The redox-active rhenium octahedral cluster unit Re6Se8(CN)64– was combined with Gd3+ ions and dicarboxylate linkers in novel types of metal–organic frameworks (MOFs) that display a set of functional ...properties. The hydrolytically stable complexes {Gd(H2O)3}2(L)Re6Se8(CN)6·nH2O (1, L = furan-2,5-dicarboxylate, fdc; 2, L = thiophene-2,5-dicarboxylate, tdc) exhibit a 3D framework of trigonal symmetry where 1D chains of {Gd(H2O)3}2(L)4+ are connected by Re6Se8(CN)64– clusters. Frameworks contain spacious channels filled with H2O. Solvent molecules can be easily removed under vacuum to produce permanently porous solids with high volumetric CO2 uptake and remarkable CO2/N2 selectivity at room temperature. The frameworks demonstrate an ability for reversible redox transformations of the cluster fragment. The orange powders of compounds 1 and 2 react with Br2, yielding dark-green powders of {Gd(H2O)3}2(L)Re6Se8(CN)6Br·nH2O (3, L = fdc; 4, L = tdc). Compounds 3 and 4 are isostructural with 1 and 2 and also have permanently porous frameworks but display different optical, magnetic, and sorption properties. In particular, oxidation of the cluster fragment “switches off” its luminescence in the red region, and the incorporation of Br– leads to a decrease of the solvent-accessible volume in the channels of 3 and 4. Finally, the green powders of 3 and 4 can be reduced back to the orange powders of 1 and 2 by reaction with hydrazine, thus displaying a rare ability for fully reversible chemical redox transitions. Compounds 1–4 are mentioned as a new class of redox-active cluster-based MOFs with potential usage as multifunctional materials for gas separation and chemical contamination sensors.
Inclusion compounds of photoluminescent hexamolybdenum cluster complexes in the chromium terephthalate metal-organic framework, MIL-101 (MIL, Matérial Institut Lavoisier) were successfully ...synthesized in two different ways and characterized by means of powder X-Ray diffraction, chemical analysis and nitrogen sorption. Some important functional properties of hexamolybdenum cluster complexes for biological and medical applications, in particular singlet oxygen generation ability, luminescence properties, cellular uptake behavior and cytotoxicity were studied. It was revealed that the inclusion compounds possessed significant singlet oxygen generation activity. The materials obtained showed a low cytotoxicity, thus allowing them to be used in living cells. Confocal microscopy of human larynx carcinoma (Hep-2) cells incubated with the inclusion compounds showed that MIL-101 performed as a nanocarrier adhering to the external cell membrane surface and releasing the cluster complexes which that penetrated into the cells. Moreover, photoinduced generation of reactive oxygen species (ROS) in Hep-2 cells incubated with inclusion compounds was demonstrated. The cluster supported on MIL-101 was shown to possess in vivo phototoxicity.
Hexamolybdenum clusters possessing red fluorescence were introduced into nanosized chromium terephthalate metal-organic framework. Clusters anchored via pyrazine cannot penetrate into cells whereas clusters from pyrazine-free compound transport through membrane and generate singlet oxygen in cancer Hep-2 cells. Thus, such system is a suitable nanocarrier for applications in photodynamic therapy. Display omitted
•Molybdenum clusters in mesoporous chromium terephthalate metal-organic framework.•Luminescence of hybrids were investigated and compared to clusters in solutions.•Cytotoxicity of all compounds were established at low level.•Penetration of clusters into Hep-2 cells were observed for pyrazine-free compound.•Generation of reactive oxygen species were tested in vitro and in living cells.
A series of eight new octahedral rhenium cluster complexes with the general formula
-{Re
Q
}L
X
(Q = S or Se; L = 1,2-Bis(4-pyridyl)ethylene (bpe) or 1,3-Bis(4-pyridyl)propane (bpp); X = Cl or Br) ...was synthesized and investigated. While bpe is a ligand with a conjugated aromatic system, bpp represents a molecule of opposite type and has independent aromatic systems of the two pyridine rings. It was shown that this difference in the electronic structure of the ligands has a fundamental effect on the electronic structure, electrochemical and luminescent properties of the corresponding cluster complexes. Specifically, the {Re
Q
}(bpe)
X
complexes in solutions show multiple quasi-reversible electrochemical transitions associated with reduction of the organic ligands. At the same time, the
-{Re
Q
}(bpp)
X
complexes show multielectron quasi-irreversible reduction processes, which correlate with the mixed character of the lowest unoccupied molecular orbitals of these complexes. All the obtained new compounds exhibit red photoluminescence. The photophysical parameters (emission lifetimes and quantum yields) measured for the bpp complexes exceed those revealed for bpe complexes by more than an order of magnitude.
