Metal Dithiolene Research Articles

Photodissociation of Bis(S-benzyl-1,2-diphenyl-1,2-ethylenedithiolato)metal (Ni, Pd, Pt) Complexes

Bis(S-benzyl-1,2-diphenyl-1,2-ethylenedithiolato)metal (Ni,Pd,Pt) (1a−c) complexes are known to undergo photochemical reactions that produce the corresponding neutral free metal dithiolene M(S2C2Ph2)2 (3a−c) complexes in solution. The reaction mechanisms of these photoreactions were examined by means of EPR and UV/vis absorption techniques. In the first step of the reaction the photodissociation of a C−S bond occurs to yield one benzyl radical and the monobenzyl dithiolene complex radical (2a−c). Both radicals were observed by time-resolved electron paramagnetic resonance (TREPR). The benzyl radical was also trapped by TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl). Analysis of the TREPR signals shows that the radicals are produced from the excited triplet states of 1a−c within 100 ns. From the analyses of time-resolved and steady state EPR data, and absorption spectra, the intermediate complex radicals (2a−c) were assigned as [M(S2C2Ph2){S2(CH2Ph)C2Ph2}] (M = Ni, Pd, Pt). Spin densities on the central metals were determined from their anisotropic g values and hyperfine coupling constants by comparing the data with those of [M(S2C2Ph2)2]-. A correlation between the spin density and the decay time of the intermediate complexes (2a−c) was pointed out. The second step of the reaction was found to be the dissociation of a second benzyl substituent, which occurs in the dark. The reaction rate was discussed in terms of the spin density (ρM) on the metal and the S−C(benzyl) bond order (ρsρc)1/2 of the intermediate radicals, 2a−c.

Syntheses and properties of the nickel complexes of 1,2-dithiolates MEDT and PHDT. The crystal structure of [Bu 4N][Ni(MEDT) 2

The syntheses and characterizations of the nickel(III) complexes, [Bu 4N] [Ni(MEDT) 2] (MEDT = 5-methyl-6-hydro-1,4-dithiin-2,3-dithiolate) and [Bu 4N] [Ni(MEDT) 2] (MEDT = 5-phenyl-6-hydro-1,4-dithiin-2,3-dithiolate) are reported. Both complexes show characteristic IR and UV-vis absorptions of transition metal dithiolate complexes. The cyclic voltammograms contain two waves, indicating a two-step electrochemical process [ML 2] 0 = [ML 2] 1− = [ML 2] 2−. The solid powder ESR spectra show three broad signals. The frozen glass ESR spectra yielded g value assignments of g 1 = 2.102, g 2 = 2.049 and g 3 = 2.004 for [Ni(MEDT) 2] − and g 1 = 2.104, g 2 = 2.048 and g 3 = 2.004 for [Ni(PHDT) 2] −. Both complexes are semiconductors with electrical conductivities of the order of 10 −8 S cm −1. Single-crystal structure analysis revealed that the gross geometry of the [Ni(MEDT) 2] − anion is planar with the exception of the external unit —CH 2CH(Me)—. There are two different kinds of anions. The anions form stacks along the b- and c-axes. The nearest intermolecular SS distance is 5.104 Å.

Third order NLO properties of PMMA films co-dispersed with metal dithiolene oligomers

Metal dithiolene oligomers show enhanced third order NLO properties compared with films containing monomeric metal complexes.

Charge‐Transfer‐Komplexe von Metalldithiolenen, XVIII. Ionenpaare von Dithiolencobaltaten mit Bipyridinium‐Akzeptoren

Charge‐Transfer Complexes of Metal Dithiolenes, XVIII. – Ion Pairs of Dithiolene Cobaltates with Bipyridinium AcceptorsIon pair charge‐transfer (IPCT) complexes of the type {A2+[Co(mnt)2]2−}, mnt2− = cis‐1,2‐dicyano‐1,2‐ethenedithiolate, A2+ = a bipyridinium derivative, posses IPCT bands in the range from 590 to 950 nm. An X‐ray structure analysis of {BQ2+[Co(mnt)2]2−}, BQ2+ = 6,7,8,9‐tetrahydrodipyrido[1,2‐a:2,1‐c][1,4]diazocinium, reveals that the strongly twisted acceptor and planar donor do not form mixed stacks, as usually observed in less twisted systems. Electrical conductivities of pressed powder pellets are in the range of 10−15 to 10−7 Ω−1 cm−1 and do not exhibit a simple correlation with the driving force of electron transfer between the ion pair components. The cis‐trans isomerization of an ethene‐bridged methyl viologen acceptor leaves the conductivity almost unchanged.

