Exploring the Frontiers of Heterometallic Systems: the {FeW5} Octahedral Cluster Complex.

This research presents the first examples of heterometallic octahedral cluster complexes incorporating both 5d and 3d metals, specifically, tungsten and iron. The key compound, (TBA)2[FeW5Br14] (TBA = tetrabutylammonium), exhibits selective ligand substitution reactions at the iron site when exposed to various solvents. Several {FeW5}-type anions, namely, [FeW5Br14]2-, [FeW5Br13(L)]- (L = H2O, DMSO, CH3CN), and [(FeW5Br13)2O]4-, were revealed and characterized by single-crystal X-ray diffraction analysis. The redox properties of [FeW5Br14]2- were studied and compared with those of [W6Br14]2-. Density functional theory calculations demonstrated that the bonding between Fe and W atoms is fundamentally different from the bonding between 4d (Mo-Mo) or 5d (W-W) metals in isotypic {M6} clusters.

Improved Synthesis of (TBA)2[W6Br14] Paving the Way to Further Study of Bromide Cluster Complexes.

Octahedral cluster complexes of molybdenum and tungsten, [M6X8Y6]n- (M = Mo, W; X, Y = Cl, Br, I), are promising active components in various fields, including biomedicine and solar energy. Cluster complexes draw considerable attention due to their X-ray opacity, red/near-IR luminescence, and ability to convert triplet molecular oxygen to active singlet oxygen under UV and visible irradiation. Among the octahedral cluster complexes of molybdenum and tungsten, compounds with a {W6Br8}4+ core are the least studied. There are only a few examples of compounds with substituted terminal ligands, and their properties are not well understood. Among other things, this is due to more labor-intensive and expensive methods for obtaining the starting compounds in comparison with molybdenum counterparts. In this paper, we describe the synthesis of an octahedral cluster complex, (TBA)2[W6Br14] (TBA+ = tetrabutylammonium), in gram quantities, starting from simple substances─W, Br2, and Bi─in 70% yield. The formation of pentanuclear tungsten cluster complexes was recorded as a byproduct. Compounds with substituted terminal ligands (TBA)2[W6Br8Y6] (Y = NO3, Cl, I) were obtained. We also discuss the instability of (TBA)2[W6Br8(NO3)6] under light exposure, the optical properties of a series of compounds (TBA)2[W6Br8Y6] (Y = Cl, Br, I), and the effect of terminal ligands on the chemical shifts in 183W NMR spectra in dimethyl sulfoxide-d6. The presented approach to the synthesis of one of the main precursors of various bromide cluster complexes on a gram scale can stimulate the study of their properties and development of new functional materials based on them.

Unusual Square Pyramidal Chalcogenide Mo5 Cluster with Bridging Pyrazolate-Ligands.

The family of chalcogenide molybdenum clusters is well presented in the literature by a series of compounds of nuclearity ranging from binuclear to multinuclear articulating octahedral fragments. Clusters actively studied in the last decades were shown to be promising as components of superconducting, magnetic, and catalytic systems. Here, we report the synthesis and detailed characterization of new and unusual representatives of chalcogenide clusters: square pyramidal complexes [{Mo5(µ3-Se)i4(µ4-Se)i(µ-pz)i4}(pzH)t5]1+/2+ (pzH = pyrazole, i = inner, t = terminal). Individually obtained oxidized (2+) and reduced (1+) forms have very close geometry (proven by single-crystal X-ray diffraction analysis) and are able to reversibly transform into each other, which was confirmed by cyclic voltammetry. Comprehensive characterization of the complexes, both in solid and in solution, confirms the different charge state of molybdenum in clusters (XPS), magnetic properties (EPR), and so on. DFT calculations complement the diverse study of new complexes, expanding the chemistry of molybdenum chalcogenide clusters.

Water-Soluble Polyoxometal Clusters of Molybdenum (V) with Pyrazole and Triazole: Synthesis and Study of Cytotoxicity and Antiviral Activity.

Among well-studied and actively developing compounds are polyoxometalates (POMs), which show application in many fields. Extending this class of compounds, we introduce a new subclass of polyoxometal clusters (POMCs) [Mo12O28(µ-L)8]4- (L = pyrazolate (pz) or triazolate (1,2,3-trz or 1,2,4-trz)), structurally similar to POM, but containing binuclear Mo2O4 clusters linked by bridging oxo- and organic ligands. The complexes obtained by ampoule synthesis from the binuclear cluster [Mo2O4(C2O4)2(H2O)2]2- in a melt of an organic ligand are soluble and stable in aqueous solutions. In addition to the detailed characterization in solid state and in aqueous solution, the biological properties of the compounds on normal and cancer cells were investigated, and antiviral activity against influenza A virus (subtype H5N1) was demonstrated.

