Molybdenum Cluster Compounds Research Articles

Light Emissive Nanocomposites Containing a Blue Fluorescent Dicationic Tetraphenylethene and a Red Phosphorescent [Mo6I8(OCOC2F5)6]2− Octahedral Cluster for Optical Writing

AbstractAn emissive organic–inorganic hybrid material is obtained by a cationic metathesis between a blue fluorescent tetraphenylethylene‐based salt: [TPEIm2]I2, and a red‐NIR phosphorescent octahedral molybdenum cluster compound: Cs2[Mo6I8(OCOC2F5)6]. As demonstrated by Single Crystal X‐Ray Diffraction, the hybrid [TPEIm2][Mo6I8(OCOC2F5)6] crystallizes as a 2:2 dimer and emits in the red‐NIR area. Its emission properties are studied in the solid state and once embedded in poly(methylmethacrylate) by steady state and time dependent photoluminescence spectroscopy. They are further compared to the case in which the two starting salts are directly integrated in the polymer matrix. Obtained nanocomposites show evanescent UV‐2A optical writing and reading behavior, with color contrasts depending on how emitters have been introduced.

Molybdenum-Iodine Cluster Loaded Polymeric Nanoparticles Allowing a Coupled Therapeutic Action with Low Side Toxicity for Treatment of Ovarian Cancer

The ability of cancer cells to develop resistance to anti-cancer drugs, known as multidrug resistance, remains a major cause of tumor recurrence and cancer metastasis. This work explores the double mechanism of toxicity of (D, L-lactide-co-glycolide) acid (PLGA) nanoparticles encapsulating a molybdenum cluster compound, namely Cs2[{Mo6I8}(OOCC2F5)6] (CMIF). Hemocompatibility and biocompatibility assays show the safe potential of CMIF loaded nanoparticles (CNPs) as delivery systems intended for tumor targeting for PDT of ovarian cancer with a slight hemolytic activity and a lack of toxicity up to 50 µM CMIF concentration. Cellular uptake shows a preferential uptake of CNPs in lysosomes, which is not interfering with CMIF activity. The double mechanism of CNPs consists in a production of ROS and a DNA damage activity, from 5 µM and 0.5 µM respectively (CMIF concentration). The cellular death mechanism comprises 80% of necrosis and 20% of direct apoptosis by direct DNA damages. This work confirms CMIF loaded PLGA nanoparticles as an efficient and relevant delivery system for PDT

Heterogeneous photoactive antimicrobial coatings based on a fluoroplastic doped with an octahedral molybdenum cluster compound.

Despite the wide variety of strategies developed to combat pathogenic microorganisms, the infectious diseases they cause remain a worldwide health issue. Hence, the search for new disinfectants, which prevent infection spread, constitutes an extremely urgent task. One of the most promising methods is the use of photoactive compounds - photosensitizers, capable of generating reactive oxygen species, in particular, singlet oxygen (O2(1Δg)), which causes rapid and effective death of microorganisms of all types. In this work, we propose the utilization of the powdered cluster complex (Bu4N)2[{Mo6I8}(OTs)6] as a photoactive additive to commercially available fluoroplastic lacquer F-32L to create heterogeneous self-sterilizing coatings. We show that soaking of the prepared films in water for 60 days did not lead to a decrease in their photosensitization properties indicating their excellent stability. Moreover, the use of the cluster complex in the solid state allowed significant expansion of the operating wavelength range, which covers the UV region and a large part of the visible region (250-650 nm). The films displayed high photoantimicrobial activity against five common pathogens (bacteria and fungi) under white-light irradiation. Overall, the properties demonstrated make these materials promising for practical use in everyday outdoor and indoor disinfection since they are active under both sunlight and artificial lighting.

Octahedral molybdenum clusters as radiosensitizers for X-ray induced photodynamic therapy.

