Homoleptic Molybdenum Cluster Sulfides Functionalized with Noninnocent Diimine Ligands: Synthesis, Structure, and Redox Behavior

Evolution of the Electronic Structure of the trans-[Re6S8bipy4Cl2] Octahedral Rhenium Cluster during Reduction

Understanding the processes that occur during the redox transformations of complexes coordinated by redox-active apical ligands is important for the design of electrochemically active compounds with functional properties. In this work, a detailed analysis of the interaction energy and electronic structure was performed for cluster complexes trans-[Re₆S₈bipy₄Cl₂]ⁿ (n = 2-, 4-, 6-, 8-), which can be obtained by stepwise electrochemical reduction of a neutral cluster trans-[Re₆S₈bipy₄Cl₂] in DMSO solution. It was shown that the formation of open-shell paramagnetic ions with S = 1, 2 and 1 is the most energetically favorable for n = 2-, 4- and 6-, respectively.

A Sterically Hindered Derivative of 2,1,3-Benzotelluradiazole: A Way to the First Structurally Characterised Monomeric Tellurium-Nitrogen Radical Anion

Interaction of the tetradentate redox-active 6,6'-[1,2-phenylenebis(azanediyl)]bis(2,4-di-tert-butylphenol) (H₄ L) with TeCl₄ leads to neutral diamagnetic compound TeL (1) in high yield. The molecule of 1 has a nearly planar TeN₂ O₂ fragment, which suggests the formulation of 1 as Te^II L^2- , in agreement with the results of DFT calculations and QTAIM and NBO analyses. Reduction of 1 with one equivalent of [CoCp₂ ] leads to quantitative formation of the paramagnetic salt [CoCp₂ ]⁺ [1]^.- , which was characterised by single-crystal XRD. The solution EPR spectrum of [CoCp₂ ]⁺ [1]^.- at room temperature features a quintet due to splitting on two equivalent ¹⁴ N nuclei. Below 150 K it turns into a broad singlet line with two weak satellites due to the splitting on the ¹²⁵ Te nucleus. Two-component relativistic DFT calculations perfectly reproduce the a(¹⁴ N) HFI constants and A_∥ (¹²⁵ Te) value responsible for the low-temperature satellite splitting. Calculations predict that the additional electron in 1^.- is localised mainly on L, while the spin density is delocalised over the whole molecule with significant localisation on the Te atom (≥30 %). All these data suggest that 1^.- can be regarded as the first example of a structurally characterised monomeric tellurium-nitrogen radical anion.

A biradical oxo-molybdenum complex containing semiquinone and o-aminophenol benzoxazole-based ligands

We report a new mononuclear molybdenum(iv) complex, MoOLBISLSQ, in which LSQ (2,4-di-tert-butyl o-semibenzoquinone ligand) has been prepared from the reaction of the o-iminosemibenzoquinone form of a tridentate non-innocent benzoxazole ligand, LBIS, and MoO2(acac)2. The complex was characterized by X-ray crystallography, elemental analysis, IR and UV-vis spectroscopy and magnetic susceptibility measurements. The crystal structure of MoOLBISLSQ revealed a distorted octahedral geometry around the metal centre, surrounded by one O and two N atoms of LBIS and two O atoms of LSQ. The effective magnetic moment (μ eff) of MoOLBISLSQ decreased from 2.36 to 0.2 μB in the temperature range of 290 to 2 K, indicating a singlet ground state caused by antiferromagnetic coupling between the metal and ligand centred unpaired electrons. Also, the latter led to the EPR silence of the complex. Cyclic voltammetry (CV) studies indicate both ligand and metal-centered redox processes. MoOLBISLSQ was applied as a catalyst for the oxidative cleavage of cyclohexene to adipic acid and selective oxidation of sulfides to sulfones with aqueous hydrogen peroxide.

