A Family of Oxo-Chalcogenide Molybdenum and Tungsten Complexes, (n-Bu4N)2[M2O2(μ-Q)2(1,3-dithiole-2-thione-4,5-dithiolate)2] (M = Mo, W; Q = S, Se): New Synthetic Entries, Structure, and Gas-Phase Behavior

Screening of biological properties of MoV2O2S2- and MoV2O4-based coordination complexes: Investigation of antibacterial, antifungal, antioxidative and antitumoral activities versus growing of Spirulina platensis biomass

This paper deals with the biological potential of coordination compounds based on binuclear core [Mo^V₂O₂E₂]²⁺ (E = O or S) coordinated with commercially available ligands such as oxalates (Ox^2-), L-cysteine (L-cys^2-), L-histidine (L-his^-), Iminodiacetate (IDA^2-), Nitrilotriacetate (HNTA^2- or NTA^3-) or ethylenediamine tetraacetate (EDTA^4-) by means of various in vitro assays in a screening approach. Results suggest that the obtained complexes show weak antibacterial and antifungal properties while not being cytotoxic on cancerous and mammalian cells. In contrast, [Mo₂O₂E₂(L-cys)₂]^2- complexes stand out as powerful antioxidant, whereas [Mo₂O₂E₂(EDTA)]^2- associating tetraphenylphosphonium counter-cations display strong antibiotic activity. Finally, some complexes have evidenced a positive activity towards the growing of spirulina platensis together with a modification of the proportions of biological components inside the cells. These findings reveal promising bioactivity of the bridged binuclear Mo^(+V) cores inside complexes and encourage further research for new highly active yet non-toxic molecules for biological and biomedical applications.

Reaction Chemistry of the syn-[Mo2O2(μ-S)2(S2)(DMF)3] Complex with Cyanide and Catalytic Thiocyanate Formation

Removal of cyanide as nontoxic thiocyanate under physiological conditions may serve as a catalytic detoxification route in vivo. Aqueous catalytic reaction conditions were explored where at the conditions employed the reaction proceeded to exhaustion in 1 h. The complex, syn-[Mo₂O₂(μ-S)₂(S₂)(DMF)₃] 1, participates in a ligand exchange reaction of the dimethylformamide ligands and cyanide. Simultaneous sulfur abstraction reaction from the terminal disulfide group forms thiocyanate and terminal sulfido ligand. Respective reaction rates for the two reactions appear competitive where different products were isolated solely based on change of reaction temperature. The approach to determine the number of cyanide ligands participating in the ligand exchange reaction by varying the stoichiometry and reaction temperature led to identification and isolation of tetranuclear complexes 2 and 5 and dinuclear complexes 3, 4, and 6. A synthesized and fully characterized thiocyanate analog of 6 (7) supports spectroscopic characterization of 6. The tetranuclear anion, [Mo₄O₄(μ-S)₆(CN)₄]^4-, 2, was crystallized from a reaction at ambient temperature. The dinuclear anion, [Mo₂O₂(μ-S)₂(S)(CN)₃]^3-, 3, was crystallized from similar reaction conditions at lower temperature. The reaction yield of thiocyanate obtained at pH of 7.4 and at 9.2 as a function of time, for several ratios of cyanide, favors the sulfur abstraction reaction at elevated pH. The sulfur abstraction reaction is the first step in a proposed mechanism of the reaction of cyanide and thiosulfate to form thiocyanate and sulfite by 1.

On the Critical Effect of the Metal (Mo vs. W) on the [3+2] Cycloaddition Reaction of M3 S4 Clusters with Alkynes: Insights from Experiment and Theory

Whereas the cluster [Mo3 S4 (acac)3 (py)3 ](+) ([1](+) , acac=acetylacetonate, py=pyridine) reacts with a variety of alkynes, the cluster [W3 S4 (acac)3 (py)3 ](+) ([2](+) ) remains unaffected under the same conditions. The reactions of cluster [1](+) show polyphasic kinetics, and in all cases clusters bearing a bridging dithiolene moiety are formed in the first step through the concerted [3+2] cycloaddition between the C≡C atoms of the alkyne and a Mo(μ-S)2 moiety of the cluster. A computational study has been conducted to analyze the effect of the metal on these concerted [3+2] cycloaddition reactions. The calculations suggest that the reactions of cluster [2](+) with alkynes feature ΔG(≠) values only slightly larger than its molybdenum analogue, however, the differences in the reaction free energies between both metal clusters and the same alkyne reach up to approximately 10 kcal mol(-1) , therefore indicating that the differences in the reactivity are essentially thermodynamic. The activation strain model (ASM) has been used to get more insights into the critical effect of the metal center in these cycloadditions, and the results reveal that the change in reactivity is entirely explained on the basis of the differences in the interaction energies Eint between the cluster and the alkyne. Further decomposition of the Eint values through the localized molecular orbital-energy decomposition analysis (LMO-EDA) indicates that substitution of the Mo atoms in cluster [1](+) by W induces changes in the electronic structure of the cluster that result in weaker intra- and inter-fragment orbital interactions.