The use of radiosensitizers recently emerged as a promising approach to circumvent the depth penetration limitations of photodynamic therapy of cancer and to enhance radiotherapeutical effects. A widely explored current strategy is based on complex nanoarchitectures that facilitate the transfer of energy harvested from X-ray radiation by scintillating nanoparticles to the surrounding photosensitizer molecules to generate reactive oxygen species, mostly singlet oxygen O2(1Δg). We describe an alternative approach aiming at a considerable simplification of the architecture. The presented nanoparticles, made of the luminescent octahedral molybdenum cluster compound (n-Bu4N)2[Mo6I8(OCOCF3)6], efficiently absorb X-rays due to the high content of heavy elements, leading to the formation of the excited triplet states that interact with molecular oxygen to produce O2(1Δg). The activity of the nanoparticles on HeLa cells was first investigated under UVA/blue-light irradiation in order to prove the biological effects of photosensitized O2(1Δg); there is no dark toxicity at micromolar concentrations, but strong phototoxicity in the nanomolar range. The nanoparticles significantly enhance the antiproliferative effect of X-ray radiation in vitro at lower concentration than for previously reported O2(1Δg) radiosensitizing systems and this effect is more pronounced on cancer HeLa cells than non-cancer MRC cells. The results demonstrate that the cluster-based radiosensitizers of O2(1Δg) have strong potential with respect to the enhancement of the efficacy of radiotherapy with exciting opportunities for cancer treatment.

Solvent-mediated purification of hexa-molybdenum cluster halide, Cs2[Mo6Cl14] for enhanced optical properties

An octahedral molybdenum cluster compound, Cs2[Mo6Cl14], was purified by recrystallization with hydrophilic alcohol solvents for enhancing its luminescence efficiency.

X-ray Inducible Luminescence and Singlet Oxygen Sensitization by an Octahedral Molybdenum Cluster Compound: A New Class of Nanoscintillators.

Newly synthesized octahedral molybdenum cluster compound (n-Bu4N)2[Mo6I8(OOC-1-adamantane)6] revealed uncharted features applicable for the development of X-ray inducible luminescent materials and sensitizers of singlet oxygen, O2((1)Δg). The compound exhibits a red-NIR luminescence in the solid state and in solution (e.g., quantum yield of 0.76 in tetrahydrofuran) upon excitation by UV-vis light. The luminescence originating from the excited triplet states is quenched by molecular oxygen to produce O2((1)Δg) with a high quantum yield. Irradiation of the compound by X-rays generated a radioluminescence with the same emission spectrum as that obtained by UV-vis excitation. It proves the formation of the same excited triplet states regardless of the excitation source. By virtue of the described behavior, the compound is suggested as an efficient sensitizer of O2((1)Δg) upon X-ray excitation. The luminescence and radioluminescence properties were maintained upon embedding the compound in polystyrene films. In addition, polystyrene induced an enhancement of the radioluminescence intensity via energy transfer from the scintillating polymeric matrix. Sulfonated polystyrene nanofibers were used for the preparation of nanoparticles which form stable dispersions in water, while keeping intact the luminescence properties of the embedded compound over a long time period. Due to their small size and high oxygen diffusivity, these nanoparticles are suitable carriers of sensitizers of O2((1)Δg). The presented results define a new class of nanoscintillators with promising properties for X-ray inducible photodynamic therapy.

Water-soluble octahedral molybdenum cluster compounds Na2[Mo6I8(N3)6] and Na2[Mo6I8(NCS)6]: Syntheses, luminescence, and in vitro studies