Stabilization of Octahedral Metal Halide Clusters by Host-Guest Complexation with γ-Cyclodextrin: Toward Nontoxic Luminescent Compounds.

γ-Cyclodextrin (γ-CD) interacts in aqueous solution with octahedral halide clusters Na2[{M6X8}Cl6] (M = Mo, W; X = Br, I) to form robust inclusion supramolecular complexes [{M6X8}Cl6@2γ-CD]2-. Single-crystal X-ray diffraction analyses revealed two conformational organizations within the adduct depending on the nature of the inner halide X within the {M6X8} core. Using 35Cl NMR and UV-vis as complementary techniques, the kinetics of the hydrolysis process were shown to increase with the following order: {W6I8} < {W6Br8} ≈ {Mo6I8} < {Mo6Br8}. The complexation with γ-CD drastically enhances the hydrolytic stability of luminescent [{M6X8}Cl6]2- cluster-based units, which was quantitatively proved by the same techniques. The resulting host-guest complexation provides a protective shell against contact with water and offers promising horizons for octahedral clusters in biology as revealed by the low dark cytotoxicity and cellular uptake.

From Photoinduced to Dark Cytotoxicity through an Octahedral Cluster Hydrolysis.

Octahedral molybdenum and tungsten clusters have potential biological applications in photodynamic therapy and bioimaging. However, poor solubility and hydrolysis stability of these compounds hinder their application. The first water-soluble photoluminescent octahedral tungsten cluster [{W6 I8 }(DMSO)6 ](NO3 )4 was synthesised and demonstrated to be at least one order of magnitude more stable towards hydrolysis than its molybdenum analogue. Biological studies of the compound on larynx carcinoma cells suggest that it has a significant photoinduced toxicity, while the dark toxicity increases with the increase of the degree of hydrolysis. The increase of the dark toxicity is associated with the in situ generation of nanoparticles that clog up the cisternae of rough endoplasmic reticulum.

Octahedral molybdenum cluster as a photoactive antimicrobial additive to a fluoroplastic.

Finding methods that fight bacterial infection or contamination, while minimising our reliance on antibiotics is one of the most pressing needs of this century. Although the utilisation of UV-C light and strong oxidising agents, such as bleach, are still efficacious methods for eliminating bacterial surface contamination, both methods present severe health and/or environmental hazards. Materials with intrinsic photodynamic activity (i.e. a material's ability upon photoexcitation to convert molecular oxygen into reactive oxygen species such as singlet oxygen), which work with light within the visible photomagnetic spectrum could offer a significantly safer alternative. Here we present a new, bespoke molybdenum cluster (Bu4N)2[{Mo6I8}(CF3(CF2)6COO)6], which is both efficient in the generation of singlet oxygen upon photoirradiation and compatible with the fluoropolymer (F-32L) known for its good oxygen permeability. Thus, (Bu4N)2[{Mo6I8}(CF3(CF2)6COO)6]/F-32L mixtures have been solution-processed to give homogenous films of smooth and fibrous morphologies and which displayed high photoinduced antibacterial activity against four common pathogens under visible light irradiation. These materials thus have potential in applications ranging from antibacterial coatings to filtration membranes and air conditioners to prevent spread of bacterial infections.

A comparative study of optical properties and X-ray induced luminescence of octahedral molybdenum and tungsten cluster complexes.

Octahedral metal cluster complexes have high potential for biomedical applications. In order to evaluate the benefits of these moieties for combined CT/X-ray luminescence computed tomography, this paper compares photoluminescence, radiodensity and X-ray induced luminescence properties of eight related octahedral molybdenum and tungsten cluster complexes [{M6I8}L6]n (where M is Mo or W and L is I-, NO3-, OTs- or OH-/H2O). This article demonstrates that despite the fact that molybdenum cluster complexes are better photoluminescence emitters, tungsten cluster complexes, in particular (Bu4N)2[{W6I8}I6], demonstrate significantly higher X-ray induced luminescence due to a combination of relatively good photoluminescence properties and high X-ray attenuation. Additionally, photo-degradation of [{M6I8}(NO3)6]2- was evaluated.