Gold Dithiolene Complexes Research Articles

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 (σRT = 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.

High Ambipolar Mobility in a Neutral Radical Gold Dithiolene Complex

AbstractA new anionic gold dithiolene complex NBu4·[1] is synthesized from the (1‐((1,1‐biphenyl)‐4‐yl‐)‐ethylene‐1,2‐dithiolene ligand 1, and the cis and trans isomers are separated by recrystallization. The trans isomer is oxidized via electrocrystallisation to the neutral gold dithiolene complex 2. Complex 2 crystalizes in 1D chains, held together by short (3.30–3.37 Å) S–S contacts, which are packed in a herringbone arrangement in the ab‐plane. The complex exhibits semiconductor behavior (σRT = 1.5 × 10−4 S cm−1) at room temperature with a small activation energy (Ea = 0.11 eV), with greater conductivity along the stacking direction. The charge transport behavior of complex 2 is further investigated in single‐crystal field‐effect transistor (FET) measurements, the first such measurements reported for gold dithiolene complexes. Complex 2 shows incredibly balanced ambipolar behavior in the single‐crystal field‐effect transistor (SC‐FET), with high charge‐carrier mobilities of 0.078 cm2 V−1 s−1, the highest ambipolar mobilities reported for metal dithiolene complexes. This well‐balanced behavior, along with the activated conductivity and band structure calculations, suggests that 2 behaves as a Mott insulator. The magnetic properties are also studied by superconducting quantum interference device (SQUID) magnetometry and solid state 1H NMR, with evidence of a nonmagnetic ground state at low temperature.

Subtle Steric Differences Impact the Structural and Conducting Properties of Radical Gold Bis(dithiolene) Complexes.

Among single component molecular conductors, neutral radical gold dithiolene complexes [(R-thiazdt)2 Au]. derived from the N-alkyl-1,3-thiazoline-2-thione-4,5-dithiolate (R-thiazdt) ligand provide an extensive series of conducting, non-dimerized, half-filled band systems. Analogues of the known R=isopropyl (iPr) derivative were investigated here with R=NMe2 , cyclopropyl (cPr) and n-propyl (nPr), aiming at rationalizing the different solid state structures adopted by these compounds despite very closely related substituents on the heterocyclic nitrogen atom. An original crisscross organization within dimerized chains is observed with R=NMe2 , differing however from the analogous iPr derivative by a 180° rotation of the heterocyclic nitrogen substituent. On the other hand, the cyclopropyl and n-propyl substituents lead to robust, uniform, non-dimerized chains with a strongly 1 D electronic structure and a formal half-filled electronic structure. The semiconducting behaviour of these two radical complexes is characteristic of a Mott insulator, whose sensitivity to external pressure has been evaluated up to 2.5 GPa.

Conformational behavior, redox and spectroscopic properties of gold dithiolene complexes: [Au(iPr-thiazYdt)2]−1 (Y = O, S, Se)

Three monanionic gold dithiolene complexes with different exocyclic chalcogen atoms (O, S, Se) on the N-isopropyl-1,3-thiazoline-2-chalcogenone-4,5-dithiolate ligand, have been synthetized with the aim of modulating their properties. Due to the presence of the isopropyl (iPr) group in the plane of the thiazoline-2-chalcogenone ring, different syn and anti rotamers can exist, in solution and in the solid state. Characterization of these complexes by spectroscopic and electrochemical methods was carried out in order to investigate the influence of the size, electronegativity and polarizability of the exocyclic chalcogen atom. The molecular structure of the three anionic complexes [Au(iPr-thiazYdt)2]−1, with Y=O, S, Se, were established by single crystal X-ray diffraction studies. Theoretical calculations carried out at the DFT levels were realized on the three possible rotamers, syn/syn, syn/anti and anti/anti of the trans-[Au(iPr-thiazYdt)2]−1 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.

A Single-Component Conductor Based on a Radical Gold Dithiolene Complex with Alkyl-Substituted Thiophene-2,3-dithiolate Ligand.

Alkyl-substituted thiophene-2,3-dithiolate ligands are prepared through a Thio-Claisen rearrangement of 4,5-bis(propargylthio)-1,3-dithiole-2-thione derivatives. The two novel dithiolate ligands, namely, 4,5-dimethyl-thiophene-2,3-dithiolate (α-Me2tpdt) and 4-ethyl-5-methyl-thiophene-2,3-dithiolate (α-EtMetpdt), are engaged in anionic Au(III) square planar complexes formulated as [Au(α-Me2tpdt)2](-) and [Au(α-EtMetpdt)2](-), isolated as Ph4P(+) salts. Monoelectronic oxidation gives the neutral radical complexes [Au(α-Me2tpdt)2](•) and [Au(α-EtMetpdt)2](•). The latter crystallizes into uniform stacks with limited interstack interactions, giving rise to a calculated half-filled band structure. It exhibits a semiconducting behavior with room temperature conductivity of 3 × 10(-3) S cm(-1), indicating that this single-component conductor can be described as a Mott insulator. The different structures observed in [Au(α-EtMetpdt)2](•) and the known [Au(Et-thiazdt)2](•) complex (Et-thiazdt: N-ethyl-thiazoline-2-thione-4,5-dithiolate), despite their very similar shapes, are tentatively attributed to differences in the electronic structures of the ligand skeleton.