The octahedral molybdenum cluster compounds Na2[Mo6I8(N3)6] and Na2[Mo6I8(NCS)6] were synthesized and their luminescent properties and biological activity were investigated. Most molybdenum cluster compounds reported so far have had low solubility in water and/or underwent hydrolysis connected with aggregation, sedimentation, and diminishing luminescence and singlet oxygen-sensitizing properties. This behavior prevented the investigation of their photophysical properties and in vitro biological activities in aqueous media. Title compounds behave differently. They are well soluble in water and have red luminescence, which is quenched by oxygen to produce singlet oxygen, O2(1Δg), in high quantum yields. Even though [Mo6I8(N3)6]2− and [Mo6I8(NCS)6]2− gradually hydrolyze to mono-hydroxy derivatives, they do not form sedimenting aggregates, luminescence properties are well-defined, and the quantum yields of O2(1Δg) remain unchanged. These attractive features, suitable for luminescent probes or O2(1Δg) sensitizers in living cells, are overshadowed by the toxicity, especially of [Mo6I8(NCS)6]2−, and by the limited uptake by the HeLa and HEK 293T cell lines.

95Mo Solid-State Nuclear Magnetic Resonance Spectroscopy and Quantum Simulations: Synergetic Tools for the Study of Molybdenum Cluster Materials

The ability of (95)Mo solid-state nuclear magnetic resonance (SSNMR) spectroscopy to probe the atomic and electronic structures of inorganic molybdenum cluster materials has been demonstrated for the first time. Six cluster compounds were studied: MoBr(2), Cs(2)Mo(6)Br(14), (Bu(4)N)(2)Mo(6)Br(14), each containing the octahedral Mo(6)Br(14)(2-) cluster unit, and MoS(2)Cl(3), Mo(3)S(7)Cl(4), and MoSCl that contain metallic dimers, trimers, and tetramers, respectively. To overcome inherent difficulties due to the low sensitivity of (95)Mo SSNMR, both high-magnetic-field spectrometers and the quadrupolar Carr-Purcell Meiboom-Gill sensitivity enhancement pulse sequence under magic-angle-spinning conditions, combined with a hyperbolic-secant pulse were used. Experimental measurements as well as characterization of the (95)Mo electric field gradient and chemical shift tensors have been performed with the help of quantum-chemical calculations under periodic boundary conditions using the projector augmented-wave and the gauge-including projector augmented-wave methods, respectively. A large (95)Mo chemical shift range is measured, ∼3150 ppm, and the isotropic chemical shift of the Mo atoms is clearly correlated to their formal oxidation degree in the various clusters. Furthermore, a direct relation is evidenced between the molybdenum quadrupolar coupling constant and the bond lengths with its surrounding ligands. Our results demonstrate the efficiency of the combined use of quantum-chemical calculations and (95)Mo SSNMR experiments to study inorganic molybdenum cluster compounds.

ChemInform Abstract: An Ionic Liquid Based Single Step Room Temperature Route for the Synthesis of Molybdenum Cluster Compounds.

AbstractThe structures of compounds (IV) and (V) are determined by single crystal XRD.

An Ionic Liquid Based Single Step Room Temperature Route for the Synthesis of Molybdenum Cluster Compounds

AbstractA soft and convenient single step route is developed to synthesize molybdenum cluster compounds using an ionic liquid as reaction medium. Bi[Mo5Cl13]Cl and [BiCl][Mo6Cl14] were isolated from the ionic liquid [BMIM]Cl/AlCl3 ([BMIM]+: 1‐n‐butyl‐3‐methylimidazolium) and characterized. Black, cubic crystals of Bi[Mo5Cl13]Cl are obtained at room temperature by the reaction of bismuth, BiCl3, and MoCl5 in Lewis‐acidic ionic liquid [BMIM]Cl/AlCl3. Bi[Mo5Cl13]Cl crystallizes in the cubic space group Pn$\bar{3}$ with a = 1291.6(3) pm. In the [Mo5Cl13]2– cluster, the molybdenum atoms form a square pyramid with Mo–Mo bond lengths 258.9(2) pm and 259.5(2) pm. The structure is a defect variant of the Pb[Mo6Cl14] type; in statistical distribution one of the molybdenum atoms is missing in the cluster core. The bismuth(III) cations, which are in octahedral coordination by the apical chloride ions of the clusters, connect the cluster anions into a three dimensional network. Light red crystals of monoclinic [BiCl][Mo6Cl14] were obtained by the oxidation of bismuth with MoCl5 in [BMIM]Cl/AlCl3. The structure determination is in excellent agreement with literature data of crystals obtained by high temperature syntheses.

