Nickel Dithiolene Research Articles

Exhaustive oxidation of a nickel dithiolate complex: some mechanistic insights en route to sulfate formation

A study of the step-wise oxidation of a Ni(II) diaminodithiolate complex through the formation of sulfate, the ultimate sulfur oxygenate, is reported. Controlled oxygenations or peroxidations of a neutral, planar, tetracoordinate, low-spin Ni(II) complex of a N(2)S(2)-donor ligand, (N,N'-dimethyl-N-N'-bis(2-mecaptoethyl)-1,3-propanediaminato) nickel(ii) (1), led to a series of sulfur oxygenates that have been isolated and characterized by ESI-MS and single-crystal X-ray diffraction. A monosulfenate complex (2) was detected by ESI-MS as a product of oxidation with one equivalent of H(2)O(2). However, this complex proved too unstable to isolate. Reaction of the dithiolate (1) with two equivalents of H(2)O(2) or one O(2) molecule leads to the formation of a monosulfinate complex (3), which was isolated and fully characterized by crystallography. The oxidation product of the monosulfinate (3) produced with either O(2) or H(2)O(2) is an interesting dimeric complex containing both sulfonate and thiolate ligands (4), this complex was fully characterized by crystallography, details of which were reported earlier by us. A disulfonate complex (7) is produced by reaction of 1 in the presence of O(2) or by reaction with exactly six equivalents of H(2)O(2). This complex was isolated and also fully characterized by crystallography. Possible intermediates in the conversion of the monosulfinate complex (3) to the disulfonate complex (7) include complexes with mixed sulfonate/sulfenate (5) or sulfonate/sulfinate (6) ligands. Complex 5, a four-oxygen adduct of 1, was not detected, but the sulfonate/sulfinate complex (6) was isolated and characterized. The oxidation chemistry of 1 is very different from that reported for other planar cis-N(2)S(2) Ni(ii) complexes including N,N'-dimethyl-N-N'-bis(2-mecaptoethyl)-1,3-ethylenediaminato) nickel(II), (8), and N,N'-bis(mercaptoethyl)-1,5-diazacyclooctane nickel(II). To address the structural aspects of the reactivity differences, the crystal structure of 8 was also determined. A comparison of the structures of planar Ni(II) complexes containing cis-dithiolate ligands, strongly suggests that the differences in reactivity are determined in part by the degree of flexibility that is allowed by the NN' chelate ring.

Theoretical Studies on the Ethylene Purification Using Substituted Nickel Dithiolenes

The world is running out of energy, thus energy preservation is of paramount importance. Using current technology, ethylene is purified from petroleum feed stocks using the very energy intensive cryogenic distillation method. However, a purification procedure based on the redox properties of nickel bis-dithiolene complexes has been theoretically studied, in order to design a more convenient route to ethylene purification. Several possible addition routes of ethylene to neutral and anionic Ni(S2C2(CN)2)2 complexes have been modeled using density functional theory. An intraligand addition and subsequent decomposition is preferred for the neutral complex, while the interligand adduct is formed in the presence of the anion, in line with previous experimental results. The effect of the anion, whose role is as a mediator in the initial step of the reaction, is discussed, and the ability of this compound to avoid poisoning by acetylene is investigated. The results from the CN substituted complex are then compared with that of ethylene addition to CF3, H, and OH substituted nickel dithiolene complexes.