Synthesis and characterization of the gold dithiolene monoanion, (Bu4N)[Au(pdt = 2,3-pyrazinedithiol)2

We report the first synthesis and isolation of the gold dithiolene complex (Bu4N)[Au(pdt=2,3-pyrazinedithiol)2]. We characterize this complex using X-ray crystallography, infrared spectroscopy, cyclic voltammetry, and UV–Vis spectroscopy. The title complex is structurally similar to other gold dithiolene complexes. We find that the monoanion and dianion are linked by a reversible electrochemical event, but electrochemical generation of other redox states are irreversible processes. Generation of the dianion and protonation of the monoanion lead to reversible changes in the UV–Vis spectroscopy – primarily for the HOMO−1→LUMO transition.

Molecular Alloys of Neutral Gold/Nickel Dithiolene Complexes in Single-Component Semiconductors.

Control of band filling or doping of molecular (semi)conductors can be performed by substitutional insertion of molecules with a similar shape but a different electron count, with one more or one less electron. This strategy has been explored here within the semiconducting, single-component, radical gold dithiolene complex [AuOC4] bearing para-butoxyphenyl substituents. Alloying with the corresponding neutral nickel dithiolene complex [NiOC4] lacking one electron afforded a complete isostructural series [NiOC4]1-x[AuOC4]x, spanning the whole composition range from x = 0 to x = 1 by 0.1 increments, further characterized by X-ray diffraction and EDX analyses. Magnetic susceptibility data confirm the antiferromagnetic interactions between neighboring radical gold dithiolene complexes. The electrical conductivity increases exponentially with the x gold fraction, while the activation energy remains constant in the more conducting, gold-rich samples. This behavior is tentatively assigned to the tunneling barriers of variable width (with x) but of constant height, separating more conducting gold-rich segments. Comparison of redox potentials for the 1e(-) oxidation and reduction of both [NiOC4] and [AuOC4] dithiolene complexes indicates that the [NiOC4] nickel complex does not act as a dopant for the radical [AuOC4] complex.

Hydrogen-bonding interactions in a single-component molecular conductor: a hydroxyethyl-substituted radical gold dithiolene complex.

The anionic hydroxyethyl-substituted gold dithiolene complex [NEt4][Au(EtOH-thiazdt)2] is synthesized and further oxidized to the neutral radical species [Au(EtOH-thiazdt)2](•) through electrocrystallization. Single-crystal X-ray diffraction studies highlight the existence of the two cis and trans isomers for the monoanionic complex, with involvement of the hydroxy group in intermolecular O-H···S hydrogen-bonding interactions. The neutral radical complex, [Au(EtOH-thiazdt)2](•), is isostructural with its known ethyl analogue, namely, [Au(Et-thiazdt)2](•). It exhibits a semiconducting behavior (σRT = 0.05-0.07 S cm(-1)) at room temperature and ambient pressure with an activation energy of 0.14 eV. Comparison of the crystal structures and transport and magnetic properties with those of the prototypical [Au(Et-thiazdt)2](•) single-component conductor shows that the replacement of ethyl by a slightly bulkier hydroxyethyl substituent affects only weakly the overlap interactions, complemented here by added O-H···S hydrogen-bonding interactions.

Theoretical and experimental investigations on the nonlinear optical properties of gold(III) dithiolene complexes

Degenerate four-wave mixing (DFWM) experiments have been performed to determine the third-order nonlinear optical (NLO) susceptibilities (χ(3)) of gold(III) maleimide dithiolate tetraphenylphosphonium, (PPh4)[Au(midt)2], (Au-P) and gold(III) maleimide dithiolate melamine melaminium hybrid solvate, (C3N6H6)(C3N6H7+)[Au(midt)2]−·2DMF·2H2O, (Au-Mel). Ab-initio quantum mechanical calculations (time-dependent Hartree–Fock (TDHF) method) of Au-P and Au-Mel have been carried out to compute the electric dipole moment (μ), the dispersion-free and frequency-dependent dipole polarizability (α) and the second hyperpolarizability (γ) values. These theoretical calculations are in good agreement with the experimentally obtained results by the DFWM technique. All the investigations show clearly the effect played by the counter ion on the resulting NLO properties of the two gold complexes.