Carbothermal synthesis, spectral and magnetic characterization and Li-cyclability of the Mo-cluster compounds, LiYMo 3O 8 and Mn 2Mo 3O 8

The molybdenum cluster compounds, LiYMo 3O 8 and Mn 2Mo 3O 8 are prepared by the carbothermal reduction method and characterized by various techniques. The FT-IR at ambient temperature (RT), and Raman spectra at various temperatures (78–450 K) are reported for the first time and results are interpreted. Magnetic studies on Mn 2Mo 3O 8 in the temperature range, 10–350 K confirm that it is ferrimagnetic, with T C = 39 K. Magnetic hysteresis and magnetization data at various fields and temperatures are presented. The Li-cyclability is investigated by galvanostatic cycling in the voltage range, 0.005–3.0 V vs. Li at 30 mA/g (0.08 C). LiYMo 3O 8 shows a total first-discharge capacity of 305 ±5 mAh/g whereas the first-charge capacity is only 180 mAh/g at RT. However, both values increased systematically with an increase in the cycle number and yielded a reversible capacity of 385 ±5 mAh/g at the end of 120th cycle. At 50 °C, the reversible capacity is 418 ±5 mAh/g at the 60th cycle. The coulombic efficiency ranges from 94% to 98%. The Li-cyclability behavior of Mn 2Mo 3O 8 is entirely different from that of LiYMo 3O 8. The total first-discharge and charge capacities are 710 ± 5 and 565 ±5 mAh/g, but drastic capacity-fading occurs during cycling. The reversible capacity at the end of 50th cycle is only 205 ±5 mAh/g. Plausible reaction mechanisms are proposed and discussed based on the galavanostatic cycling, cyclic voltammetry, ex situ XRD, ex situ TEM and impedance spectral data.

Cations Insertion in Molybdenum Cluster Compounds: Electronic Structure and Electrochemical Study Using Cavity Microelectrode

Owing to the high lability of cations in the three-dimensional framework of K1+x Mo12S14 (0 ≤ x ≤ 1.6), first-principles calculations and electrochemical methods have been carried out to study the insertion of cations in the empty channels of this compound. The cavity microelectrode that is a suitable electrode for powder material analysis has been used in voltammetric experiments. Results obtained for Li+, Na+, Rb+, K+, Cs+ and NH4 + cations are presented and discussed.

Importance of cluster distortions in the tetrahedral cluster compoundsGaM4X8(M=Mo,V,Nb,Ta;X=S,Se):Ab initioinvestigations

In this paper, we study the structural properties of selected representatives of the so-called molybdenum cluster compounds. Belonging to this family are the $\mathrm{Ga}{M}_{4}{X}_{8}$ compounds with $M=\mathrm{Mo}$ as a group VIB element and V, Nb, or Ta as a group VB element. $X$ denotes either S or Se. These compounds are known to exhibit semiconducting behavior in the electrical resistivity, caused by hopping of electrons between well-separated metal clusters. The large separation of the tetrahedral metal $({M}_{4})$ clusters is believed to be the origin of strong correlations. We show that recent calculations neglected an important type of structural distortion, namely, those happening only within the ${M}_{4}$ unit at a fixed angle $\ensuremath{\alpha}=60\ifmmode^\circ\else\textdegree\fi{}$ of the trigonal (fcc-like) cell. These internal distortions gain a significant amount of energy compared to the cubic cell and they are---to our knowledge---almost undetectable with powder x-ray diffraction experiments. However, they strongly influence the band-structure by opening up a gap at the Fermi-energy. This, however, puts into question whether all compounds of this family are really Mott insulators as stated elsewhere. In particular, ferromagnetic $\mathrm{Ga}{\mathrm{Mo}}_{4}{\mathrm{S}}_{8}$ and $\mathrm{Ga}{\mathrm{V}}_{4}{\mathrm{S}}_{8}$ are well described within density functional theory. Only the Nb- and Ta-based representatives require a large effort due to the lack of magnetic long-range order caused by frustrated antiferromagnetic $M\text{\ensuremath{-}}M$ interactions.