Density functional theory study on the mechanism and thermochemistry of olefins addition to nickel dithiolenes

We investigated the reaction mechanism and thermochemical property of conjugated dienes or mono-olefins with nickel dithiolenes (Ni(S2C2R2)2) using density functional theory. The reactions between conjugated dienes and nickel dithiolenes are concerted reactions. The thermochemical property study shows that the introduction of electron-withdrawing groups (–CF3 or –CN) to nickel dithiolene (Ni(S2C2H2)2) not only significantly lowers the activation energy barrier but also strongly stabilises the products. The introduction of electron-donating group (–CH3) to butadiene has the same effect. So, we conclude that the reactions between nickel dithiolenes and conjugated dienes are electrophilic cycloaddition. Mono-olefins can add to nickel dithiolenes through interligand pathway, which is a two-step process or through intraligand pathway, which is a one-step process. The thermochemical property study shows that the activation enthalpy for the reaction of butadiene with Ni(S2C2(CF3)2)2 is much lower than those of C4 mono-olefins with Ni(S2C2(CF3)2)2 for both interligand addition and intraligand addition. The Gibbs free energy for the reaction of butadiene with Ni(S2C2(CF3)2)2 is also more favourable than those of C4 mono-olefins with Ni(S2C2(CF3)2)2. It is the very preferential pathway for Ni(S2C2(CF3)2)2 to bind butadiene than C4 mono-olefins.

Theoretically Study on the Reaction Complexing Olefins with Nickel Dithiolene

Theoretically Study on the Reaction Complexing Olefins with Nickel Dithiolene

Nanocomposites of carbon quantum dots–nickel(ii) dithiolene as nanolights

Three types of nanocrystals (viz., nanodiscs, rectangular prisms and hexagonal prisms) of the nickel(II) dithiolene complex, [PPh4][NiII(L2−)(L1−●)], 1 [L = 1,2-dicarbomethoxyethylene dithiolate] displaying solvent dependent shapes and characteristic SAED patterns are reported. On doping with CQDs these non-luminescent nanocrystals form nanocomposites which show a wide range of photoluminescence depending on the size of the CQD used, and the various nanocrystalline shapes of complex 1 can be optically imaged by CQD treatment that is reminiscent of cellular bioimaging.

Indole-substituted nickel dithiolene complexes in electronic and optoelectronic devices

The synthesis and full characterisation of a novel indole-substituted nickel dithiolene [Ni(mi-5edt)2] (3) is reported, and compared to its alkyl-substituted analogue [Ni(mi-5hdt)2] (4) that has been previously communicated [Dalgleish et al., Chem. Commun., 2009, 5826] [mi-5edt = 1-(N-methylindol-5-yl)-ethene-1,2-dithiolate; mi-5hdt = 1-(N-methylindol-5-yl)-hex-1-ene-1,2-dithiolate)]. Both complexes are shown to undergo oxidative electropolymerisation, yielding polymer films that retain the redox and optical properties of the monomer. The more soluble analogue 4 is shown to form high quality thin films by spin coating, which have been utilised to fabricate field-effect transistors (FETs) and bulk heterojunction photovoltaic devices (BHJ-PVs). From FET studies, the material shows ambipolar charge transport behaviour, with a maximum carrier mobility of ∼10−6 cm2 V−1s−1 for electrons. By using 4 simultaneously as the electron acceptor as well as a NIR sensitiser in BHJ-PVs, the complex is shown to contribute to the photocurrent, extending light harvesting into the NIR region.

Electrodeposition as a superior route to a thin film molecular semiconductor

Electrooxidation to form neutral films of a homoleptic nickel dithiolene [Ni(b-3ted)2] (1) from an air-stable TBA salt is described [b-3ted = bis(3-thienyl)-1,2-ethylenedithiolene; TBA = tetrabutylammonium]. Films grown by potentiostatic electrodeposition directly onto interdigitated electrode arrays show improved conductivity compared to those formed by solution methods. The grown films are free from residual electrolyte doping, and this technique is shown to yield robust films of reproducible electronic performance. The conductivity of films formed by electrodeposition show gate dependence when grown directly onto field effect transistor substrates. Thin-film X-ray diffraction confirms the electrodeposited films to be of the same polymorph as films and single crystals formed by solution methods. Scanning electron microscopy shows the electrodeposited films to have larger, more connected polycrystalline regions, as well as improved contact with the electrodes.

