoS₂ surface under stimulation, thereby extending the breadth of detector applications for MoS₂ and other transition metal dichalcogenides.

The coordination behavior of 2,3-bis(diphenylphosphino)maleic-N-phenylimide towards copper, silver, gold and palladium

In the coordination sphere of copper, silver and palladium 2,3-bis(diphenylphosphino)maleic-N-phenylimide can act as a radical, non-innocent ligand.

A comparative theoretical study on the optoelectronic and nonlinear optical properties of [Pt(bpy)(qdt)] derivatives with electron-donating and -withdrawing anchors

A series of [Pt(bpy)(qdt)] {bpy = 2,2′-bipyridine; qdt = quinoxaline-2,3-dithiolate} derivatives was chosen to study the effect of structural modifications on the optoelectronic and nonlinear optical (NLO) properties of the molecules.

Stabilization of different redox levels of a tridentate benzoxazole amidophenoxide ligand when bound to Co(iii) or V(v)

The electronic structure of Co and V complexes of a tridentate benzoxazole-containing aminophenol ligand NNOH2 were characterized by both experimental and theoretical methods.

Broadband near-IR absorbing Au-dithiolene complexes bearing redox-active oligothiophene ligands

A series of three homoleptic, monoanionic gold dithiolene complexes of oligothiophene ligands which coordinate via a central thiophene-3,4-dithiolate chelate are presented. The oligomer chains are three, five and seven thiophenes long and the complexes display hybrid optoelectronic properties featuring characteristics of both the oligothiophene chains and the delocalised metal dithiolene centre. The properties of the complexes have been characterised using a variety of spectroscopic and electrochemical methods complemented by computational studies. Solid state spectroelectrochemistry has revealed that upon oxidation these complexes display intense and broad absorption across the visible spectrum. In attempting to produce nickel analogues of these materials a single crystal of a photo-oxidised nickel dithiolene complex has also been isolated.

A Series of Compounds Based on [P2W18O62]6- and Transition Metal Mixed Organic Ligand Complexes with High Catalytic Properties for Styrene Epoxidation

Seven compounds based on [P₂W₁₈O₆₂]^6- ({P₂W₁₈}) were successfully prepared and carefully characterized. [HC₅H₅N][Cu(2,2'-bpy)₂]₂[HP₂W₁₈O₆₂]·2H₂O (bpy = bipyridine) (1) is constructed from {P₂W₁₈} bridged by [Cu(2,2'-bpy)₂]²⁺. [HC₅H₅N][Zn(2,2'-bpy)₂]₂[HP₂W₁₈O₆₂]·4H₂O (1a) is isostructural and isomorphous with compound 1. [Cu₄(2,2'-bpy)₃(nic)₃(OH)₂(H₂O)][H₃P₂W₁₈O₆₂]·0.5H₂O (nic = nicotinic acid) (2) is formed by {P₂W₁₈} and tetracopper transition metal mixed organic ligand complexes (TMMCs). [Cu₂(2,2'-bpy)₂(C₂O₄)]₃[P₂W₁₈O₆₂]·3H₂O (3) is made up of {P₂W₁₈} and bicopper TMMCs, [Cu₆(2,2'-bpy)₆(OH)₆][P₂W₁₈O₆₂]·2H₂O (4) is built up from {P₂W₁₈}, and hexacopper complexes of 2,2'-bpy and hydroxyls. [Cu(2,2'-bpy)(hnic)_0.5][Cu₃(2,2'-bpy)₃(hnic)₂(H₂O)₂][H₃P₂W₁₈O₆₂] (hnic = hydroxyl nicotinic acid) (5a) contains two different TMMCs. In addition, compound 5a is the first example of a compound that contains Cu-π interactions. [Cu₂(2,2'-bpy)₂(hnic)][H₄P₂W₁₈O₆₂]· xH₂O ( x ≈ 50) (5b) is based on {P₂W₁₈} and [Cu₂(2,2'-bpy)₂(hnic)]²⁺. We discuss the mechanisms for the formations of these compounds. All the catalytic performances of the compounds for styrene epoxidation to styrene oxide are high.

Tuning of Thiyl/Thiolate Complex Near-Infrared Chromophores of Platinum through Geometrical Constraints

The chemistry of radical-ligand complexes of the transition metals has developed into a vibrant field of research that spans from fundamental studies on the relationship between the chemical and electronic structures to applications in catalysis and functional materials chemistry. In general, fine-tuning of the relevant properties relies on an increasingly diversifying pool of radical-proligand structures. Surprisingly, the variability of the conformational freedom and the number of distinct bonding modes supported by many radical proligands is limited. This work reports on the angular constraints and relative geometric alignment of metal and ligand orbitals as key parameters that render a series of chemically similar thiyl/thiolate complexes of platinum(II) electronically and spectroscopically distinct. The use of conformational flexible thiophenols as primary ligand scaffolds is essential to establishing a defined radical-ligand [(^areneS)₂Pt^II]^•+ core whose electronic structure is modulated by a series of auxiliary coligands at platinum.

