Metal Dithiolene Research Articles

Light-Induced Control of the Spin Distribution on Cu⁻Dithiolene Complexes: A Correlated Ab Initio Study.

Metal dithiolene complexes—M(dmit)2—are key building blocks for magnetic, conducting, and optical molecular materials, with singular electronic structures resulting from the mixing of the metal and dmit ligand orbitals. Their use in the design of magnetic and conducting materials is linked to the control of the unpaired electrons and their localized/delocalized nature. It has been recently found that UV–Vis light can control the spin distribution of some [Cu(dmit)2]−2 salts in a direct and reversible way. In this work, we study the optical response of these salts and the origin of the differences observed in the EPR spectra under UV–Vis irradiation by means of wave function-based quantum chemistry methods. The low-lying states of the complex have been characterized and the electronic transitions with a non-negligible oscillator strength have been identified. The population of the corresponding excited states promoted by the UV–Vis absorption produces significant changes in the spin distribution, and could explain the changes observed in the system upon illumination. The interaction between neighbor [Cu(dmit)2]−2 complexes is weakly ferromagnetic, consistent with the relative orientation of the magnetic orbitals and the crystal packing, but in disagreement with previous assignments. Our results put in evidence the complex electronic structure of the [Cu(dmit)2]−2 radical and the relevance of a multideterminantal approach for an adequate analysis of their properties.

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.

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.

Construction of three-dimensional anionic molecular frameworks based on hydrogen-bonded metal dithiolene complexes and the crystal solvent effect

Three-dimensional hydrogen-bonded anionic molecular frameworks based on a metal dithiolene complex were constructed with a significant solvent effect.

Vibrational Control of Covalency Effects Related to the Active Sites of Molybdenum Enzymes.

A multitechnique spectroscopic and theoretical study of the Cp2M(benzenedithiolato) (M = Ti, V, Mo; Cp = η5-C5H5) series provides deep insight into dithiolene electronic structure contributions to electron transfer reactivity and reduction potential modulation in pyranopterin molybdenum enzymes. This work explains the magnitude of the dithiolene folding distortion and the concomitant changes in metal-ligand covalency that are sensitive to electronic structure changes as a function of d-electron occupancy in the redox orbital. It is shown that the large fold angle differences correlate with covalency, and the fold angle distortion is due to a pseudo-Jahn-Teller (PJT) effect. The PJT effect in these and related transition metal dithiolene systems arises from the small energy differences between metal and sulfur valence molecular orbitals, which uniquely poise these systems for dramatic geometric and electronic structure changes as the oxidation state changes. Herein, we have used a combination of resonance Raman, magnetic circular dichroism, electron paramagnetic resonance, and UV photoelectron spectroscopies to explore the electronic states involved in the vibronic coupling mechanism. Comparison between the UV photoelectron spectroscopy (UPS) of the d2 M = Mo complex and the resonance Raman spectra of the d1 M = V complex reveals the power of this combined spectroscopic approach. Here, we observe that the UPS spectrum of Cp2Mo(bdt) contains an intriguing vibronic progession that is dominated by a "missing-mode" that is composed of PJT-active distortions. We discuss the relationship of the PJT distortions to facile electron transfer in molybdenum enzymes.

(Invited) Conductive Metal Dithiolene MOFs for Electrocatalytic Applications

The development of efficient and inexpensive catalysts capable of solar-to-fuel energy conversion is vital for mitigating the adverse effects of carbon-based fuels on the environment and meeting the rising global energy demand. Heterogenization of molecular catalysts onto electrodes is an attractive strategy to combine the advantageous properties of homogeneous and heterogeneous catalysis. MOFs have emerged as a promising class of materials; however, their insulating nature has limited their application as electrocatalysts. We have demonstrated the successful integration of metal dithiolene units into one and two-dimensional frameworks by using dinucleating and trinucleating thiolate-based ligand scaffolds. The developed metal dithiolene frameworks display remarkable activity for the electrocatalytic conversion of water into hydrogen and electrical conductivity that is switchable from semiconducting to metallic. We expect the design principles discovered in these studies to have a profound impact towards the development of advanced materials and sustainable technologies.

