Supramolecular hybrids based on Ru(II) porphyrin and octahedral Mo(II) iodide cluster.

The coordination-driven design and synthesis of new stable supramolecular cluster-porphyrin (CP) hybrids based on an A2-type ruthenium porphyrin 5,15-bis[(p-tolyl)porphyrinato(2-)]ruthenium(carbonyl)(aqua) [RuDTolP(CO)H2O] and an octahedral molybdenum(II) iodide cluster with six terminal isonicotinate ligands (Bu4N)2[{Mo6I8}(OOC-C5H4N)6] (PyMoC) are reported. The stepwise supramolecular assembly of the PyMoC "superoctahedron" with RuDTolP(CO)H2O has been studied by 1H NMR and 2D 1H-1H COSY, 1H-15N HMBC and DOSY techniques, as well as by UV-vis spectroscopy and HR-ESI mass spectrometry. The formation of discrete cluster-porphyrin CPn adducts with different numbers of coordinated porphyrins (n = 1-6), including the geometrical isomers of CP2, CP3 and CP4, has been observed. Using a double equivalent amount of RuDTolP(CO)H2O relative to the cluster (C : P ratio 1 : 12) affords a mixture of CP5 and CP6 species in solution, while only the CP6 complex is crystallized from this system. Fine tuning of crystallization conditions leads to the formation of a more complex architecture CP6+2, where the CP6 assembly incorporates two additional porphyrin molecules bound to the cluster core by hydrogen bonds. Thus, the coordination-based supramolecular approach provides new stable cluster-multiporphyrin 3D arrays based on two types of photosensitizers, which can be promising for the design of photoactive materials.

Enhancement of photoactivity and cellular uptake of (Bu4N)2[Mo6I8(CH3COO)6] complex by loading on porous MCM-41 support. Photodynamic studies as an anticancer agent.

The incorporation by ionic assembly of the hexanuclear molybdenum cluster (Bu4N)2[Mo6I8(CH3CO2)6] (1) in amino-decorated mesoporous silica nanoparticles MCM-41, has yielded the new molybdenum-based hybrid photosensitizer 1@MCM-41. The new photoactive material presents a high porosity, due to the intrinsic high specific surface area of MCM-41 nanoparticles (989 m2 g-1) which is responsible for the good dispersion of the hexamolybdenum clusters on the nanoparticles surface, as observed by STEM analysis. The hybrid photosensitizer can generate efficiently singlet oxygen, which was demonstrated by using the benchmark photooxygenation reaction of 9,10-anthracenediyl-bis(methylene)dimalonic acid (ABDA) in water. The photodynamic therapy activity has been tested using LED light as an irradiation source (λirr ~ 400-700 nm; 15.6 mW/cm2). The results show a good activity of the hybrid photosensitizer against human cervical cancer (HeLa) cells, reducing up to 70 % their viability after 20 min of irradiation, whereas low cytotoxicity is detected in the darkness. The main finding of this research is that the incorporation of molybdenum complexes at porous MCM-41 supports enhances their photoactivity and improves cellular uptake, compared to free clusters.

Paramagnetic Rhenium Iodide Cluster with N-Heterocyclic Carbene.

triangulo-Trirhenium nonaiodide Re3I9 reacts with 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) to produce the novel 13-electron paramagnetic cluster Re3I8(IMes)2, which was characterized by means of X-ray diffraction analysis, ESR spectroscopy, magnetometry, and quantum chemistry.

Photodynamic Inactivation of Staphylococcus aureus Biofilms Using a Hexanuclear Molybdenum Complex Embedded in Transparent polyHEMA Hydrogels.

Three new photoactive polymeric materials embedding a hexanuclear molybdenum cluster (Bu4N)2[Mo6I8(CH3COO)6] (1) have been synthesized and characterized by means of Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and emission spectroscopy. The materials are obtained in the format of transparent and thin sheets, and the formulations used to synthesize them are comprised of 2-hydroxyethyl methacrylate (HEMA), as a polymerizable monomer, and ethylene glycol dimethacrylate (EGDMA) or poly(ethylene glycol)dimethacrylate (PEGDMA), as cross-linkers. All the polymeric hydrogels generate singlet oxygen (1O2) upon irradiation with visible light (400-700 nm), as demonstrated by the reactivity toward two chemical traps of this reactive species (9,10-dimethylanthracene and 1,5-dihydroxynaphthalene). Some differences have been detected between the photoactive materials, probably attributable to variations in the permeability to solvent and oxygen. Notably, one of the materials resisted up to 10 cycles of photocatalytic oxygenation reactions of 1,5-dihydroxynaphthalene. All three of the polyHEMA hydrogels doped with 1 are efficient against S. aureus biofilms when irradiated with blue light (460 nm). The material made with the composition of 90% HEMA and 10% PEGDMA (Mo6@polymer-III) is especially easy to handle, because of its flexibility, and it achieves a notable level of bacterial population reduction (3.0 log10 CFU/cm2). The embedding of 1 in cross-linked polyHEMA sheets affords a protective environment to the photosensitizer against aqueous degradation while preserving the photochemical and photobactericidal activity.

