Octahedral Rhenium Cluster Complexes Research Articles

Octahedral Rhenium Cluster Complexes with 1,2-Bis(4-pyridyl)ethylene and 1,3-Bis(4-pyridyl)propane as Apical Ligands.

A series of eight new octahedral rhenium cluster complexes with the general formula trans-[{Re6Q8}L4X2] (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 [{Re6Q8}(bpe)4X2] complexes in solutions show multiple quasi-reversible electrochemical transitions associated with reduction of the organic ligands. At the same time, the trans-[{Re6Q8}(bpp)4X2] 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.

Coordination Polymers Based on Rhenium Octahedral Chalcocyanide Cluster Anions and Ag+ Cations with Bipyridine Analogs.

A series of six coordination polymers based on octahedral cluster anions [Re6Q8(CN)6]4- (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 1 and 2 described by the general formula [{Ag(phen)}4Re6Q8(CN)6] (Q = Se (1), S (2); phen = 1,10-phenanthroline) exhibit layered structures assembled into a supramolecular network by CH…π contacts. At the same time, compounds [{Ag(bipym)}2Ag2Re6Se8(CN)6] (bipym = 2,2'-bipyrimidine) (3), [{Ag2(bipy)}Ag2Re6Se8(CN)6]·CH3CN (bipy = 4,4'-bipyridine) (4) and [{Ag(dpbp)}4Re6Q8(CN)6]·2H2O·2CH3CN (Q = Se (5), S (6); dpbp = 4,4'-Di(4-pyridyl)biphenyl)) evince framework structures. In 1, 2, 5 and 6 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.

CRYSTAL STRUCTURE AND LUMINESCENT PROPERTIES OF RHENIUM CLUSTERS [{Re6(μ3-Q)8}(imz-[1,2-a]py)6]Br2

Octahedral rhenium cluster complexes of the composition [{Re6(μ3-Q)8}(imz-[1,2-a]py)6]Br2, where Q = S, Se, are obtained by the interaction of Csn[{Re6(μ3-Q8)}Br6] (n = 4 for Q = S; n = 3 for Q = Se) with an excess of imidazo-[1,2-а]pyridine in a sealed glass ampoule at 180 °С within two days. Both compounds are isostructural and crystallize in the trigonal space group $$R\bar{3}$$ . The crystal structure of the complexes represents three differently directed chains of [{Re6Q8}(imz-[1,2-a]py)6]2+ cations and bromine anions linked with each other by С–H⋯Br⋯H–C hydrogen bonds. The compounds obtained have pronounced luminescence with emission maxima at 652 nm and 678 nm for Q = S, Se respectively.

Apically homoleptic octahedral rhenium cluster complexes with 3-methylpyrazole

Octahedral rhenium cluster complexes with organic apical ligands have a high potential to be used in different fields due to their intrinsic luminescence and X-ray contrast properties. A series of new compounds based on cations [{Re6Q8}(3-Me-pzH)6]2+, where Q is S or Se and 3-Me-pzH is 3-methylpyrazole, were obtained and characterized in the solid state (FTIR, elemental and single crystal diffraction analysis) and in solution (1H NMR and ESI-MS). The compounds possess luminescence properties that mainly depend on inner Q ligands indicating the {Re6Q8}2+ core-centered nature of emission.

Soluble Molecular Rhenium Cluster Complexes Exhibiting Multistage Terminal Ligands Reduction.

Substitution of terminal halide ligands of octahedral rhenium cluster complexes [Re6Q8X6]4- in a melt of 4,4'-bipyridine (bpy) led to us obtaining four new compounds with the general formula trans-[Re6Q8(bpy)4X2] (Q = S or Se; X = Cl or Br) in high yield. In contrast to most of the known molecular rhenium cluster complexes with heteroaromatic terminal ligands, compounds 1-4 are soluble in organic solvents. This made it possible to carry out a detailed characterization of the new compounds both in solids and in solutions. In particular, it was shown that compounds 1-4 in the DMSO solution exhibit four reversible reduction processes. A comparison of the obtained data with the results of DFT calculations of the electronic structure suggests that these processes correspond to two-electron reduction of all four bpy ligands. The reduction potentials are shifted to the positive region compared with the potential of free bipyridine, and the value of the shift depends on the composition of the cluster core. The presence of four transitions also suggests that electronic exchange between terminal ligands in the cis-position is possible. The study of the luminescence of the compounds showed that emission maxima of selenide clusters almost coincide with those of sulfide ones, while luminescence spectra of the complexes with chloride terminal ligands (1 and 3) are slightly blue-shifted relative to the spectra of the complexes with bromide ligands (2 and 4).