Electrolyte Effect on Electrocatalytic Hydrogen Evolution Performance of One-Dimensional Cobalt–Dithiolene Metal–Organic Frameworks: A Theoretical Perspective

Discovering inexpensive and earth-abundant electrocatalysts to replace the scarce platinum group metal-based electrocatalysts holds the key for large-scale hydrogen fuel generation, which relies heavily on the theoretical understanding of the properties of candidate materials and their operating environment. The recent applications of the cobalt–dithiolene complex as promising electrocatalysts for the hydrogen evolution reaction have been broadened by forming low-dimensional metal–organic frameworks (MOFs) through polymerization. Using the Gibbs free energy of the adsorption of hydrogen atoms as a key descriptor, S atoms within one-dimensional MOFs are identified to be the preferred catalytic site for HERs. Our theoretical results further reveal that the activities of part S atoms can be improved by interacting with alkali metal cations from the electrolytes; specifically, the influence of cations on the performance is dependent on the electron affinity of cations. Our theoretical findings, therefore, demonstrate that the selection of electrolytes can be a promising approach to enhance the performance of electrocatalysts for HERs.

What Happens Without Nickel? Cyclization Reactions of Ethylene with Ethanedithial and Related Molecules.

We present a computational study of the mechanism of the formation of 6-member heterocycles through the binding of ethylene to oxaldehyde, ethanedithial, and 2-thioxoacetaldehyde. This process is related to the olefin separation technology by metal dithiolenes and dioxolenes, being the formation of those heterocycles the main decomposition route. We also present a benchmark of 26 density functionals (spanning hybrid, double-hybrid, range-separated, semilocal, and local functionals) related to CCSD(T)/CBS reference values. Both the cyclization reaction and the isomerization of the cyclic product are included in the benchmark. The best functional among those tested for these reactions is ωB97XD, and the effect of the basis set is also investigated for it. © 2017 Wiley Periodicals, Inc.

Static and Dynamic Electron Correlation in the Ligand Noninnocent Oxidation of Nickel Dithiolates.

Metal dithiolates have a wide range of applications from catalysis to molecular conductors with the ligands being the source of electrons during electrochemical oxidation in an effect known as ligand noninnocence. Recent large-scale variational two-electron reduced-density matrix (2-RDM) calculations of the vanadium oxo complex and manganese superoxide dismutase show that quantum entanglement stabilizes the addition of an electron to the ligands, providing a quantum mechanical explanation for ligand noninnocence. In this paper, we confirm and explore the ligand noninnocence in the electron oxidation series of bis(ethylene-1,2-dithiolato)nickel or [Ni(edt2)](-2,-1,0) with variational 2-RDM calculations. While previous wave function calculations of this series have selected only the ligand π orbitals as the critical (active) orbitals to be correlated, we find that both ligand π and nickel d orbitals must be correlated to generate a realistic picture of the electron-transfer process. Using the computed 2-RDM to seed a solution of the anti-Hermitian contracted Schrödinger equation, we predict that the singlet state is lower in energy than the triplet state, which is consistent with experimental observations.

Thiophene‐Extended Nickel Thiazoledithiolene: π‐Extended Fused‐Ring Metal Dithiolenes with Stabilized Frontier Orbitals

The preparation of tetrabutylammonium bis[2‐(2‐thienyl)‐4,5‐thiazoledithiolato]nickelate(1–) is presented as the first example of a new family of π‐extended fused‐ring metal dithiolenes. The optical, electronic, and structural properties of this complex have been characterized by UV/Vis‐NIR spectroscopy, cyclic voltammetry, and X‐ray crystallography. Comparison of these properties to the analogous nickel thiophenedithiolene shows that incorporation of nitrogen into the fused ring stabilizes the frontier orbitals of the thiazole‐based complex, while preserving the planar geometry, electronic delocalization, and low‐energy NIR absorption of the previous thiophene‐based species.