A Nickel(II)–Sulfur‐Based Radical‐Ligand Complex as a Functional Model of Hydrogenase

Better than nature! A nickel(II) dithiolene complex [NiII(L2−)(L−.)][PPh4] (1; see figure; L=1,2-dicarbomethoxyethylene dithiolate) electrocatalyzes hydrogen evolution at the lowest achievable reduction potential (, −0.69 V) in CH3CN and also in aqueous medium (, −0.71 V) to date. Compound 1 shows strikingly similar EPR and reduction potential values to those observed with native Ni-containing hydrogenases.

Transient nonlinear optical response of some symmetrical nickel dithiolene complexes

The transient nonlinear optical response of some recently synthesized symmetric nickel dithiolene complexes, namely the Ni(etodddt) 2 (etodddt = 4,5-(1,4-oxathiane-2,3-diyldithio)-1,3-dithiole), the Ni(pddt) 2 (i.e., bis(6,7-dihydro-5H-[1,4]dithiepine-2,3-ddithiole) nickel)) and the Ni(dddt) 2 (bis(5,6-dihydro-1,4-dithiine-2,3-dithiole) nickel), is studied using Z-scan technique employing 1064 and 532 nm, nanosecond laser pulses. The absorptive and the refractive parts of the third-order susceptibility χ (3) were determined and the second hyperpolarizability γ of each dithiolene complex was deduced at both excitation wavelengths, while strong resonance enhancement was found to occur under 1064 nm excitation. The present results are discussed and compared with other literature results obtained on similar symmetric and unsymmetric dithiolene complexes.

Synthesis, characterization, spectroscopy, electronic and redox properties of a new nickel dithiolene system

A new dithiolene ligand with 3,5-dibromo substituted phenyl groups was designed and synthesized. The protected form of the ligand was reacted with a nickel salt providing neutral Ni(S 2C 2(3,5-C 6H 3Br 2) 2) 2 and anionic [Ni(S 2C 2(3,5-C 6H 3Br 2) 2) 2] − isolated as a Bu 4N + salt. Both were characterized by UV–Vis and IR spectroscopy and compared with the similar known molecular systems. They exhibit intense low energy transitions that are characteristic of such systems. The electrochemical behavior of these molecules was investigated by cyclic voltammetry.

Synthesis and characterization of a new π-extended nickel dithiolene complex for molecular materials

A new nickel complex consisting of extended thiophenedithiolene ligands has been synthesized. The complex has been characterized by UV–vis–NIR spectroscopy, mass spectrometry, cyclic voltammetry, and X-ray crystallography. The complex exhibits significant electron delocalization into the peripheral thiophene rings. The −1 complex displays diamagnetic behavior in the solid state, but is paramagnetic ( S = 1/2) in solution. X-ray analysis shows a number of close contacts which could explain the diamagnetism.

Cleavage of Ni-(μ2-S)-Ni Bridges in Dinuclear Nickel(II) Dithiolate Pincer Complexes and Related Reactions

