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This study aims at the synthesis and initial biological evaluation of novel rhenium–tricarbonyl complexes of 3,3′,4′,5,7-pentahydroxyflavone (quercetin), 3,7,4΄-trihydroxyflavone (resokaempferol), 5,7-dihydroxyflavone (chrysin) and 4΄,5,7-trihydroxyflavonone (naringenin) as neuroprotective and anti-PrP agents. Resokaempferol was synthesized from 2,2΄,4-trihydroxychalcone by H2O2/NaOH. The rhenium–tricarbonyl complexes of the type fac-[Re(CO)3(Fl)(sol)] were synthesized by reacting the precursor fac-[Re(CO)3(sol)3]+ with an equimolar amount of the flavonoids (Fl) quercetin, resokaempferol, chrysin and naringenin and the solvent (sol) was methanol or water. The respective Re–flavonoid complexes were purified by semi-preparative HPLC and characterized by spectroscopic methods. Furthermore, the structure of Re–chrysin was elucidated by X-ray crystallography. Initial screening of the neuroprotective properties of these compounds included the in vitro assessment of the antioxidant properties by the DPPH assay as well as the anti-lipid peroxidation of linoleic acid in the presence of AAPH and their ability to inhibit soybean lipoxygenase. From the above studies, it was concluded that the complexes’ properties are mainly correlated with the structural characteristics and the presence of the flavonoids. The flavonoids and their respective Re-complexes were also tested in vitro for their ability to inhibit the formation and aggregation of the amyloid-like abnormal prion protein, PrPSc, by employing the real-time quaking-induced conversion assay with recombinant PrP seeded with cerebrospinal fluid from patients with Creutzfeldt–Jakob disease. All the compounds blocked de novo abnormal PrP formation and aggregation. Graphical abstract

Continual development of nickel-based superalloys for single-crystal turbine applications has pushed their operating temperatures higher and higher, most notably through the addition of rhenium. However, this has left them susceptible to the precipitation of topologically closed packed phases (TCPs), which are widely considered detrimental. Whilst these have long been reported as an end-of-life phenomenon in in-service components, they have more recently been observed during the manufacture of turbine blades. Several rhenium-containing alloys (CMSX-4, CMSX-10K, and CMSX-10N) were cast into single-crystal test bars and studied at different times along their solution heat-treatment process to discern if, when, and where these TCPs precipitated. It was seen that all alloys were susceptible to TCPs at some point along the process, with the higher rhenium-containing alloy CMSX-10N being the most prone. They occurred at the earliest stages of the solution process; this was attributed to aluminium diffusion from the segregated interdendritic regions into the dendrite core, causing the concentration of rhenium into the ɣ-matrixes until sufficient potential was achieved for TCP precipitation. As the samples became more homogeneous, fewer TCPs were observed; however, in the case of CMSX-10N, this took longer than the typical 24-h solution time used in industry, leading to components entering service with TCPs still present.

In situ prepared lithium arylselenolates {LiSePh, LiSe(2,6-Me2Ph), LiSe(2,4,6-Me3Ph)} or -tellurolates {LiTePh, LiTe(2,6-Me2Ph), LiTe(2,4,6-Me3Ph)} react with [ReOCl3(PPh3)2] and (NBu4)Br in good yields under formation of rhenium(V) complexes of the composition (NBu4)[ReO(L)4)]. The first oxidorhenium(V) complex with four monodentate phenolato ligands, [ReO(2,6-Me2Ph)4]−, was prepared and isolated in crystalline form. This allows a comparison of experimental and computational data of a full series of such compounds with basal O, S, Se and Te donor atoms. Similar reactions with [ReCl3(PPh3)2(CH3CN)] or [ReCl3(PMe2Ph)3] give trigonal bipyramidal rhenium(III) complexes of the compositions [Re(PPh3)(L)3(CH3CN)] or [Re(PPh3)2(L)3] depending on the chalcogenolate applied. The reported oxidorhenium(V) and rhenium(III) complexes were fully characterized by spectroscopic methods and X-ray diffraction. The bonding situation in the rhenium(V) and rhenium(III) chalcogenolates was assessed through density functional theory calculations based on the quantum theory of atoms in molecules (QTAIM), natural bonding orbital (NBO) analysis, charge analysis, the electron localization function (ELF) maps and topological descriptors at the {3,−1} critical points such as metallicities. Expectedly, the ionicity of the rhenium-chalcogen bonds decreases according to all three applied charge models from O to Te. Generally, the Re−Se and Re−Te bonds are more directional in the Re(III) complexes than in the oxidorhenium(V) compounds.