Spin-polarized transport properties in some transition metal dithiolene complexes.

Spin filtering materials are of great current interest in part due to their applications in molecular electronics. In this study, we carried out a theoretical investigation on the charge transport properties of transition metal (TM) dithiolene complexes with TM = Ni, Fe and Mn by using non-equilibrium Green's function/density functional theory (NEGF-DFT) methods. The characteristics of current-voltage and spin-resolved transmission spectra pointed out that Ni complexes are non-polarized, while Fe and Mn complexes exhibit high polarization and can be regarded as excellent candidates for spin-filtering materials with high spin-filtering efficiency. These differences were rationalized on the basis of electron delocalization over the molecular junction of the partial distribution of α- and β-spin molecular projected self-consistent Hamiltonian (MPSH) orbitals, and also the first eigenchannels of molecular junctions.

Triplet state CPL active helicene-dithiolene platinum bipyridine complexes.

Chiral metal dithiolene complexes represent a family of chiral precursors, which can give rise to molecular materials with properties resulting from the interplay of chirality with conductivity, magnetism, and photophysics. We describe herein the first examples of chiral metal diimine dithiolene complexes, by the use of a platinum(ii) centre coordinated by 2,2'-bipyridine and helicene-dithiolene ligands. The straightforward synthesis of racemic and enantiopure complexes allows the preparation of luminescent Pt(bipy) [4] and [6]helicene compounds for which the solid-state structure was determined as well. TD-DFT calculations support the assignment of the low-energy bands observed in the UV-vis absorption spectra as mixed metal-ligand-to-ligand charge transfer transitions and confirm that the emission band results from the T1 excited state. Interestingly, the enantiopure [6]helicene complexes show CPL activity at room temperature in acetonitrile solutions with an anisotropy factor of 3 × 10-4.

A computational investigation into the catalytic activity of a diselenolene sulfite oxidase biomimetic complex

Molybdenum is the only 4d metal found in almost all life. One such molybdenum-containing enzyme is sulfite oxidase, which also contains the dithiolene-molybdopterin ligand. Sulfite oxidase is essential in the degradation of sulfur-containing compounds such as cysteine and methionine. Past work has shown parallels in the chemistry of dithiolene–metal and diselenolene–metal complexes. Thus, in this present work, the oxygen atom transfer mechanism for a diselenolene sulfite oxidase biomimetic complex was investigated using computational tools, the results of which were compared to the analogous dithiolene biomimetic complex. From the results obtained, the molybdenum-diselenolene sulfite oxidase biomimetic complex is able to catalyse the oxygen atom transfer and does so with a marginally lower value of ΔrG‡than that for the analogous dithiolene complex. In particular, it was found that on average, the diselenolene complex had an activation energy 1.2 kJ mol–1lower in energy than the analogous dithiolene complex. However, the calculated value of ΔrG suggests that the oxidation of sulfite is more favourable for the dithiolene complex where the average difference in reaction aqueous Gibbs reaction energy was –9.4 kJ mol–1relative to the diselenolene complex. It is noted that with the use of D3 and D3BJ corrections in combination with the B3LYP functional, the barrier for oxygen atom transfer is lowered by more than 30.0 kJ mol–1for both the diselenolene and dithiolene complexes. Such results suggest that to study such oxo-transfer reactions, the proper treatment of dispersion interaction is necessary.