Enhanced Photocatalytic Activity and Stability in Hydrogen Evolution of Mo6 Iodide Clusters Supported on Graphene Oxide.

Catalytic properties of the cluster compound (TBA)2[Mo6Ii8(O2CCH3)a6] (TBA = tetrabutylammonium) and a new hybrid material (TBA)2Mo6Ii8@GO (GO = graphene oxide) in water photoreduction into molecular hydrogen were investigated. New hybrid material (TBA)2Mo6Ii8@GO was prepared by coordinative immobilization of the (TBA)2[Mo6Ii8(O2CCH3)a6] onto GO sheets and characterized by spectroscopic, analytical, and morphological techniques. Liquid and, for the first time, gas phase conditions were chosen for catalytic experiments under UV-Vis irradiation. In liquid water, optimal H2 production yields were obtained after using (TBA)2[Mo6Ii8(O2CCH3)a6] and (TBA)2Mo6Ii8@GO) catalysts after 5 h of irradiation of liquid water. Despite these remarkable catalytic performances, "liquid-phase" catalytic systems have serious drawbacks: the cluster anion evolves to less active cluster species with partial hydrolytic decomposition, and the nanocomposite completely decays in the process. Vapor water photoreduction showed lower catalytic performance but offers more advantages in terms of cluster stability, even after longer radiation exposure times and recyclability of both catalysts. The turnover frequency (TOF) of (TBA)2Mo6Ii8@GO is three times higher than that of the microcrystalline (TBA)2[Mo6Ii8(O2CCH3)a6], in agreement with the better accessibility of catalytic cluster sites for water molecules in the gas phase. This bodes well for the possibility of creating {Mo6I8}4+-based materials as catalysts in hydrogen production technology from water vapor.

Octahedral {Ta6I12} Clusters.

Ta powder reacts with I2 at 650 °C with the formation of Ta6I14, which belongs to the family of {M6(µ-X)12} clusters. It undergoes aquation with the formation of the intensely colored [Ta6I12(H2O)6]2+. The crystal structure was determined for [Ta6I12(H2O)6](BPh4)2·xH2O (Ta-Ta 2.9322(6) Å, Ta-I 2.8104(7) Å, Ta-O 2.3430(5) Å). With DMF, [Ta6I12(DMF)6]I2·xDMF was isolated (Ta-Ta 2.9500(2) Å, Ta-I 2.8310(4) Å, Ta-O 2.2880(7) Å). Cyclic voltammetry of [Ta6I12(H2O)6]2+ shows two consecutive quasi-reversible one-electron oxidations (E1/2 0.61 and 0.92 V vs Ag/AgCl). Reaction of Ta6I14 with Bu4NCN yields (Bu4N)4[Ta6I12(CN)6]·xCH3CN (Ta-Ta 2.9777(4) Å, Ta-I 2.8165(6) Å, Ta-C 2.2730(7) Å). Quantum chemical calculations reproduce well the experimental geometry of the aqua complex and show the essentially Ta-centered nature of both the HOMO and LUMO. The long-term stability of [Ta6I12(H2O)6]2+ solutions can be greatly enhanced in the presence of polystyrenesulfonate (PSS), which forms nanoparticle associates with the aqua complex in water (ca. 1 cluster per 3 PSS monomeric units).

Hybrid organic-inorganic supramolecular systems based on a pyridine end-decorated molybdenum(ii) halide cluster and zinc(ii) porphyrinate.

Herein, first examples of supramolecular hybrid organic-inorganic cluster-porphyrin [CPn (n = 2, 6)] systems constructed via metal-ligand coordination have been reported. The pyridine end-decorated Mo(ii) halide cluster ((Bu4N)2[{Mo6I8}(OOC-C5H4N)6]), possessing remarkable photophysical properties, was chosen as the inorganic part and A2-type zinc porphyrin 5,15-bis[(p-tolyl)porphyrinato(2-)]zinc was selected as the organic part. The crystal structures of CP2 and CP6 hybrids have been characterised by single crystal X-ray diffraction. The CP2 complex is composed of two zinc porphyrins, coordinated to pyridyl moieties of the same cluster molecule, related by an inversion center. In the case of the CP6 complex, each cluster has three pairs of coordinated symmetrically equivalent zinc porphyrins. Also, the formation of supramolecular hybrid CPn (n = 2, 6) systems was unambiguously demonstrated in solution via NMR and UV-Vis spectroscopy titration and diffusion ordered NMR spectroscopy (DOSY).