Reactions of [Re(NPhF)Cl3(PPh3)2] ({NPhF}2− = p-fluorophenylimide) with a variety of alkyl and aryl isocyanides have been studied. Different reactivity patterns and products have been obtained depending on the steric and electronic properties of the individual ligands. This involves the formation of 1 : 1 and 1 : 2 exchange products of Re(V) with the general formulae mer-[Re(NPhF)Cl3(PPh3)(isocyanide)] and cis- or trans-[Re(NPhF)Cl3(isocyanide)2]. The stability of the obtained products is correlated with the substitution pattern of the isocyanide ligands. The products have been studied by single-crystal X-ray diffraction and spectroscopic methods, including IR and multinuclear NMR spectroscopy as well as mass spectrometry. The use of partially fluorinated starting materials and ligands allows the modulation of the solubilities of the starting materials and the products as well as the monitoring of the reactions by means of 19F NMR. The attachment of the CF3 or F substituent on the isocyanides gives control over the steric bulk and the electronic properties of the ligands and, thus, their reactivity.

Zwitterionic compounds such as pyridine-containing tellurenyl compounds are interesting building blocks for heterometallic assemblies. They can act as ambiphilic donor/acceptors as is shown by the products of reactions of the zwitterions HpyTeCl2 or HCF3pyTeCl2 with the rhenium(V) complex [ReOCl3(PPh3)2]. The products have a composition of [ReO2Cl(pyTeCl)(PPh3)2] and [ReO2Cl(CF3pyTeCl)(PPh3)2] with central {O=Re=O…Te(Cl)p⏠y}+ units. The Re-O bonds in the products are elongated by approximately 0.1 Å compared with those to the terminal oxido ligands and establish Te…O contacts. Thus, the normally easily assigned concept of oxidation states established at the two metal ions becomes questionable (ReV/TeII vs. ReIII/TeIV). A simple bond length consideration rather leads to a description with the coordination of a mesityltellurenyl(II) chloride unit to an oxido ligand of the Re(V) center, but the oxidation of the tellurium ion and the formation of a tellurinic acid chloride cannot be ruled out completely from an analysis of the solid-state structures. DFT calculations (QTAIM, NBO analysis) give clear support for the formation of a Re(V) dioxide complex donating into an organotellurium(II) chloride and the alternative description can at most be regarded as a less favored resonance structure.