A regular nanostructured dithiolene metal complex film for ultrasensitive biosensing of liver enzyme

A novel ultrasensitive biosensor was constructed by the [TBA]2[Ni(mnt)2]/graphene (mnt=maleonitriledithiolate) composite film for the detections of glutamate and alanine aminotransferase (ALT). The [TBA]2[Ni(mnt)2] nanocubes with a dimension of 500nm were in-situ crystallized on the surface of Au electrode modified using thiol graphene in advance. Due to the synergistic effect between the electrocatalysis of [Ni(mnt)2]2− anion and the excellent conductivity of graphene, the as-prepared biosensors showed remarkably reversible electrochemical redox and stability. It exhibited high sensitivities of 27.32μAmM−1cm−2 and 0.636nAμM−1 for the biosensing of glutamate and ALT with the corresponding wide linear ranges of 10–600μM−1 and 5–140UL−1, respectively. This high performance ALT biosensor is promising application in the trace analysis of more physiological substances, and the successful adoption of [TBA]2[Ni(mnt)2] material in the biosensor construction can arouse more dithiolene metal complexes in the further application of electrocatalysis.

Cation‐anion radical interactions between halopyridinium cations and metal dithiolene complexes [M(C2S2)2CN]−•: A theoretical study of halogen bonds in conducting or magnetic molecular materials

AbstractMetal dithiolene complexes have been extensively used for the elaboration of conducting or magnetic materials, whose molecular arrangements can be sensitively influenced by strong and directional noncovalent interactions. In this work, halogen bonds between N‐methyl‐3‐halopyridinium cations and cyano‐substituted anion radicals, [M(C2S2)2CN]−• (M = Ni, Pd, and Pt), were systematically investigated at the M06 level of theory. The CN···X interactions in these systems are predicted to be considerably strong and play a vital role in the controlling of the crystal structures of molecular conductors and magnets. The electrostatics contributes mainly to the attraction of these halogen bonds, while the orbital interaction is also important. Particularly, the formation of these interactions has little effect on the distribution of SOMOs, which is strongly delocalized on the two dithiolene moieties. These results will assist in the design of functional materials that exhibit exotic conducting or magnetic properties.

Steady-State Spectroscopic Analysis of Proton-Dependent Electron Transfer on Pyrazine-Appended Metal Dithiolenes [Ni(pdt)2], [Pd(pdt)2], and [Pt(pdt)2] (pdt = 2,3-Pyrazinedithiol).

We report the structural, electronic, and acid/base properties of a series of ML2 metal dithiolene complexes, where M = Ni, Pd, Pt and L = 2,3-pyrazinedithiol. These complexes are non-innocent and possess strong electronic coupling between ligands across the metal center. The electronic coupling can be readily quantified in the monoanionic mixed valence state using Marcus-Hush theory. Analysis of the intervalence charge transfer (IVCT) band reveals that that electronic coupling in the mixed valence state is 5800, 4500, and 5700 cm(-1) for the Ni, Pd, and Pt complexes, respectively. We then focus on their response to acid titration in the mixed valence state, which generates the asymmetrically protonated mixed valence mixed protonated state. For all three complexes, protonation results in severe attenuation of the electronic coupling, as measured by the IVCT band. We find nearly 5-fold decreases in electronic coupling for both Ni and Pt, while, for the Pd complex, the electronic coupling is reduced to the point that the IVCT band is no longer observable. We ascribe the reduction in electronic coupling to charge pinning induced by asymmetric protonation. The more severe reduction in coupling for the Pd complex is a result of greater energetic mismatch between ligand and metal orbitals, reflected in the smaller electronic coupling for the pure mixed valence state. This work demonstrates that the bridging metal center can be used to tune the electronic coupling in both the mixed valence and mixed valence mixed protonated states, as well as the magnitude of change of the electronic coupling that accompanies changes in protonation state.