Crystal structures and 31P NMR spectra of two trinuclear molybdenum clusters coordinated by p-chlorobenzoate: Mo 3S 4(DTP) 3( p-ClC 6H 4COO)(Py)·EtOH and Mo 3S 4(DTP) 3( p-ClC 6H 4COO)(DMF)

Two molybdenum cluster compounds, Mo 3S 4(DTP) 3( p-chlorobenzoate)(Py)·EtOH ( I) (DTP=diethyl dithiophosphate) and Mo 3S 4(DTP) 3( p-chlorobenzoate)(DMF) ( II), have been rationally synthesized by the reaction of Mo 3S 4(DTP) 4(H 2O) or Mo 3S 4(DTP) 3(CCl 3COO)(Py) with p-chlorobenzoic acid in different solvents. The crystal structures have been determined by X-ray crystallography. The obviously short Mo2–O (of DMF) distance in ( II) reveals a stronger covalent bond between Mo 3S 4 core and the DMF. 31P NMR studies substantiate that the cluster stability in polar solvents are much improved when μ-DTP or μ-CCl 3COO is replaced by p-chlorobenzoate.

P NMR studies on the ligand dissociation of trinuclear molybdenum cluster compounds

AbstractA series of carboxylate‐substituted trinuclear molybdenum cluster compounds formulated as Mo3S4(DTP)3(RCO2)(L), where R = H, CH3, C2H5, CH2Cl, CCl3, R1C6H4(R1 is the group on the benzene ring of aromatic carboxylate), L = pyridine, CH3CN, DMF, have been synthesized by the ligand substitution reaction. The dissociation of the loosely‐coordinated ligand L from the cluster core was studied by 31P NMR. The dissociation process of L is related to the solvent, temperature, and acidity of carboxylate groups, so as to affect the solution structure and reactive properties of the cluster. The long‐distance interaction between ligands RCO2 and L is transported by Mo3S4 core.

Synthesis and structural characterization of hybrid Group 12, 14, 15 metals–molybdenum (tungsten) cluster compounds

For the heterometallic cluster compounds containing a core of [M 3YS 3M′] (4+ n)+ (M=Mo, W; Y=O, S; M′=metal atom except Mo, W), a relatively comprehensive understanding has already been made when M′ n+ appears to be a transition metal. When M′ n+ is a main group metal, however, what will be the situation? This certainly arouses the interest among the chemists. In this present work, the synthesis, new reaction types, crystal structures and spectroscopic characterization of a series of 33 hybrid Mo(W)–Group 12, 14, 15 metal clusters are summarized. These crystals can be put into three categories, i.e. the single cubane type which contains a [M 3YS 3M′] core (M=Mo, W; Y=O, S; M′=Sn, Pb, Sb, Bi) (SC type), the double cubane clusters coupled by two bridging oxygen atoms possessing a [Mo 3OS 3M′ (μ-O)] 2 core (M′=Pb, Bi) (DC type) and the ionic clusters (IO type) which consists of a {Mo 3} cluster cation and a M′ complex anion (M′=Cd, Hg). It is shown that the incorporation of the main group metal M′ is through M′S bonding between M′ and three (μ-S) atoms of the [M 3YS 3] cluster core, similar to the case when M′ is a transition metal atom. The bonding is however comparatively looser than in the case of a transition metal. The synthetic reactions and structural features of these clusters are discussed. Furthermore, information on the third-order nonlinear optical property observed in some of these compounds is reported.