WS2 /MoS2 Heterostructures through Thermal Treatment of MoS2 Layers Electrostatically Functionalized with W3 S4 Molecular Clusters

The preparation of 2D stacked layers combining flakes of different nature gives rise to countless numbers of heterostructures where new band alignments, defined at the interfaces, control the electronic properties of the system. Among the large family of 2D/2D heterostructures, the one formed by the combination of the most common semiconducting transition metal dichalcogenides, WS₂ /MoS₂ , has awakened great interest owing to its photovoltaic and photoelectrochemical properties. Solution as well as dry physical methods have been developed to optimize the synthesis of these heterostructures. Here, a suspension of negatively charged MoS₂ flakes is mixed with a methanolic solution of a cationic W₃ S₄ -core cluster, giving rise to a homogeneous distribution of the clusters over the layers. In a second step, a calcination of this molecular/2D heterostructure under N₂ leads to the formation of clean WS₂ /MoS₂ heterostructures, where the photoluminescence of both counterparts is quenched, proving an efficient interlayer coupling. Thus, this chemical method combines the advantages of a solution approach (simple, scalable, and low-cost) with the good quality interfaces reached by using more complicated traditional physical methods.

Synthesis of [Mo3S4] Clusters from Half-Sandwich Molybdenum(V) Chlorides and Their Application as Platforms for [Mo3S4Fe] Cubes

Triangular [Mo₃S₄] clusters are known to serve as platforms to accommodate a metal atom M, furnishing cubic [Mo₃S₄M] clusters. In this study, three [Mo₃S₄] clusters supported by η⁵-cyclopentadienyl (Cp^R) ligands, [Cp^R₃Mo₃S₄]⁺ (Cp^R = C₅Me₄SiMe₃, C₅Me₄SiEt₃, and C₅Me₄H), were synthesized via half-sandwich molybdenum chlorides Cp^RMoCl₄. In the cyclic voltammogram of the [Mo₃S₄] cluster having C₅Me₄H ligands, a weak feature appeared in addition to the [Cp^R₃Mo₃S₄]^0/- redox process, indicating the interaction between [Cp^R₃Mo₃S₄]^- and the [NⁿBu₄] cation of the electrolyte, while such a feature was less significant for the C₅Me₄SiR₃ variants. The [Mo₃S₄] clusters with bulky C₅Me₄SiR₃ ligands were successfully applied as platforms to accommodate an Fe atom to furnish cubic [Mo₃S₄Fe] clusters. On the other hand, the corresponding reactions of the less bulky C₅Me₄H analogue gave complex mixtures.

Investigation of electronic structure of tri- and tetranuclear molybdenum clusters by X-ray photoelectron and emission spectroscopies and quantum chemical methods

Charge state studies of compounds [Mo₃S₄(tu)₈(H₂O)]Cl₄·4H₂O (1), [Mo₃S₄Cl₃(dbbpy)₃]Cl·5H₂O (2), [Mo₃S₄(CuCl)Cl₃(dbbpy)₃][CuCl₂] (3), containing {Mo₃S₄}⁴⁺ and {Mo₃CuS₄}⁵⁺ cluster cores bearing terminal thiourea (tu) or 4,4'-di-tert-butyl-2,2'-bipyridine (dbbpy) ligands, have been performed by X-ray photoelectron and X-ray emission spectroscopies combined with quantum chemical calculations. The best agreement between theory and experiments has been obtained using the B3LYP method. According to the experimental and calculated data, the Mo atoms are in the oxidation state 4+ for all compounds. The energies and shapes of the Cu2p lines indicate formal oxidation states of Cu as 1+. The coordination of Сu(I) to the cluster {Mo₃S₄} in 3 does not lead to significant changes in the charge state of the molybdenum atoms and the {Mo₃S₄} unit can be considered as a tridentate metallothia crown ether.

Hemilability of phosphine-thioether ligands coordinated to trinuclear Mo3S4 cluster and its effect on hydrogenation catalysis

Phosphine-thioether ligands were coordinated to the Mo₃S₄ cluster to afford [Mo₃S₄Cl₃(PS)₃]⁺ complexes. Their catalytic activity in nitrobenzene reduction reflects the different hemilabile behaviours of PS1, PS2 and PS3.