Surfactant-thermal method to synthesize a novel two-dimensional oxochalcogenide

A new two-dimensional (2D) oxosulfide, (N2H4)2Mn3Sb4S8(μ3-OH)2 (1), has been successfully synthesized under surfactant-thermal conditions with hexadecyltributylphosphonium bromide as the surfactant. Compound 1 has a layered structure and contains a novel [Mn3(μ3-OH)2]n chain along the b-axis. The photocatalytic activity for compound 1 has been demonstrated under visible-light irradiation and continuous H2 evolution was observed. Our results indicate that surfactant-thermal synthesis could be a promising method for growing novel crystalline oxochalcogenides with interesting structures and properties.

Dithiolene dimetallic molybdenum(V) complexes displaying intraligand charge transfer (ILCT) emission

Bifunctional dithiolene ligands have been coordinated to the Mo(V)(O)(μ-S2)Mo(V)(O) unit to afford [Mo2O2(μ-S)2(BPyDTS2)2](2-) (1(2-)) (BPyDTS2 (2-bis-(2-pyridyl)methylene-1,3-dithiolene) dianions. Reaction of the 1(2-) molybdenum dimer with pentacarbonylchlorothenium(i) affords a tetrametallic complex of formula [Mo2O2(μ-S)2(BPyDTS2)2{Re(CO)3Cl}2](2-) (2(2-)). The monomeric (CH3)2Sn(BPyDTS2) (3) tin complex has also been prepared for comparative purposes. In the structure of (Et4N)2[1], the two metal atoms are in a square pyramidal coordination environment defined by two bridging sulfur atoms, one terminal oxygen atom and the two sulfur atoms of the bifunctional dithiolene ligand. This arrangement leaves two nitrogen atoms on each side which coordinate to two Re atoms in the 2(2-) tetrametallic complex. Compound 3 has a distorted tetrahedral structure defined by two carbon atoms of the methyl groups and two sulfur atoms of the dithiolene ligand. The luminescence properties of all three complexes in acetonitrile have been investigated. Detailed studies supported on quantum mechanical calculations revealed that complex 1(2-) shows photoluminescence in the 600-800 nm region with a maximum wavelength of 628 nm and an emission quantum yield of 0.092, associated with an intraligand charge transfer (ILCT) transition. Coordination of two Re(CO)3Cl fragments to 1(2-) to afford 2(2-) does not affect the emission spectrum and shape although it decreases the quantum yield, approximately by a factor of 4.6. Compound 3 exhibits a similar emission spectrum to those of the complexes 1(2-) and 2(2-) in good agreement with the ILCT assignment. The quantum yield of 3 lies between that of the 1(2-) and 2(2-) complexes.

The dithiolene ligand and tetrathiafulvalene precursor molecules 4,5-bis(bromomethyl)-1,3-dithiol-2-one and 4,5-bis[(dihydroxyphosphoryl)methyl]-1,3-dithiol-2-one

The crystal structures of 4,5-bis(bromomethyl)-1,3-dithiol-2-one, C(5)H(4)Br(2)OS(2), (I), and 4,5-bis[(dihydroxyphosphoryl)methyl]-1,3-dithiol-2-one, C(5)H(8)O(7)P(2)S(2), (II), occur with similar unit cells in the same monoclinic space group. Both molecules reside on a twofold symmetry axis coincident with the C=O bond, so that the substituents in the 4- and 5-positions project above and below the plane of the 1,3-dithiol-2-one ring. In both structures, the molecules align themselves in a head-to-tail fashion along the b axis, and these rows of molecules then stack, with alternating directionality, along the c axis. For (II), an extensive network of intermolecular hydrogen bonds occurs between molecules within the same stack and between adjacent stacks. Each -CH(2)P(O)(OH)(2) group participates in four hydrogen bonds, twice as donor and twice as acceptor.