[{Re6Q8}(SO3)6]10- (Q = S or Se): Facile Synthesis and Properties of the Most Highly Charged Octahedral Cluster Complexes and High Magnetic Relaxivity of Their Colloids with Gd3+ Ions.

New octahedral rhenium cluster complexes [{Re6Q8}(SO3)6]10- (Q = S or Se) were synthesized starting from [{Re6Q8}(H2O)4(OH)2]·12H2O. The complexes were crystallized as sodium salts and characterized by X-ray single-crystal diffraction and elemental analyses, IR, UV/vis and luminescence spectroscopies. Magnetic relaxation data demonstrate the complex formation of the cluster units with gadolinium ions. The analysis of the magnetic relaxation rates measured at various Gd:cluster ratios and different concentrations revealed the conversion of the aggregates (Gdx[{Re6Se8}(SO3)6]y)n- into a nanoparticulate form even at x = 1 and y ≥ 1. Thus, the self-assembly of the cluster units into the nanoparticles is greatly facilitated by counterion binding with sodium cations. The concentration conditions were optimized for the formation and hydrophilization of NaxGdy[{Re6Q8}(SO3)6]-based colloids with the magnetic relaxivity values of r1(2) = 21.0(24.1) and r1(2) = 25.9(29.8) mM-1 s-1 for the {Re6S8}2+ and {Re6Se8}2+ derivatives, respectively.

Singlet Oxygen Production and Biological Activity of Hexanuclear Chalcocyanide Rhenium Cluster Complexes [{Re6Q8}(CN)6]4– (Q = S, Se, Te)

Octahedral rhenium cluster complexes have recently emerged as relevant building blocks for the design of singlet oxygen photosensitizing materials toward biological applications such as blue-light photodynamic therapy. However, their singlet oxygen generation ability as well as biological properties have been studied only superficially. Herein we investigate in detail the singlet oxygen photogeneration, dark and photoinduced cytotoxicity, cellular uptake kinetics, cellular localization and in vitro photoinduced oxidative stress, and photodynamic cytotoxicity of the series of octahedral rhenium cluster complexes [{Re6Q8}(CN)6]4-, where Q = S, Se, Te. Our results demonstrate that the selenium-containing complex possesses optimal properties in terms of absorption and singlet oxygen productivity. These features coupled with the cellular internalization and low dark toxicity lead to the first photoinduced cytotoxic effect observed for a molecular [{M6Q8}L6] complex, making it a promising object for further study in terms of blue-light PDT.

Comprehensive study of hexarhenium cluster complex Na4[{Re6Te8}(CN)6] – In terms of a new promising luminescent and X-ray contrast agent

Octahedral rhenium cluster complexes may have considerable potential as therapeutic and diagnostic drugs due to their luminescent and X-ray contrast properties, as well as their ability to generate singlet oxygen upon photoirradiation. However, their potential biological effects and toxicity in vitro and in vivo are rather far from being understood. Thus, the aim of our research was to study cytotoxicity, intracellular localization and cellular uptake/elimination kinetics in vitro, biodistribution and acute intravenous toxicity in vivo of a complex Na4[{Re6Te8}(CN)6] as the promising compound for biomedical application. The results have demonstrated that the complex penetrates through cell membranes with the maximum accumulation in cells in 24h of incubation and have low toxic effects in vitro and in vivo. The median lethal dose (LD50) of intravenously administrated Na4[{Re6Te8}(CN)6] is equal to 1082±83mg/kg. These findings will be useful for future development of cluster-based agents for different biomedical applications.

Synthesis, structure and luminescence properties of new chalcogenide octahedral rhenium cluster complexes with 4-aminopyridine [{Re6Q8}(4-NH2-py)6]2+

Two new cationic octahedral rhenium cluster complexes [{Re6Q8}(4-NH2-py)6]2+ (Q=S, Se; 4-NH2-py = 4-aminopyridine) were synthesized by reactions of cesium salts of cluster anions [{Re6Q8}Br6]4−/3− with molten 4-aminopyridine. Both complexes were separated as salts with Br− as counterions and the structure of [{Re6S8}(4-NH2-py)6]Br2·6DMF was revealed by X-ray single-crystal diffraction analysis. The compounds were characterized by elemental analysis, energy dispersive X-ray, IR, NMR, and luminescence spectroscopies.