Chemical transformation of dithiolene ligands in heteroleptic and homoleptic complexes (M = Ti, Zn, Au)

Heteroleptic and homoleptic dithiolene metal complexes such as Cp2Ti(dithiolene), [Zn(dithiolene)2]2− and [Au(dithiolene)2]−1 complexes have been synthesized from the 1-tertiobutyl-1,3-thiazoline-2-thione-4,5-dithiolate (tBu-thiazdt) dithiolene ligand. The reactivity of these complexes towards iodomethane (MeI) has been examined. Both the titanocene and the gold complexes undergo a transformation of the tBu-1,3-thiazoline-2-thione core to a 2-methylthio-1,3-thiazole one with elimination of the tBu substituent. The reaction of MeI with the Zn complex leads to a tris(thiomethyl)-thiazole derivative due to the alkylation of the sulfur atoms and the decoordination together with the transformation into the thiazole core. Electrochemical, spectral and X-ray diffraction investigations carried out on these various complexes are also presented.

Synthesis, characterization, and crystal structures of molybdenum complexes of unsymmetrical electron-poor dithiolene ligands

Mo(S2C2(CF3)2)3, 1a, has proven a useful p-dopant in organic electronics. To develop more soluble p-dopants, MoS92− was treated with alkynes CF3CCCO2Me and CF3CCCOCF3 to give the dianions of the corresponding tris(dithiolene) complexes, 1b2− and 1c2−, respectively, which were then oxidized to neutral molybdenum tris[1-(methoxycarbonyl)-2-(trifluoromethyl)-ethane-1,2-dithiolene], 1b, and molybdenum tris[1-(trifluoroethanoyl)-2-(trifluoromethyl)ethane-1,2-dithiolene], 1c, using NO+PF6−. The crystal structures of (NEt4+)21b2−, (NEt4+)21c2−, and neutral 1c have been determined. In all three cases, the metal coordination is approximately trigonal prismatic and the major isomer is cis (approximately C3v). The structure of 1b2− is distorted by a twist towards pseudo-octahedral coordination similar to that seen in structures of 1a2− and Mo(S2C2(CO2Me)2)32−, 1d2−, salts, and that of 1c exhibits marked folds between the planes formed by the ligand atoms and those formed by the Mo and coordinated S atoms, similar to those seen in the structure of 1a. On the other hand, the metal dithiolene core of 1c2− is essentially undistorted from C3v symmetry. The oxidant strength of the neutral molecules increases in the order 1d<1b<1a<1c, with the potentials ranging from −0.02 to +0.39V versus the ferrocenium/ferrocene couple.

Selectively detecting Hg2+ – A “mercury quick test” with bis-(coumarin–dithiolene) niccolate

By combining a dithiolene metal binding moiety with coumarin as substituent and nickel as central metal a green complex was developed, which sensitively and selectively indicates the presence of Hg2+ ions in sample solutions by color degrading. Except with eyesight, this effect is also evidenced by UV–Vis spectroscopy in the biologically interesting NIR region, which is unaffected by absorptions of natural material. Other common metal ions as Cu2+, Zn2+, Fe3+ and many more do not interfere with the mercury ion detection. The indicator-complex is air and water stable and an easily applied, ready to use, low cost tool without any need for additional reagents, complicated technical procedures or laborious sample preparation.

Ligand effect on the reactivity difference of Mo Tris(dithiolene) complexes towards Ethylene: A computational study

Dithiolene ligand based additions of ethylene with a series of the Mo tris(dithiolene) complexes were studied by using density functional theory (DFT) methods. Computational results show that both the electronic effect and the ligand distortion come from the substituents of unreacted and reacted dithiolene ligands have significant impact on the reactivity of Mo tris(dithiolene) complexes towards ethylene. The complexes with strong electron withdrawing groups, i.e. –CN and –CF3, introduced at the unreacted ligands can increase the reactivity of reacted dithiolene with ethylene. However, keeping a strong electron withdrawing groups on the unreacted ligands, the cyclized conjugated substituents on the reacted ligand of Mo tris(dithiolene) complexes lead to its higher reactivity with ethylene than other complexes, due to the larger ligand distortion coming from the better interaction between the metal dz2 orbital and the ligand π bonding orbital. Our study shed new light on the ligand effect on the reactivity of metal dithiolene complexes towards simple olefins such as ethylene. These finding are expected to guide the material design for olefin abstraction.