Pyridine-2,6-dimethanethiolate and pyridine-2,6-dithiocarboxylate form sparingly soluble Ni(II) pincer complexes formulated as [Ni(pdmt)](2) and [Ni(pdtc)](2), respectively, with two Ni-(mu(2)-S)-Ni bridges. In acetonitrile reaction systems, the latter undergoes the facile bridge cleavage reactions [Ni(pdtc)](2) + 2L(0,-) --> 2[Ni(pdtc)L](0,-) with an extensive set of nucleophiles to afford planar mononuclear products with L(-) = halide, CN, Me(3)SiO(-), RS(-) and L(0) = Et(3)P and a N-heterocyclic carbene. [Ni(pdmt)](2) is considerably less reactive toward bridge disruption. Cleavage products support several reactions of interest leading to other mononuclear species and to di- and trinuclear complexes. [Ni(pdtc)(OSiMe(3))](1-) deprotonates acetonitrile and acetone to form [Ni(pdtc)(CH(2)R)](1-) (R = CN, COMe). Reaction of [Ni(pdtc)SEt](1-) with Fe(II) yields the thiolate-bridged dimer {[Ni(pdtc)](2)(SEt)}(1-). Refluxing an acetonitrile solution of [Ni(pdtc)SH](1-) in air results in formation of trinuclear [Ni(pdtc)](3)S](2-) containing the rare unsupported Ni(3)(mu(3)-S) bridge core. Reaction of [Ni(pdtc)CN](1-) with [Fe(Me(6)tren)(OTf)](1+) forms the complex [Ni(pdtc)CNFe(Me(6)tren)](1+), the only example of a single Ni-C[triple bond]N-Fe bridge within a molecule. Structures of the various types of reaction products are presented. This work demonstrates the potential utility of bridge cleavage of polynuclear Ni(II) thiolates, an extensive family of compounds, to produce mononuclear products.

Bimolecular recombination in ambipolar organic field effect transistors

In ambipolar organic field effect transistors (OFET) the shape of the channel potential is intimately related to the recombination zone width W, and hence to the electron–hole recombination strength. Experimentally, the recombination profile can be assessed by scanning Kelvin probe microscopy (SKPM). However, surface potentials as measured by SKPM are distorted due to spurious capacitive couplings. Here, we present a (de)convolution method with an experimentally calibrated transfer function to reconstruct the actual surface potential from a measured SKPM response and vice versa. Using this scheme, we find W = 0.5 μm for a nickel dithiolene OFET, which translates into a recombination rate that is two orders of magnitude below the value expected for Langevin recombination.

Bis[(E)-1-(3,4-dichlorobenzylideneamino)-4-methylpyridinium] bis(maleonitriledithiolato)nickelate(II)

The asymmetric unit of the title compound, (C13H11Cl2N2)2[Ni(C4N2S2)2], contains one-half of a centrosymmetric [Ni(mnt)2] anion (where mnt is maleonitrile­dithiol­ate or 1,2-dicyano-1,2-ethyl­enedithiol­ate) and an (E)-1-(3,4-dichloro­benzyl­ideneamino)-4-methyl­pyridinium cation. In the anion, the coordination around the Ni atom is a distorted square. In the cation, the aromatic rings are oriented at a dihedral angle of 7.81 (3)°. In the crystal structure, inter­molecular C—H⋯N hydrogen bonds link the cations and anions. π–π Contacts between the nickel dithiol­ene and pyridine rings and between the benzene and pyridine rings, [centroid–centroid distances = 3.682 (3) and 3.643 (3) Å, respectively] may further stabilize the structure.

Square-planar mixed ligand nickel dithiolenes as second-order non-linear chromophores: synthesis and characterisation of [Ni(Me2pipdt)(dddt)

AbstractThe novel [Ni(Me 2 pipdt)(dddt)] complex based on the Me 2 pipdt (1,4-dimethylpiperazine-3,2-dithione) and dddt (5,6-dihydro-1,4-dithine-2,3-dithiolate) ligands has been synthesised and characterised. Structural data, vibrational marker, solvatochromic behaviour of the typical absorption in the near infrared region, and approximate theoretical calculations suggest that an unbalanced electron distribution at the dithiolene core occurs in the ground and excited states. In particular, the dddt ligand gives a prevailing contribution to the HOMO, and Me 2 pipdt to the LUMO. The charge-transfer character of the HOMO-LUMO transition makes this complex a potential second-order non-linear optic chromophore.Graphical Abstract[IMAGE]

Synthesis, structure and spectroscopic properties of a new class of polymerisable nickel dithiolenes