Oxidation‐state‐dependent conformation in Cp*Mo(dmit) and antiferromagnetic ordering (TN = 8 K) of the neutral 17‐electron complex Cp*Mo(dmit)

Metal dithiolene complexes are attractive for the development of novel materials with extended electronic properties. The preparation of Cp*Mo(dmit)2⊖ and its investigation by cyclic voltammetry, antiferromagnetic resonance, and electron paramagnetic resonance are described. Complexes of this class, i.e., with heteroatom substitution on the dmit dithiolene ligand, are shown to exhibit conformational flexibility directly related to the orbital occupancy.

Raman excitation profiles of metal dithiolenes: Comparison between the transform method and time‐dependent theory

AbstractThe time‐dependent theory of the resonance Raman effect was employed for the calculation of the Raman excitation profiles and optical absorption spectra of the meial dithiolene species [Zn(dmit)2]2− and [Ni(dmit)2]2− (dmit = 4,5‐dimercapto‐1,3‐dithiolc‐2‐thionc) The model adopted takes into account the three normal modes notable for their enhancement at resonance, and embodies the linear non‐Condon coupling contribution. Previous calculations for these species using the transform method lead to estimates of the relative displacements of potential surface minima for the three modes considered, while the present calculations led to absolute values for such displacements. The metal‐sulphur bond length is increased by 0.016 and 0.027 Å in the zinc and nickel complexes, respectively.

Novel Dithiolene Complexes and Tetrathiafulvalenes

Abstract Novel dithiolene metal complexes, some of which absorb in the near infrared, and tetrathiafulvalenes, in particular tetraiodotetrathia- fulvalene, have been prepared, and their magnetic properties studied.

Syntheses, properties and structures of copper and nickel complexes of 6,7‐dihydro‐5H‐1,4‐dithiepin‐2,3‐dithiolate

AbstractThe reaction of CuCl2·2H2O or NiCl2·6H2O with K2(C5H6S4) [potassium salt of 6,7‐dihydro‐5H‐1,4‐dithiepin‐2,3‐dithiolate] under nitrogen atmosphere resulted in the isolation of [Cu(C5H6S4)2]− or [Ni(C5H6S4)2]− as the tetrabutylammonium salt. Both complexes show characteristic IR and UV −Vis absorptions of transition metal dithiolenes. Cyclic voltammograms contain two waves indicating a two step electrochemical procedure [M(C5H6S4)2]0 = [M(C5H6S4)2]1‐= [M(C5H6S4)2]2‐ Single crystal structure study has been carried out on the nickel complex. Crystal of [Bu4N][Ni(C5H6S4)2] belongs to monoclinic space group P21/c with a=17.576(5), b=10.883(2), c=17.773(4) A, β=91.07(2)°, Z=4, and ρ(calcd.)=1.348 g/cm3. Final result is R=0.059 for 2959 reflections. The NiS4 core exhibits square planar coordination with average Ni—S bond length of 2.134(5) Å. There are not anion pairs in crystal. The anions stack along a and c axes while the cations intercalate in them. The nearest S—S contact is 4.429 Å. The solid powder ESR spectrum of the nickel complex shows three broadening signals at g1 =2.097, g2=2.042, g3=2.022. Magnetic susceptibility data for [Bu4N][Ni(C5H6S4)2] reveal enhanced anti‐ferromagnetic interaction.

Charge‐Transfer‐Komplexe von Metalldithiolenen, XIII. cis‐trans‐Photoisomerisierbare Viologene als redoxaktive Akzeptoren —Synthese und elektrische Leitfähigkeit