Chapter 1. Previous work with group 5 imido β-diketiminates and rhenium terminal oxo complexes is summarized, which in combination provide the theoretical basis for the subsequent chapters. The overarching hypothesis and goals of this work are stated.Chapter 2. Synthetic access to the first rhenium oxo β-diketiminate is achieved. Subsequently, the oxygen atom transfer (OAT) reactivity of this complex is gauged. It is determined that OAT from this complex is limited to trialkylphosphines of a moderate steric profile (e.g. PEt3), as small trialkylphosphines (e.g. PMe3) bind strongly to the metal center, and larger phosphines (e.g. PPh3) are kinetically limited due to the encumbering β-diketiminate ligand. Nitrene transfer from the β-diketiminate ligand to the metal is also observed, implying an ancillary limitation of this ligand in low valent rhenium complexes at high temperatures.Chapter 3. Attempts to incorporate a cyclopentadienyl ligand into the rhenium oxo β-diketiminate system using NaCp led to the isolation of an olefin-supported rhenium(III) terminal oxo complex. It was found that using SnCp2 rather than NaCp leads to the intended rhenium(V) oxo Cp complex. The reactivity of this rhenium(V) complex suggested that both the Cp ligand and oxo ligand are susceptible to nucleophilic attack, yielding a variety of rhenium(III) complexes. Computational studies suggest some degree of metal-ligand conjugation (“π-loading”) exists between the Cp and oxo ligands in the starting rhenium(V) complex, which supports the observations made during reactivity studies.Chapter 4. The oxygen atom transfer reactivity of a rhenium(III) terminal oxo β-diketiminate complex is evaluated. It is shown that this compound will only transfer its oxo ligand to electrophilic reagents (e.g. isocyanides and CO) rather than nucleophilic ones (e.g. PMe3). A number of rhenium(I) isocyanide and carbonyl complexes are isolated as products of the oxygen atom transfer process. In all, the results suggest that the oxo moiety of the starting rhenium(III) complex behaves as a nucleophile, and has no demonstrable electrophilic character.Chapter 5. Reduction of a cationic rhenium(V) oxo Cp β-diketiminate with metallic sodium yields an anionic rhenium(I) complex that is both strongly reducing and basic. Accordingly, the corresponding neutral rhenium(II) and rhenium(III) hydride complexes are isolated following oxidation and protonation, respectively, of the anionic compound. Combination of the anionic rhenium(I) compound with ZnCl2 formed a tetrametallic Re(I)-Zn(I)-Zn(I)-Re(I) complex where the four metal centers are arranged in a nearly linear fashion. This compound is the first example of a Zn(I) compound to be supported exclusively by bonding to other metal centers. Computational and reactivity studies of this tetrametallic compound are also presented.

Rhenium-based metallodrugs have recently been highlighted as promising candidates for new antibiotics to combat multi-drug resistant (MDR) pathogens. A new class of rhenium(V) dioxo complexes were prepared from readily accessible diphosphine ligands, and have been shown to possess potent activity against

CuO supported catalyst with high valence rhenium doping were specially studied for photoelectrocatalytic reduction of CO2 to small molecular alcohols, which were synthesized by nitrate thermal decomposition method on anatase TiO2 nanotube arrays (TiO2-NTs). Photoelectrochemical measurements indicate that the high valence rhenium doping helps in improving the catalytic activity and selectivity of CuO supported catalysts. For the case of 6 wt% Re-doped CuO/TiO2-NTs calcined at 723 K, the principal products are methanol and ethanol with yield up to 19.9 μmol and 7.5 μmol after 5 h photoelectrocatalysis at external potential of −0.4 V under simulated solar illumination. In contrast, the products catalyzed by undoped CuO/TiO2-NTs are only methanol and formaldehyde. These results indicate that the high valence rhenium doping will promote the alcoholization process and benefit the C C coupling, leading to the selective conversion of CO2 to ethanol. Furthermore, under suitable external potential (-0.5 V) the CO2 conversion product is almost entirely composed of ethanol.

Possible enhancements of DNA damage with light of different wavelengths and ionizing radiation (Rhenium-188—a high energy beta emitter (Re-188)) on plasmid DNA and FaDu cells via psoralen were investigated. The biophysical experimental setup could also be used to investigate additional DNA damage due to photodynamic effects, resulting from Cherenkov light. Conformational changes of plasmid DNA due to DNA damage were detected and quantified by gel electrophoresis and fluorescent staining. The clonogene survival of the FaDu cells was analyzed with colony formation assays. Dimethyl sulfoxide was chosen as a chemical modulator, and Re-188 was used to evaluate the radiotoxicity and light (UVC: λ = 254 nm and UVA: λ = 366 nm) to determine the phototoxicity. Psoralen did not show chemotoxic effects on the plasmid DNA or FaDu cells. After additional treatment with light (only 366 nm—not seen with 254 nm), a concentration-dependent increase in single strand breaks (SSBs) was visible, resulting in a decrease in the survival fraction due to the photochemical activation of psoralen. Whilst UVC light was phototoxic, UVA light did not conclude in DNA strand breaks. Re-188 showed typical radiotoxic effects with SSBs, double strand breaks, and an overall reduced cell survival for both the plasmid DNA and FaDu cells. While psoralen and UVA light showed an increased toxicity on plasmid DNA and human cancer cells, Re-188, in combination with psoralen, did not provoke additional DNA damage via Cherenkov light.