Sulfur-based redox reactions in Mo3S7(4+) and Mo3S4(4+) clusters bearing halide and 1,2-dithiolene ligands: a mass spectrometric and density functional theory study

The gas phase fragmentation reactions of sulfur-rich [Mo(3)S(7)Br(6)](2-) (1(2-)), [Mo(3)S(7)(bdt)(3)](2-) (2(2-)), and [Mo(3)S(4)(bdt)(3)](2-) (3(2-)) (bdt = benzenedithiolate) complexes have been investigated by electrospray ionization (ESI) tandem mass spectrometry and theoretical calculations at the density functional theory level. Upon collision induced dissociation (CID) conditions, the brominated 1(2-) dianion dissociates through two sequential steps that involves a heterolytic Mo-Br cleavage to give [Mo(3)S(7)Br(5)](-) plus Br(-) followed by a two-electron redox process that affords [Mo(3)S(5)Br(5)](-) and diatomic S(2) sulfur. Dianion [Mo(3)S(7)(bdt)(3)](2-) (2(2-)) dissociates through two sequential redox processes evolving diatomic S(2) sulfur and neutral bdt to yield [Mo(3)S(5)(bdt)(3)](2-) and [Mo(3)S(5)(bdt)(2)](2-), respectively. Conversely, dianion [Mo(3)S(4)(bdt)(3)](2-) (3(2-)), with sulfide instead of disulfide S(2)(2-) bridged ligands, remains intact under identical fragmentation conditions, thus highlighting the importance of disulfide ligands (S(2)(2-)) as electron reservoirs to trigger redox reactions. Regioselective incorporation of (34)S and Se at the equatorial position of the Mo(3)S(7) cluster core in 1(2-) and 2(2-) have been used to identify the product ions along the fragmentation pathways. Reaction mechanisms for the gas-phase dissociation pathways have been elucidated by means of B3LYP calculations, and a comparison with the solution reactivity of Mo(3)S(7) and Mo(3)S(4) clusters as well as closely related Mo/S/dithiolene systems is also discussed.

Synthesis, characterization and structure of a low coordinate desoxomolybdenum cluster stabilized by a dithione ligand

Using an oxidized state of a dithiolene ligand, diisopropylpiperazine-2,3-dithione (i-Pr(2)Pipdt), two monooxo-molybdenum complexes have been synthesized. From one of them, a desoxomolybdenum cluster, [(i-Pr(2)Pipdt)Mo](4)[BF(4)](4) has been prepared. The molecular structure of this cluster reveals metal-metal interactions and weak coordination by the BF(4) anion.

A combined stopped-flow, electrospray ionization mass spectrometry and31P NMR study on the acetic acid-mediated fragmentation of the hydroxo-chalcogenide cluster [W3Se4(OH)3(dmpe)3]+(dmpe = 1,2-bis(dimethylphosphanyl)ethane) to yield the dinuclear [W2Se2(µ-Se)2(µ-CH3CO2)(dmpe)2]+complex

The reaction of the incomplete-cuboidal [W(3)Se(4)(OH)(3)(dmpe)(3)](+) ([1](+)) cluster with acetic acid in acetonitrile solution leads to cluster fragmentation with formation of the dinuclear [W(2)Se(2)(mu-Se)(2)(mu-CH(3)CO(2))(dmpe)(2)](+) ([2](+)) complex. The X-ray structure of [2]PF(6) presents two equivalent metal centres bridged by one acetate ligand. Each W atom is additionally coordinated by one terminal selenium atom, two bridging selenido and two diphosphane phosphorus atoms in an essentially octahedral environment. Stopped-flow and conventional UV-vis studies indicate that fragmentation of [1](+) into [2](+) occurs through a complex mechanism. Three steps can be distinguished in the stopped-flow time scale, all of them showing a first order dependence with respect to the acetic acid concentration, followed by very slow spectral changes that lead to the formation of [2](+). Phosphorus NMR, electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS/MS) have been used to identify the nature of the reaction intermediates formed in the different steps. These studies indicate that the first two steps correspond to the formal substitutions of the hydroxo ligands at two metal centres by terminal acetate ligands. The third step involves bridging of one of the terminal acetate ligands, which actually prepares the trinuclear cluster to afford the acetate-bridged [W(2)Se(2)(mu-Se)(2)(mu-CH(3)CO(2))(dmpe)(2)](+) ([2](+)) complex. Although the precise details of the final conversion to [2](+) have not been established, the results obtained by combination of the different experimental techniques provide a complete picture of the speciation of the cluster [1](+) in acetonitrile solutions containing acetic acid.