Nonlinear optical response of a symmetrical Au dithiolene complex under ps and ns laser excitation in the infrared and in the visible

In the present study new results are reported concerning the nonlinear optical response of a gold dithiolene complex, namely the [Au(dpedt) 2]. The nonlinear optical properties of the dithiolene are investigated using 35 ps and 4 ns laser excitation, both in the infrared (1064 nm) and in the visible (532 nm), by means of the Z-scan technique. In all cases, the nonlinear optical absorption coefficient β, the nonlinear refraction parameter γ′ and the third-order susceptibility χ (3) have been determined and the second hyperpolarizability γ was obtained. The present results are discussed and compared with previously reported data of similar dithiolene complexes.

Probing magnetic interactions in columnar phases of a paramagnetic gold dithiolene complex

A novel radical gold dithiolene complex exhibits a hexagonal columnar mesophase, as confirmed by optical microscopy, DSC analysis and X-ray diffraction. The extent of delocalization of the spin density in such a complex was analyzed by EPR. Temperature dependent magnetization measurements reveal that the global magnetic moment is remarkably affected at the liquid-crystalline phase transition with a marked hysteresis signature, rare behavior among the few described paramagnetic discotic phases. In addition, these molecules were found to strongly aggregate in solution into one-dimensional fibers with a mean diameter of 60 nm extending over micrometres, leading to the formation of gel-like structures. These fibers are stable and can be isolated on surfaces. The gelation of the system can also be detected by temperature-dependent magnetic measurements.

The layered topology of a five components melaminium-melamine hybrid salt of a functional gold(iii) dithiolene complex

We report the synthesis, characterization and structures of the tetraphenylphoshonium salt of the (maleimide dithiolato)gold(III) complex, (PPh4)+[AuIII(midt)2]−, 1 and the charge-assisted assembly of a gold(III) maleimide dithiolate melamine (mel, 2,4,6-triamino-1,3,5-triazine) melaminium hybrid solvate, (Hmel)+(mel)[Au(midt)2]−·2DMF·2H2O, 2. Compounds 1 and 2 both crystallize in the triclinic P space group. The structure of 1 is identical to that of the one-electron oxidized, paramagnetic complex, (PPh4)+[NiII(midt)2]− reported previously. A non-reversible oxidation wave is observed upon anodic scans at 0.84 V/SCE corresponding to the couple [AuIII(midt)2]1−/0, demonstrating that neutral gold dithiolene complexes of electron poor ligands are not stable. The structure of 2 consists of puckered supramolecular layers. Within one layer, all –NH, –NH2 and O–H hydrogen bond donors are engaged with all available hydrogen bond acceptors, namely the oxygen atoms of the gold dithiolene anion, the dimethylformamide and the water molecules as well as the nitrogen atoms of the triazine cores. A salient feature of this pattern of association is the identification of a [Hmel]+–[mel]–[midt] motif engaging one neutral melamine molecule with one end of one maleimide dithiolate (midt) gold complex ligand, although the opposite midt ligand is not involved in the same motif. Hence, it is remarkable that a [mel]–[midt] motif is stabilized despite the availability of the melaminium cation to be engaged in a direct interaction which would have enhanced the electrostatics of the system. In turn, a dual [Hmel]+–[mel] motif prevails, in effect pulling the ions apart within the layer, directing a pattern of interaction by which the Madelung energy of this ionic solid is effectively reduced.

Chiral, Neutral, and Paramagnetic Gold Dithiolene Complexes Derived from Camphorquinone

AbstractReaction of racemic (dl)‐ or enantiopure (D)‐camphorquinone with P4S10in dimethylimidazolidinone followed by addition of NiCl2·6H2O or KAuCl4affords the corresponding bornylenedithiolato metal complexes [(dl‐bordt)2Ni], [(D‐bordt)2Ni], [(dl‐bordt)2Au], and [(D‐bordt)2Au] in their neutral form. Cyclic voltammetry and UV/Vis/NIR spectrometry show that the bornylenedithiolato ligand acts as a highly electron‐rich dithiolene ligand. Complete assignment of the1H and13C NMR signals of the diamagnetic enantiopure [(D‐bordt)2Ni] is reported thanks to a combination of 2D NMR spectroscopy experiments. X‐ray crystal structure determinations were performed for the four complexes, showing that the two diastereomeric mixtures, [(dl‐bordt)2Ni] and [(dl‐bordt)2Au], are isomorphous (space groupP21/c), as are also the two enantiopure complexes, [(D‐bordt)2Ni] and [(D‐bordt)2Au] (space groupP21). Positional disorder of the two (D)‐ and (L)‐bornylenedithiolate enantiomers on the same position is observed in the structure of the diastereomeric mixtures, with the complex located on the inversion center. The temperature dependence of the magnetic susceptibility of the paramagnetic gold complexes [(dl‐bordt)2Au] and [(D‐bordt)2Au] demonstrates the presence of antiferromagnetic interactions, to a larger extent in the diastereoisomeric mixture [(dl‐bordt)2Au] than in the enantiopure complex [(D‐bordt)2Au], as a consequence of stronger lateral S···S intermolecular interactions in the former. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Amphiphilic paramagnetic neutral gold dithiolene complexes