Charge‐Transfer Complexes of Metal Dithiolenes, XIII[1]. ‐ cis‐trans‐Photoisomerisable Viologens as Redoxactive Acceptors — Synthesis and Electrical ConductivityIon Pair Charge‐Transfer (IPCT) complexes of the type [A2+[ML2]2−} (1a‐f to 4a‐f) are synthesized from dianionic metal dithiolenes [M = Ni, Zn, L = cis‐1,2‐dicyano‐1,2‐ethene‐dithiolate (mnt2−), 2‐thioxo‐1,3‐dithiol‐4,5‐dithiolate (dmit2‐)] and dicationic viologens [A2+ = 4,4′‐(1,2‐ethenediyl)bis(1‐alkylpyridinium)]. The acceptors can exist as cis/trans isomers and may have coordinating properties in the case of 1‐cyanoalkyl groups. The IPCT bands are in the range of 500 to 1200 nm and their energy follows the Hush‐Marcus relation. For the nickel complexes the reorganization energy amounts to 73, for the zinc compounds to 115 kJ/mol. As shown by X‐ray analysis of {A2+[Ni(mnt)2]2−} (2d), A2+ = trans‐4,4′‐(1,2‐ethenediyl)‐bis[1‐(3‐cyanopropyl)pyridinium], the structure consists of stacks of alternating donors and acceptors with a typical plane‐to‐plane distance of 350 pm. There is no interaction between the cyano group of the acceptor and the nickel atom of the donor. The electrical conductivities of the nickel compounds are in the range of 5 · 10−6 to 3 · 10−11 Ω−1 cm−1, and the corresponding activation energies vary from 0.24 to 0.61 eV. For the dmit complexes these values agree well with the free activation enthalpy of the electron transfer reaction A2+ + [ML2]2− → A+ + [ML2]− calculated from the Hush‐Marcus model. This suggests that charge carrier generation occurs by electron transfer. When a trans acceptor is replaced by its cis isomer in [A2+[NiL2]2−}, conductivity changes from 5 · 10−7 to 5 · 10−6 Ω−1 cm−1 and the activation energy from 0.43 to 0.24 eV, when L ‐ dmit2− but stays at about 1 · 10−8 Ω−1 cm−1 for L = mnt2−.

Synthesis of the first diferrocenyl–dithiolene metal complex: bis(ferrocenylethylene-1,2-dithiolato) nickelate(II)

The synthesis and solution redox properties of the first diferrocenyl–dithiolene metal complex, bis(ferrocenylethylene-1,2-dithiolato) nickelate(II) are reported together with the X-ray crystal structure of the ligand precursor, 4-ferrocenyl-1,3-dithiole-2-one.

Characterization of Cure Profile of Anaerobic Adhesives by Real-Time FT-IR Spectroscopy. I. Effect of Transition Metal Dithiolate Complexes

Abstract A model acrylic adhesive formulation consisting of triethylene glycol dimethacrylate (TRIEGMA) monomer, cumene hydroperoxide (CHP), o-benzoic sulfimide (saccharin or BS) and with or without a metal dithiolate catalyst has been made to study kinetics and mechanism of the anaerobic polymerization. In these studies, a real-time FT-IR spectroscopic (RT/FT-IR) technique has been used to study anaerobic cure profiles at room temperature. The catalytic effect of several transition metal dithio complexes for redox-initiated acrylate polymerization has been studied. The dithiolates used in these studies include the dithiocarbamate, xanthate dithiophosphate complexes of copper, nickel and zinc systems. Copper diacetylacetonate was also studied for comparison of its catalytic reactivity. A syner-gistic effect of copper dithiolate catalyst and saccharin was observed. The effects of catalyst concentration, metal and ligand type, and co-initiator on cure profiles have been monitored in a real-time mode.

Charge-transfer in ion pairs: design of photoreactivity in solution and electrical dark- and photoconductivity in the solid

Weak supramolecular charge-transfer interactions within 1:1 ion pair complexes composed of anionic metal dithiolenes and cationic bipyridinium compounds have astonishing consequences on solution and solid state properties. In solution the relation between thermal and optical electron transfer can be analyzed in terms of the Hush-model. Irradiation of the dissolved complexes induces an electron transfer to molecular oxygen which can be quantitatively controlled by proper selection of the acceptor redox potential. The electrical conductivity of pressed powder pellets is quantitatively predictable within the range of 10 −11 to 10 −4 Ω −1cm −1 from the solution redox potentials of the components or from the activation energy of thermal electron transfer calculated from the Hush-model. Finally, the action spectrum of the photoconductivity exhibits a maximum in the range of the optical charge-transfer band.

Charge-transfer complexes of metal dithiolenes. IX. Photoinduced electron transfer within metal dithiolene-viologen ion pairs studied by flash photolysis

Laser flash excitation of 1/1 ion pairs consisting of the reversible redox systems [M(mmt) 2 ] 2- (mnt 2- =maleonitriledithiolate) and V n+ (V=2,2'- or 4,4'-bipyridinium derivative, n=2,1) affords the electron-transfer products [M(mmt) 2 ] - and V (n-1)+ in the case of M=Pt, while no transients are observed when M=Ni. These primary redox products recombine by a fast second-order back-reaction. The cage escape efficiencies are very sensitive to the charge of the quenchers (1.0 for n=1, 0.1 for n=2)