International audience; The low-valent rhenium(I) salt Na[Re(η5-Cp)(BDI)] (BDI = N,N′-bis(2,6-diisopropylphenyl)-3,5-dimethyl-β-diketiminate) was shown to react with various halide and chalcogenolate reagents, leading to the isolation of a series of rhenium(III)–halide and −pseudohalide complexes: Re(X)(η5-Cp)(BDI) (1-X, X = F, Cl, Br, I; 2, X = OTf) and Re(ER)(η5-Cp)(BDI) (3-ER, ER = SBn, SeBn, TePh). The 1H NMR spectra of these complexes displayed sharp resonances shifted several ppm from typical diamagnetic regions, as well as distinct chemical shift trends down both the halide (with the exception of F) and chalcogenolate series, with both Cp and BDI backbone peaks moving downfield with increasing atomic number. Subsequent magnetic susceptibility measurements of the rhenium(III) halides 1-Cl, 1-Br, and 1-I indicated that these complexes display temperature-independent paramagnetism (TIP), with χTIP values of 7.41(44) × 10–4 to 1.50(51) × 10–3 cm3 mol–1. Multireference complete active space self-consistent field (CASSCF) computations incorporating spin–orbit state mixing revealed small energy separations (1.7–3.0 kcal/mol) between thermally isolated ground states and the first excited spin–orbit states for the rhenium halides, confirming that low-lying excited states are responsible for the observed TIP behavior.

p-Fluorophenylisocyanide (CNPhpF) reacts with [Re(CO)5Br] under stepwise exchange of the carbonyl ligands depending on the conditions applied. The reaction stops with the formation of fac-[Re(CO)3Br(CNPhpF)2] in boiling THF. An ongoing carbonyl exchange is observed at higher temperatures, e. g. in refluxing toluene, with the final formation of the [Re(CNPhpF)6]+ cation. The progress of the reactions has been studied by 19F NMR spectroscopy and the structures of [Re(CO)Br(CNPhpF)4] and [Re(CNPhpF)6](BPh4) have been elucidated by X-ray diffraction.

In this work, O- and N-N-bridging complexes of technetium (V), previously known only for rhenium, were obtained for the first time. Tc(V) complexes with pyridazine (pyd), 1,2,4-triazole (trz), 3,5-dimethylpyrazole (dmpz) and pyrimidine (pyr) were obtained. In three complexes [{TcOCl2}2(μ-O)(μ-pyd)2], [{TcOCl2}2(μ-O)(μ-trz)2]·Htrz·Cl and [{TcO(dmpz)4}(μ-O)(TcOCl4)] two technetium atoms are linked by a Tc-O-Tc bond, and in the first two, Tc atoms are additionally linked by a Tc-N-N-Tc bond through the nitrogen atoms of the aromatic rings. We determined the role of nitrogen atom position in the aromatic ring and the presence of substituents on the formation of such complexes. For the first time, a reaction mechanism for the formation of such complexes was proposed. This article details the crystal structures of four new compounds. The work describes in detail the coordination of Tc atoms in the obtained structures and the regularities of the formation of crystal packings. The spectroscopic properties of the obtained compounds and their mother solutions were studied. The decomposition temperatures of the described complexes were determined. An assumption was made about the oligomerization of three-bridged complexes based on the results of mass spectrometry. Through the analysis of non-valent interactions in the structures, π-stacking, halogen-π and CH-π interactions were found. An analysis of the Hirshfeld surface for [{TcOCl2}2(μ-O)(μ-pyd)2], [{TcOCl2}2(μ-O)(μ-trz)2] and their rhenium analogues showed that the main contribution to the crystalline packing is made by interactions of the type Hal···H/H···Hal (45.4–48.9%), H···H (10.2–15.8%), and O···H/H···O (9.4–16.5%).

A new class of rhenium(i)-based double stranded dinuclear monohelicates was self-assembled. Although these helicates contain two organic ligand strands, only one strand is arranged in a helical fashion, which is an unprecedented form in the helicate architecture.