Dimerization of Incomplete Cuboidal Mo3S4 Units via α,ω-Dicarboxylates, and Their Supramolecular Architectures through Intermolecular S···S and C–H···S Interactions

Abstract Two novel hexanuclear molybdenum cluster compounds [Mo3S4(dtp)3(L)]2[η2-μ-OOC(CH2)nCOO-μ-η2] (n = 4, L = DMF for 1; n = 3, L = DMSO for 2) have been synthesized by reaction of Mo3S4(dtp)3(ClCH2COO)(Py) with α,ω-dicarboxylates. Intermolecular S···S and C–H···S interactions are observed, yielding two different two-dimensional supramolecular structures.

Rb2n(Mo9S11)(Mo6nS6n+2) (n=1 to 4): A Novel Family of Superconducting Molybdenum Cluster Compounds

Reinvestigation of the Rb–Mo–S system has led to the discovery of a novel family of reduced molybdenum sulfides with the general formula Rb2n(Mo9S11)(Mo6nS6n+2) (n=1 to 4) in addition to the previously known compound Rb2Mo6S6. The new rubidium-reduced molybdenum sulfides have been prepared by solid-state reaction of Rb2MoS4, MoS2, and Mo heated at temperatures ranging between 1600 K and 2000 K in a sealed Mo crucible. All members of the family crystallize in the R-3c space group with Z=6 in the hexagonal setting. X-ray diffraction studies on single crystals showed that their crystal structures consist of an equal mixture of Mo9S11 and Mo6nS6n+2 (n=1 to 4) cluster units interconnected through Mo–S bonds. The Rb+ cations occupy large voids between the different cluster units. When n goes from 1 to 4, the a parameter of the hexagonal unit cell decreases from 9.433(1) Å to 9.237(1) Å, whereas the c parameter increases linearly from 56.27(1) Å to 137.28(2) Å. Extended Hückel (tight-binding) calculations revealed that the clusters are hypoelectronic and the Fermi level crosses a rather flat band for all members of the family. Resistivity measurements carried out on single crystals from 290 K to 2 K confirmed the metallic behavior and each member was found to be a superconductor with transition temperatures ranging from 4.2 K to 10.9 K.

Synthesis and crystal structures of two new trinuclear molybdenum cluster compounds containing a [Mo 3Te 7] 4 fragment

The reaction of Kdtp (dtp=S 2P(OC 2H 5) 2, S 2P(OCH(CH 3) 2) 2) with a mixed product, prepared from the solid state reaction of molybdenum, tellurium and iodine, produces two trinuclear molybdenum cluster compounds, [Mo 3Te 7 (S 2P(OEt 2) 3]I (1) and [Mo 3Te 7 (S 2P(iPrO) 2) 3]I (2). X-ray crystal structures of 1 and 2 reveal that both compounds containing a [Mo 3Te 7] 4 core belong to the [Mo 3 ( μ 3-E) ( μ-E 2) 3] 4 (E=S, Se, Te) family and each Mo atom is further chelated by a terminated dtp − ligand. The rather strong interactions between the I and Te atoms lead to the formation of quasi-one-dimensional chains in the crystal.

X-ray crystal structures of Mo 3S 4(DTP) 3(salicylate)(CH 3CN) and [Mo 3S 4(DTP) 3(phthalate)(Py)] 2 · EtOH · CH 2Cl 2: intramolecular H-bonds and S–S interactions in trinuclear molybdenum cluster compounds

Two new molybdenum cluster compounds, Mo 3S 4(DTP) 3(salicylate)(CH 3CN) and [Mo 3S 4(DTP) 3 (phthalate)(Py)] 2 · EtOH · CH 2Cl 2, have been rationally synthesized by the ligand substitutional reaction of Mo 3S 4(DTP) 4(H 2O) with salicylic acid and phthalic acid, respectively. Their crystal structures have been determined. A molecular-design method for Mo 3S 4 cluster compounds was developed. Two incomplete cuboidal molybdenum cluster units can be linked by intramolecular H-bonds.