EPR spin flip transitions in some metal dithiolenes

Small line widths (Δ B pp ≅ 0.25–0.40 mT) in the EPR spectra of 63 Cu 2+ in the matrices of some transition metal dithiolenes permit the observation of not-so-easily realizable proton spin flip transitions even at room temperature and at low microwave power. These transitions, studied in four different lattices as a function of crystal orientation, microwave power and temperature, have been found to be from the protons of the counter ions and a few ångströms away from the unpaired electron-containing metal centre. It has been possible to identify the protons and estimate their distances from the metal centre by two different methods. A temperature-dependent evaluation of the distance parameters as well as the observation of the “double” and “triple” flips are reported. The differential saturation of the “main” and “satellite” (due to spin flip) lines studied by the CW saturation method has provided information on the mechanism of spin relaxation in these systems.

Insertion of transition metals into the phosphorus-phosphorus bond of 1,2-dihydro-1,2-diphosphetes: toward the phosphorus analogs of metal dithiolene complexes

The insertion of NiL 2 (L=phosphine) into the P-P bond of 1,2,3,4-tetraphenyl-1,2-dihydro-1,2-diphosphete has been achieved via two methods. In the first, the P-P bond is initially cleaved with lithium and the derivatized dianion allowed to react with [NiCl 2 L 2 ]. The yields primarily a nickeladiphospholene with a distorted square-planar geometry.

The nature of the electronic transitions in some metal dithiolenes as revealed by resonance Raman spectroscopy and transform methods

The nature of the electronic transitions present in the optical spectra of the 4,5-dimercapto-1,3-dithiole-2-thione (H 2dmit) complexes [Ni(dmit) 2] 2− and [Zn(dmit) 2] 2− was investigated by resonance Raman spectroscopy, supported by the transform method. The previous assignment proposed for the 515 nm band in [Zn(dmit) 2] 2− is shown to be incorrect, and the intrinsically different nature of the charge-transfer transitions in [Zn(dmit) 2] 2− and [Ni(dmit) 2] 2− is revealed by the excitation profiles and by the parameters obtained from the use of the transform method.

Photoconductivity of Ion Pair Charge-Transfer (IPCT)

Abstract The results of photoelectric measurements in salts of planar complexes of mono- and dianionic metal dithiolenes with a variety of cations, such as 2, 2′ ‐ and 4,4′-bipyridinium derivatives, are described. It is shown that by specific combinations of ligands, metals, anionic charges and cations photoconductivity gain and spectral response to specific wavelength regions can be tailored. On the basis of ion pair charge-transfer (IPCT) mechanism a model is given according to which photoconductivity of metal dithiolene complexes may be attributed to the photoinduced “reverse” charge‐transfer between anionic and cationic sites resulting in conducting anionic stacks of mixed‐valence.

Metal dithiolene complexes for all‐optical switching devices

Optical data storage, transmission, and handling will require a means to carry out all‐optical switching of information if semiconductor‐based electronics are not to become a serious bottle‐neck for the technology. The various materials which aree being examined wiith a view of this application are reviewed are some recent progress made with metal dithiolene complexes (see figure) described. magnified image

Extended bis-aryldithiolene nickel complexes: Near infrared absorbing compounds

Eleven new bis-aryldithiolene nickel complexes have been synthesised to examine their electronic absorbance properties. They include a new type of chromophore based upon extended bis-aryldithiolene nickel complexes incorporating either 1,2,4,5-tetrathiolbenzene, 1,2,4,5-tetrathiol-3,6-dichloro-benzene or 1,2,4,5-tetrathiol-3,6-difluorobenzene as a ligand. The new complexes based upon the tetrathiol ligand possessed broad near infrared absorbance at energies lower than those of previously reported metal dithiolenes.

Cationic dithiolene metal complexes with 5,6-dihydro-1,4-dithiin-2,3-dithiol: Highly conducting metal complex analogues of BEDT-TTF salts

A new class of highly conducting compounds (cationic dithiolene metal complexes of Ni and Au with 5,6-dihydro-1,4-dithiin-2,3-dithiol (DDDT), which are metal complex analogues of BEDT-TTF salts) has been obtained. The crystal structure of one of the representatives of this class, [Ni(DDDT) 2] 3(BF 4) 2, has been determined. The crystal contains stacks of [Ni(DDDT) 2] cations with shortened intra- and interstack S·S contacts. The conductivity of these complexes at room temperature is 1 – 50 ohm −1 cm −1.