The synthesis, structure and spectroscopic properties of a new class of asymmetric nickel dithiolene complex containing pendent thiophene units [Ni(R2pipdt)(b-3ted)] are described {R = Bz (3), iPr (4); pipdt = piperazine-3,2-dithione; b-3ted = bis(3-thienyl)-1,2-ethylenedithiolene}. X-ray crystallography of both neutral species shows planar nickel dithiolene units and the thiophene groups twisted out of the molecular plane, with the R group having a large effect on the packing structure. DFT geometry calculations show good agreement with experimental data for 3 and 4 and confirm that the low energy absorption, assigned to a HOMO → LUMO transition, is inter-ligand charge-transfer in character. Solid state calculations show greater band dispersion in 4, which corresponds to a closer packing in the crystal lattice. Cyclic voltammetry of both complexes displays three reversible processes, corresponding to an interconversion between cationic, neutral, anionic and dianionic species, with tuning of the redox potentials by variation of the R group. Electrochemical polymerisation of 3 shows incorporation of intact dithiolene units into a polymer film with redox functionality similar to that of the monomer, whereas co-polymerisation of 3 with thiophene yields a highly conductive film with redox functionality similar to polythiophene and enhanced absorption across the near IR.

A stable near IR switchable electrochromic polymer based on an indole-substituted nickel dithiolene

A novel nickel dithiolene-containing polymer, generated by the electropolymerisation of pendent indole units, has been prepared and shows good stability and fast reversible switching of the near infrared absorption by varying the applied potential of the film.

Electronic structure and X-ray spectra of nickel(II) dithiolate chelate complexes

Nickel(II) dithiocarbamate and dithiophosphinate complexes were studied by X-ray and X-ray photoelectron spectroscopy. The X-ray emission and absorption spectra of Ni(II) compounds were interpreted in terms of quantum-chemical model calculations of the electronic spectrum of the complexes. The electronic structure of nickel(II) dithiolates was analyzed on the basis of the experimental and theoretical data.

Nickel Dithiolene Chelate Rings in a New Role as η5-Coordinating Ligands: Synthesis, Structural Characterization, and Redox Reactivity of an “Fe2Ni” Bis-Double-Decker

A bis-double-decker complex has been assembled from the nickel bisdithiolene complex [Ni(S 2C 2Me 2) 2] (1-/2-) and two [Cp*Fe] (+) units (Cp* = C 5Me 5). The complex, [(eta (5)-Cp*-Fe-mu-eta (5),eta (5)-((S 2C 2Me 2) 2Ni)Fe-eta (5)-Cp*] ( n ) ( 1 ( n )), was isolated in two charge states ( n = 0, 1). The structure of 1 (+) was confirmed by X-ray crystallography for 1 (+)PF 6 (-) and 1 (+)BF 4 (-), and it shows the nickel bisdithiolene units pi-donating to iron centers. Both salts crystallize in a centrosymmetric space group (center of inversion at nickel). Computational (density functional theory) data indicate a highly delocalized spin density for 1 (+). The reaction of 1 with 1 or 2 equiv of HBF 4 leads to oxidation to form 1 (+) or 1 (2+), respectively. On an electrochemical time scale, reversibility is observed for the redox series 1/ 1 (+)/ 1 (2+), with an additional slower step for oxidation of 1 (2+).

Continuous Production of a Near Infrared Absorbing Chromophore

The nickel dithiolene complex-type near-infrared chromophore, nickel bis-(1,2-diisopropylthioethane-1,2-dithiolene), was synthesized in three reaction steps and applied to a near-infrared cutoff filter for PDP TV. A microreactor was employed in the strong exothermic reaction of 2-propanethiol and oxalyl chloride. A 90% yield of S,S′-diisopropyl dithiooxalate was obtained with a 75% reduction in solvent usage. Thionation of S,S′-diisopropyl dithiooxalate with the use of tetraphosphorus decasulfide and aluminum hydroxide provided a clean dithiolene feed for the next continuous step. The final product was efficiently produced in a microreactor and a tubular reactor in series using nickel chloride solution and dithiolene synthesized from thionation in a batch reactor.