A family of octahedral rhenium cluster complexes trans-[{Re6Q8}(PPh3)4X2] (Q = S or Se, X = Cl, Br or I): Preparation and halide-dependent luminescence properties

Four new octahedral rhenium cluster complexes trans-[{Re6Q8}(PPh3)4X2] (Q=S, Se; X=Cl, I) were synthesized by reaction of cesium salts of cluster anions [{Re6Q8}X6]4−/3− with molten triphenylphosphine. The compounds were characterized by elemental and X-ray structural analyses. Emission spectra and photophysical characteristics for all new compounds and earlier described trans-[{Re6Q8}(PPh3)4Br2] were obtained showing a dependence of the emission maximum wavelength, quantum yield and lifetime values from cluster ligand environment.

Polymerisable octahedral rhenium cluster complexes as precursors for photo/electroluminescent polymers

Re-containing cluster complexes have been developed and polymerised to generate photo/electroluminescent materials, which can be used to construct PLEDs.

ChemInform Abstract: Tellurium-Containing Rhenium Cluster Complexes

Synthetic procedures as well as the structures and some properties of tetrahedral and octahedral tellurium-containing rhenium cluster complexes are reported. Crystal chemistry of various types of structure is discussed.

Cellular uptake and cytotoxicity of octahedral rhenium cluster complexes

Cellular uptake behavior of a novel class of octahedral rhenium cluster compounds, hexahydroxo complexes K 4[{Re 6S 8}(OH) 6] · 8H 2O (1) and K 4[{Re 6Se 8}(OH) 6] · 8H 2O (2), was evaluated in human cervical adenocarcinoma HeLa cells. Confocal microscopy and flow cytometry studies demonstrated that rhenium cluster 1 was not internalized into cell, while rhenium cluster 2 was. Conjugation of a polymer to rhenium cluster 1, namely the derivative K 4[{Re 6S 8}(OH) 5 L] (3) ( L is amphiphilic diblock copolymer MPEG550-CH 2CONH–GlyPheLeuGlyPheLeu–COO −), considerably enhanced cellular uptake in a concentration-dependent manner and was predominantly localized in the cytoplasm and nucleus upon incubation time. The uptake of rhenium cluster 2 was mediated by energy-dependent endocytosis, whereas rhenium cluster 3 was directly ingested into cells by cell-fusion-like mechanism. According to the cytotoxicity evaluation test, both rhenium clusters 2 and 3 did not exhibit acute cytotoxic effects up to 50 μM, at the practical concentration level of biological applications. It is, therefore, expected that the rhenium cluster complexes can be promising potential candidates as diagnostic agents for medical treatment.

First molecular octahedral rhenium cluster complexes with terminal As- and Sb-donor ligands

Six new molecular octahedral cluster complexes with the general formulas trans-[{Re6(μ3-Q)8}(EPh3)4Br2] and fac-[{Re6(μ3-Q)7(μ3-Br)}(AsPh3)3Br3] (Q = S or Se and E = As or Sb) were synthesized by the reactions of the cesium salts of the [{Re6(μ3−S)8}Br6]4−, [{Re6(μ3-Se)8Br6]3−, and [{Re6(μ3-Q)7(μ3-Br)}Br6]3− anions with molten triphenylarsine (AsPh3) and triphenylantimony (SbPh3), respectively. The compositions and structures of the resulting complexes were established by single-crystal X-ray diffraction and confirmed by elemental analysis and vibrational spectroscopy. The compositions and structures of the complexes depend on the composition of the cluster core in the starting salts. The luminescence spectra were recorded for powdered samples of all these compounds and the earlier described complexes trans-[{Re6Q8}(PPh3)4Br2] and fac-[{Re6Q7Br}(PPh3)3Br3].