The association of metallic clusters (CLUS) and polyoxometalates (POM) into hierarchical architectures is achieved using γ-cyclodextrin (γ-CD) as a supramolecular connector. The new self-assembled ...systems, so-called CLUSPOM, are formed from Dawson-type polyoxometalate P2W18O626– and electron-rich rhenium clusters. It is worth noting that a cluster-based cation {Re6Se8}(H2O)62+ on one hand and a cluster-based anion on the other hand {Re6Se8}(CN)64– can be associated with the anionic POM. In the absence of the supramolecular connector, a “CLUSPOM salt” was obtained from aqueous solution of the cationic cluster and the polyoxometalate. In this solid, the arrangement between the polymetallic building blocks is mainly governed by long-range Coulombic interactions. In the presence of γ-CD, the Dawson anion and the cationic cluster are assembled differently, forming a hierarchical supramolecular solid, K2{Re6Se8}(H2O)62{P2W18O62@2γ-CD}·42H2O, where the organic macrocycle acts as a ditopic linker between the inorganic building blocks. In such an edifice, the short-range molecular recognition dominates the long-range Coulombic interactions leading to a specific three-dimensional organization. Interestingly, the assembling of anionic POM P2W18O626– with the anionic rhenium cluster {Re6Se8}(CN)64– is also achieved with γ-CD despite the repulsive forces between the nanosized anions. The resulting solid, K10{{Re6Se8}(CN)6@2γ-CD}P2W18O62·33H2O, is built from 1:2 inclusion complexes {{Re6Se8}(CN)6@2γ-CD}4– linked by a POM unit interacting with the exterior wall of the organic macrocycle. Multinuclear NMR and small-angle X-ray scattering investigations support supramolecular preorganization in aqueous solution prior to crystallization.
A series of six coordination polymers based on octahedral cluster anions Re
Q
(CN)
(Q = S or Se) and Ag
cations coordinated by bipyridine analogs were synthesized under solvothermal conditions. ...Their structures have been characterized by single crystal X-ray diffraction. Compounds
and
described by the general formula {Ag(phen)}
Re
Q
(CN)
(Q = Se (
), S (
); phen = 1,10-phenanthroline) exhibit layered structures assembled into a supramolecular network by CH…π contacts. At the same time, compounds {Ag(bipym)}
Ag
Re
Se
(CN)
(bipym = 2,2'-bipyrimidine) (
), {Ag
(bipy)}Ag
Re
Se
(CN)
·CH
CN (bipy = 4,4'-bipyridine) (
) and {Ag(dpbp)}
Re
Q
(CN)
·2H
O·2CH
CN (Q = Se (
), S (
); dpbp = 4,4'-Di(4-pyridyl)biphenyl)) evince framework structures. In
,
,
and
weak Ag⋯Ag interactions are observed. All the compounds show luminescence in the red region. The luminescence quantum yields and lifetimes were found to be notably higher than those for most of the coordination polymers based on the octahedral rhenium cluster complexes.
Investigation of new X-ray contrast media for radiography is an important field of science since discovering of X-rays in 1895. Despite the wide diversity of available X-ray contrast media the ...toxicity, especially nephrotoxicity, is still a big problem to be solved. The octahedral metal-cluster complexes of the general formula {M6Q8}L6 can be considered as quite promising candidates for the role of new radiocontrast media due to the high local concentration of heavy elements, high tuning ability of ligand environment and low toxicity. To exemplify this, the X-ray computed tomography experiments for the first time were carried out on some octahedral cluster complexes of molybdenum and rhenium. Based on the obtained data it was proposed to investigate the toxicological proprieties of cluster complex Na2H8{Re6Se8}(P(CH2CH2CONH2)(CH2CH2COO)2)6. Observed low cytotoxic and acute toxic effects along with rapid renal excretion of the cluster complex evidence its perspective as an X-ray contrast media for radiography.