The sulfiding of benzils with P(4)S(10) in 1,3-dimethyl-2-imidazolidinone (DMI) as solvent allows for a direct synthesis of neutral radical, gold dithiolene complexes based on 1,2-bis-(4-alkoxy-phenyl)ethylene-1,2-dithiolate ligands with n-butyl, n-octyl and n-dodecyl chains. The three neutral and soluble complexes Au-OC(4), Au-OC(8) and Au-OC(12) exhibit a near infrared (NIR) absorption band around 1.5 mum and EPR characteristics which confirm a strong delocalization of the spin density on the electron-rich dithiolene ligands. X-Ray crystal structures of Au-OC(4) and Au-OC(12) are compared with those of the corresponding nickel complexes. They are characterised by segregation of the alkyl chains into layered structures with a stacking of the radical complexes into alternated spin chains, confirmed by the temperature dependence of the magnetic susceptibility which attests for antiferromagnetic interactions and a singlet ground state. Observations under polarising microscope and DSC experiments do not reveal a thermotropic behaviour for Au-OC(12).

Perylene salts of unsymmetrical nickel and gold dithiolene complexes with 3 ? 2 stoichiometry: conformational polymorphism and strong antiferromagnetic interactions

The square-planar AuIII complex of the unsymmetrical tfadt dithiolate ligand (tfadt: 2-(trifluoromethyl)acrylonitrile-1,2-dithiolate) is found to exhibit conformational polymorphism in its n-Bu4N+ salt, as both cis and trans isomers were found to crystallize separately in the same crystallization batch. Electrocrystallization of perylene in the presence of the diamagnetic [n-Bu4N][Au(tfadt)2] or the paramagnetic (S = 1/2) [n-Bu4N][Ni(tfadt)2] nickel analog affords isostructural salts with an unusual 3 ∶ 2 stoichiometry, that is [Per]3[M(tfadt)2]2 (M = Au, Ni), with an alternation of dicationic [Per]32+ perylene triads and dianionic [M(tfadt)2]22− dithiolene complex dyads within one-dimensional chains. These salts are characterized by strong antiferromagnetic interactions within perylene triads and [Ni(tfadt)2]22− dyads and an essentially diamagnetic behaviour.

Fluorine Segregation Controls the Solid-State Organization and Electronic Properties of Ni and Au Dithiolene Complexes: Stabilization of a Conducting Single-Component Gold Dithiolene Complex

Electrooxidation of the nickel dithiolene complex [Ni(F2pdt)2]–· (F2pdt2-: 6,6-difluoro-6,7-dihydro-5H-[1,4]dithiepine-2,3-dithiolato) affords the corresponding neutral complex [Ni(F2pdt)2]0 whose layered structure is highly reminiscent, albeit not isostructural, of that of the isosteric fluorinated bis(propylenedithio)tetrathiafulvalene and characterized by a segregation of the fluorinated moieties into fluorous bilayers. The gold neutral complex [Au(F2pdt)2]·, which is isostructural with the fluorinated bis(propylenedithio)tetrathiafulvalene, was prepared by electrocrystallization of the [n-Bu4N][Au(F2pdt)2] salt. [Au(F2-pdt)2]· is a semiconductor with high room temperature conductivity. The origin of this semiconducting behavior as well as possible guidelines in order to realize metallic conductivity in gold dithiolene neutral molecular solids are discussed.

Magnetic and electrical properties of new aromatic 1,2-dithiolato-Au(III) and Au(IV) complexes

Three new materials containing aromatic dithiolene complexes of gold have been prepared. In one of these compounds, the crystals consist of neutral radicaloid complexes formally containing Au(IV), while in the two other, the gold complexes serve as electron donating counterions to organic radicalcations; TTF and dibenzo-TTF respectively. The electrical and magnetic properties has been investigated. All three compounds are semiconductors with low activation energies. The neutral gold-dithiolene complex exhibits reduced magnetic spin-susceptibility compared to the calculated paramagnetic susceptibility for one spin per molecule.