Kinetics Aspects of the Reversible Assembly of Copper in Heterometallic Mo3CuS4 Clusters with 4,4'-Di-tert-butyl-2,2'-bipyridine

Treatment of the triangular [Mo₃S₄Cl₃(dbbpy)₃]Cl cluster ([1]Cl) with CuCl produces a novel tetrametallic cuboidal cluster [Mo₃(CuCl)S₄Cl₃(dbbpy)₃][CuCl₂] ([2][CuCl₂]), whose crystal structure was determined by X-ray diffraction (dbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine). This species, which contains two distinct types of Cu(I), is the first example of a diimine-functionalized heterometallic M₃M'S₄ cluster. Kinetics studies on both the formation of the cubane from the parent trinuclear cluster and its dissociation after treatment with halides, supported by NMR, electrospray ionization mass spectrometry, cyclic voltammetry, and density functional theory calculations, are provided. On the one hand, the results indicate that addition of Cu(I) to [1]⁺ is so fast that its kinetics can be monitored only by cryo-stopped flow at -85 °C. On the other hand, the release of the CuCl unit in [2]⁺ is also a fast process, which is unexpectedly assisted by the CuCl₂^- counteranion in a process triggered by halide (X^-) anions. The whole set of results provide a detailed picture of the assembly-disassembly processes in this kind of cluster. Interconversion between trinuclear M₃S₄ clusters and their heterometallic M₃M'S₄ derivatives can be a fast process occurring readily under the conditions employed during reactivity and catalytic studies, so their occurrence is a possibility that must be taken into account in future studies.

Synthesis, structure and NMR studies of trinuclear Mo3S4 clusters coordinated with dithiophosphate and chiral carboxylate ligands

Introducing chirality into the Mo₃S₄ cluster has been achieved through coordination of (S)-mandelate and (S)-phenyllactate ligands affording new complexes as a pair of diastereoisomers, (PS) and (MS), represented in the scheme.

Cycloaddition of alkynes to diimino Mo3S4 cubane-type clusters: a combined experimental and theoretical approach

Newly synthesised molibdenum diimino clusters interact with alkynes leading to dithiolene species.

Synthesis and optical power limiting properties of heteroleptic Mo3S7 clusters

Substitution of the halide ligands in (Bu4N)2[Mo3S7X6] (X = Cl, Br) by diimine ligands, such as 4,4'-dimethyl-2,2'-bipyridine (dmbpy), 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen), affords the neutral heteroleptic clusters Mo3S7Cl4(dmbpy) (), Mo3S7Br4(dmbpy) (), Mo3S7Br4(bpy) (), and Mo3S7Br4(phen) (). Further substitution of the halide ligands in Mo3S7Br4(diimine) clusters by dmit (1,3-dithiole-2-thione-4,5-dithiolate) allows the preparation of the mixed diimine-dithiolene neutral cluster complexes Mo3S7(dnbpy)(dmit)2 (, dnbpy = 4,4'-dinonyl-2,2'-bipyridine), Mo3S7(dcmbpy)(dmit)2 (, dcmbpy = 4,4'-dimethoxycarbonyl-2,2'-bipyridine), and Mo3S7(dcbpy)(dmit)2 (, dcbpy = 2,2'-bipyridine-4,4'-dicarboxylic acid). The optical limiting properties of complexes have been assessed by the open-aperture Z-scan technique at 570 nm, employing a nanosecond optical parametric oscillator. In order to investigate the effect of increasing the π-system, complexes , with the general formula Mo3S7X4(diimine), (X = Cl, Br), were compared to clusters , containing the dmit ligand. The influence of the metal content on the optical power limiting properties was also investigated by comparing the trinuclear series of complexes prepared herein with the bis(dithiolene) dinuclear cluster (Et4N)2[Mo2O2S2(BPyDTS2)2], which has been recently prepared by our group. All trinuclear clusters are efficient optical limiters (σeff > σ0) with the threshold limiting fluence F15% decreasing on proceeding from dinuclear to trinuclear clusters and, generally, on extending the π-system.