The applicability of the hexanuclear metal cluster complexes as agents for X-ray contrast media was demonstrated. The highly radiopaque cluster cores {M6Q8} along with high tuning ability of the outer ligand environment allow creating a complex with low toxicity and rapid renal excretion. Display omitted
•The radiopacity of different cluster compounds was shown.•The applicability of the clusters as agents for X-ray contrast media was demonstrated.•Complex 8 excretes through the kidneys rapidly.
The development of novel radiocontrast agents, mainly used for the visualization of blood vessels, is still an emerging task due to the variety of side effects of conventional X-ray contrast media. ...Recently, we have shown that octahedral chalcogenide rhenium clusters with phosphine ligands—Na2H14{Re6Q8}(P(C2H4COO)3)6 (Q = S, Se)—can be considered as promising X-ray contrast agents if their relatively high toxicity related to the high charge of the complexes can be overcome. To address this issue, we propose one of the most widely used methods for tuning the properties of proteins and peptides—PEGylation (PEG is polyethylene glycol). The reaction between the clusters and PEG-400 was carried out in acidic aqueous media and resulted in the binding of up to five carboxylate groups with PEG. The study of cytotoxicity against Hep-2 cells and acute toxicity in mice showed a twofold reduction in toxicity after PEGylation, demonstrating the success of the strategy chosen. Finally, the compound obtained has been used for the visualization of blood vessels of laboratory rats by angiography and computed tomography.
The embedding of functional inorganic entities into polymer matrices has become an intense field of investigation in which the main challenges are to keep the added value of the inorganic entities ...while preventing their self‐aggregation within the organic matrix. We present a simple way to obtain a homogeneous highly red‐NIR luminescent hybrid copolymer that contains covalently bonded nanometric‐sized {Re6} octahedral clusters. The Re6Sei8(OH)a64− cluster complexes are primarily functionalized in two steps with tert‐butylpyridine (TBP) and methacrylic acid (MAC) to give neutral Re6Se8(TBP)4(MAC)2 building blocks that are copolymerized with methyl methacrylate (MMA) either in solution or in bulk in the presence of azobisisobutyronitrile as an initiator. Several samples containing 0, 0.025, 0.05, and 0.1 wt % of functionalized {Re6} clusters were prepared. As the {Re6} cluster/MMA ratio is very low, the obtained copolymers keep the entire processability of pure poly(methyl methacrylate) (PMMA), as demonstrated by differential scanning calorimetry and thermogravimetric analysis. Voltammetric and luminescence studies also indicate that the intrinsic properties of the clusters are preserved within the polymer matrix. All the samples show a bright (emission quantum yield=0.07), broad, and structureless emission band, which extends from λ=600 nm to more than λ=950 nm, with the maximum wavelength centered around λem=710 nm either in solution or in the solid state. Moreover, the high stability of the incorporated inorganic phosphors prevents the material from photobleaching, and thus the luminescence properties are kept entirely even after nine months of ageing.
Shining in red: Functionalized octahedral {Re6} clusters were copolymerized with methyl methacrylate to give photoluminescent hybrid materials. Both the processability of the homopolymer and the photoluminescence properties in the red‐NIR region of the inorganic cluster core are preserved in these hybrid materials with quantum yields of luminescence equal to 0.07 (see picture).
In aqueous solution, cyclodextrins (CDs) are able to bind strongly either hydrophobic species or also hydrophilic molecules such as octahedral hexametallic cluster. Systematic investigation of the ...reactivity between native CDs (α- or β-CD) and water-soluble rhenium clusters Re6Q8(CN)64– with Q = S, Se, and Te were performed, leading to six new crystal structures revealing different types of supramolecular arrangements. Encapsulation of Re6Q8(CN)64– (Q = S, Se, or Te) within two β-CDs is observed regardless of the cluster size. Interestingly, different assembling scenarios are pointed out depending on the host–guest matching featured by no, partial, or deep inclusion complexes that involved either primary or secondary rim of the CD tori. In the specific case of α-CD, only the smaller cluster Re6S8(CN)64– is able to form inclusion complex with the tori host. Solution investigations, using a set of complementary techniques including isothermal titration calorimetry, multinuclear NMR methods, cyclic voltammetry, and electrospray ionization mass spectrometry, corroborate nicely conclusions of the solid-state studies. It appears clearly that size-matching supported by solvent effects play key roles in the stability of the host–guest complexes. At last, circular dichroism studies underline that the chirality induction from cyclodextrins to the rhenium cluster depends strongly on the strength of host–guest interactions.
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