Cluster Core Controlled Reactions of Substitution of Terminal Bromide Ligands by Triphenylphosphine in Octahedral Rhenium Chalcobromide Complexes

Reactions of rhenium chalcobromides Cs4[{Re6(mu3-S)8}Br6].2H2O, Cs3[{Re6(mu3-Se)8}Br6].2H2O, Cs3[{Re6(mu3-Q)7(mu3-Br)}Br6].H2O (Q = S, Se), and K2[{Re6(mu3-S)6(mu3-Br)2}Br6] with molten triphenylphosphine (PPh3) have resulted in a family of novel molecular hybrid inorganic-organic cluster compounds. Six octahedral rhenium cluster complexes containing PPh3 ligands with general formula [{Re6(mu3-Q)8-n(mu3-Br)n}(PPh3)4-nBrn+2] (Q = S, n = 0, 1, 2; Q = Se, n = 0, 1) have been synthesized and characterized by X-ray single-crystal diffraction and elemental analyses, 31P{1H} NMR, luminescent measurements, and quantum-chemical calculations. It was found that the number of terminal PPh3 ligands in the complexes is controlled by the composition and consequently by the charge of the cluster core {Re6Q8-nBrn}n+2. In crystal structures of the complexes with mixed chalcogen/bromine ligands in the cluster core all positions of a cube [Q8-nBrn] are ordered and occupied exclusively by Q or Br atoms. Luminescence characteristics of the compounds trans-[{Re6Q8}(PPh3)4Br2] and fac-[{Re6Se7Br}(PPh3)3Br3] (Q = S, Se) have been investigated in CH2Cl2 solution and the broad emission spectra in the range of 600-850 nm were observed.

Octahedral rhenium cluster complexes with organic ligands: Synthesis, structure and properties of [Re 6Q 8(3,5-Me 2PzH) 6]Br 2 · 2(3,5-Me 2PzH) (Q = S, Se)

Two new octahedral cluster complexes – [Re 6S 8(3,5-Me 2PzH) 6]Br 2 · 2(3,5-Me 2PzH) ( 1) and [Re 6Se 8(3,5-Me 2PzH) 6]Br 2 · 2(3,5-Me 2PzH) ( 2), where 3,5-Me 2PzH is 3,5-dimethylpyrazole, have been synthesized using reaction of rhenium chalcobromide complexes Cs 4[Re 6S 8Br 6] · 2H 2O and Cs 3[Re 6Se 8Br 6] · H 2O, respectively, with molten 3,5-dimethylpyrazole. Both compounds synthesized were characterized by X-ray single-crystal diffraction and chemical analysis, IR and luminescent spectra.

[Re6Q7O(3,5‐Me2PzH)6]Br2·3,5‐Me2PzH (Q = S, Se) − New Octahedral Rhenium Cluster Complexes with Organic Ligands: Original Synthetic Approach and Unexpected Ligand Exchange in the Cluster Core

AbstractTwo new octahedral rhenium cluster complexes, [Re6S7O(3,5‐Me2PzH)6]Br2·3,5‐Me2PzH (1) and [Re6Se7O(3,5‐Me2PzH)6]Br2·3,5‐Me2PzH (2), with the organic ligand 3,5‐dimethylpyrazole (3,5‐Me2PzH), have been synthesised by reaction of rhenium chalcobromides Cs3[Re6(µ3‐Q7Br)Br6] (Q = S, Se) with molten dimethylpyrazole. During the reaction, all six apical bromine ligands of the cluster complexes are substituted by the organic ligand, which is coordinated through the aromatic nitrogen atom N2. Additionally, the inner ligand µ3‐Br in the cluster core [Re6(µ3‐Q7Br)]3+ is substituted by oxygen, giving cluster cores [Re6(µ3‐Q7O)]2+ with mixed chalcogen/oxygen ligands. Compounds 1 and 2 have been characterised by single‐crystal X‐ray diffraction analysis. They are isostructural and crystallise with four formula units in the unit cell. Absorption spectra and luminescence characteristics of these two cluster compounds have been investigated in methanol. Absorption starts below 400 nm. For both compounds, broad emissions were found. The fluorescence decays of the two compounds follow a diexponential decay behaviour. The main fluorescence intensity decays have longer fluorescence lifetimes of 3.07 ± 0.03 (1) and 3.96 ± 0.02 µs (2). Studying the thermal stability of both compounds in vacuo showed that the release of 3,5‐dimethylpyrazole ligands begins near 200 °C, and decomposition, with the removal of 7 molecules of 3,5‐Me2PzH, is complete at 330 °C. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Tellurium-containing rhenium cluster complexes

Synthetic procedures as well as the structures and some properties of tetrahedral and octahedral tellurium-containing rhenium cluster complexes are reported. Crystal chemistry of various types of structure is discussed.