Uncommon Optical Properties and Silver-Responsive Turn-Off/On Luminescence in a PtII Heteroleptic Dithiolene Complex

Complex [Pt(iPr₂ pipdt)(Quinoxdt)] (iPr₂ pipdt=1,4-diisopropyl-piperazine-2,3-dithione; Quinoxdt=[1,4]dithiino[2,3-b]quinoxaline-2,3-dithiolate) exhibits a remarkable green emission at 570 nm (room temperature), which is above the lowest excited state. The complex is characterized by negative solvatochromism as well as a high second-order polarizability. Addition of Ag^I ions induces 1) hypsochromic shift of the lowest frequencies and 2) reversible quenching of luminescence. The corresponding Ni and Pd complexes have also been prepared and investigated to assist interpretation of optical properties within the triad. Computational studies based on DFT and time-dependent DFT highlight the electronic properties of [Pt(iPr₂ pipdt)(Quinoxdt)]. The preferential site of interaction between the Pt complex and incoming Ag^I is evidenced by the shape of the Fukui functions, pointing to the thiolic sulfur and platinum atoms as the most reactive sites towards a soft cation. Calculated optical properties are in agreement with experimental findings. This study sheds light on the structure-property relationship for this class of compounds.

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.

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.

Coordination Programming of Two-Dimensional Metal Complex Frameworks

Since the discovery of graphene, two-dimensional materials with atomic thickness have attracted much attention because of their characteristic physical and chemical properties. Recently, coordination nanosheets (CONASHs) came into the world as new series of two-dimensional frameworks, which can show various functions based on metal complexes formed by numerous combinations of metal ions and ligands. This Feature Article provides an overview of recent progress in synthesizing CONASHs and in elucidating their intriguing electrical, sensing, and catalytic properties. We also review recent theoretical studies on the prediction of the unique electronic structures, magnetism, and catalytic ability of materials based on CONASHs. Future prospects for applying CONASHs to novel applications are also discussed.

Near-IR absorbing donor-acceptor ligand-to-ligand charge-transfer complexes of nickel(ii)

A new series of square-planar nickel(ii) donor-acceptor complexes exhibiting ligand-to-ligand charge-transfer (LL'CT) transitions have been prepared. Whereas the use of a catecholate donor ligand in conjunction with a bipyridyl acceptor ligand affords a complex that absorbs throughout the visible region, the use of a azanidophenolate donor ligands in conjunction with a bipyridyl acceptor ligand affords complexes that absorbs well into the near-IR region of the solar spectrum. Three new complexes, (cat)Ni(bpy t Bu2) (1; (cat)2- = 3,5-di-tert-butyl-1,2-catecholate; bpy t Bu2 = 4,4'-di-tert-butyl-2,2'-bipyridine), (ap)Ni(bpy t Bu2) (2; (ap)2- = 4,6-di-tert-butyl-2-(2,6-diisopropylphenylazanido)phenolate), and (apPh)Ni(bpy t Bu2) (3; (apPh)2- = 10-(2,6-diisopropylphenylazanido)-9-phenanthrolate), have been prepared and characterized by structural, electrochemical, and spectroscopic methods. Whereas all three square-planar complexes show multiple reversible one-electron redox-processes and strong LL'CT absorption bands, in azanidophenolate complexes 2 and 3, the LL'CT absorption covers the near-IR region from 700-1200 nm. The electronic absorption spectra and ground state electrochemical data for 2 and 3 provide an estimate of their excited-state reduction potentials, E+/*, of -1.3 V vs. SCE, making them as potent as the singlet excited state of [Ru(bpy)3]2+.

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.

Structural tailoring of the NIR-absorption of bis(1,2-dichalcogenolene) Ni/Pt electrochromophores deriving from 1,3-dimethyl-2-chalcogenoxo-imidazoline-4,5-dichalcogenolates

Bis(1,2-dithiolene) and (1,2-diselenolene) Ni and Pt complexes with 2-chalcogenoxo-imidazoline-4,5-dichalcogenolates show intense NIR electrochromism tunable by structural modifications.

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.

A nonlinear optical active polymer film based on Pd(ii) dithione/dithiolate second-order NLO chromophores

A film of [Pd(Dod₂pipdt)(dmit)] incorporated into a polymethylmethacrylate matrix, showing a good second-harmonic generation, has been prepared for the first time in the class of dithione–dithiolate 2^ndorder NLO-chromophores.

Large Ligand Folding Distortion in an Oxomolybdenum Donor-Acceptor Complex

Interligand charge transfer is examined in the novel metallo-dithiolene complex MoO(SPh)2((i)Pr2Dt(0)) (where (i)Pr2Dt(0) = N,N'-isopropyl-piperazine-2,3-dithione). The title complex displays a remarkable 70° "envelope"-type fold of the five-membered dithiolene ring, which is bent upward toward the terminal oxo ligand. A combination of electronic absorption and resonance Raman spectroscopies have been used to probe the basic electronic structure responsible for the large fold-angle distortion. The intense charge transfer transition observed at ∼18 000 cm(-1) is assigned as a thiolate → dithione ligand-to-ligand charge transfer (LL'CT) transition that also possesses Mo(IV) → dithione charge transfer character. Strong orbital mixing between occupied and virtual orbitals with Mo(x(2)-y(2)) orbital character is derived from a strong pseudo Jahn-Teller effect, which drives the large fold-angle distortion to yield a double-well potential in the electronic ground state.