Substitution of apical halide ligands in [{Re6Sei8}Xa6]3- (X = Cl, Br) by benzimidazole (bimzH) accompanied by a self-assembly process leads to the formation of microporous Re6-based hydrogen-bonded organic frameworks (Re6-HOFs) constructed on N-H···X hydrogen bonds and π-π-stacking interactions between bimzH ligands. Re6-HOFs demonstrate sorption properties with a Brunauer-Emmett-Teller surface area of up to 443 m2 g-1 and luminescence with a quantum yield and an emission lifetime of up to 0.16 and 16 μs, respectively. The compounds obtained complement small groups of transition-metal cluster-based HOFs, which are a perspective for the development of multifunctional frameworks.

The work investigates the corrosion behavior of nickel, rhenium, and their alloys in concentrated nonoxidizing and oxidizing acids. The mechanism of the corrosion dissolution of nickel-rhenium alloys in concentrated hydrochloric and nitric acids is proposed. Based on X-ray studies, the predominant dissolution of nickel from the surface of nickel-rhenium alloys is established. Etching occurs mainly from certain edges, especially along the [111] plane. The introduction of rhenium into nickel in an amount of 5, 10, and 20 wt % has an ambiguous effect on the corrosion rate of the entire alloy and, depending on the ratio of nickel and rhenium in the alloy, the corrosion rate of the alloy in nonoxidizing and oxidizing acids can both decrease and increase. An alloy with 20% rhenium is limiting in concentrated hydrochloric acid from the point of view of achieving the required concentration of rhenium on the surface and reducing the rate of dissolution of the alloys. In concentrated nitric acid and aqua regia, an increase in the rhenium content in the alloy above 10% is impractical, since the corrosion rate increases significantly. An increased rate of dissolution of alloys in nitric acid compared to hydrochloric acid is established.

Alzheimer's disease (AD) is associated with the presence of amyloid plaques in the brain mainly comprised of aggregated forms of amyloid-β (Aβ). Molecules radiolabeled with technetium-99m that cross the blood-brain barrier (BBB) and selectively bind to Aβ plaques have the potential to assist in the diagnosis of AD using single-photon emission computed tomography imaging. In this work, three new tetradentate ligands of pyridyl, amide, amine and thiol donors, featuring a styrylpyridyl group that is known to interact with amyloid plaques, were prepared. The new ligands formed charge-neutral and lipophilic complexes with the [Tc═O]3+ and [Re═O]3+ motifs, and two rhenium complexes were characterized by X-ray crystallography. The rhenium(V) complexes interact with synthetic Aβ1-40 and amyloid plaques on human brain tissue. Two of the new ligands were radiolabeled with 99mTc using a kit-based approach, and their biodistribution in wild-type mice was evaluated. The presence of amide donors in the tetradentate ligand increased the stability of the respective [Tc═O]3+ complexes but reduced brain uptake. While the complexes were able to cross the BBB, the degree of uptake in the brain was not sufficient to justify further investigation of these complexes.

Electrocatalytic reduction of carbon dioxide (CO2) by transition-metal catalysts is an attractive means for storing renewably sourced electricity in chemical bonds. Metal coordination compounds represent highly tunable platforms ideal for studying the fundamental stepwise transformations of CO2 into its reduced products. However, metal complexes can decompose upon extended electrolysis and form chemically distinct molecular species or, in some cases, catalytically active electrode deposits. Deciphering the degradative pathways is important for understanding the nature of the active catalyst and designing robust metal complexes for small-molecule activation. Herein, we present a new dicationic rhenium bipyridyl complex capable of multielectron ligand-centered reductions electrochemically. Our in-depth experimental and computational study provides mechanistic insight into an unusual reductively induced Hoffman-type elimination. We identify benzylic tertiary ammonium groups as an electrolytically susceptible moiety and propose key intermediates in the degradative pathway. This investigation highlights the complex interplay between the ligand and metal ion and will guide the future design of metal-organic catalysts.

We report a variety of rhenium complexes supported by bidentate and tridentate phosphinoamine ligands and their use in the formation of the advanced biofuel isobutanol from methanol and ethanol. Rhenium pincer complexes 1-3 are effective catalysts for this process, with 2 giving isobutanol in 35% yields, with 97% selectivity in the liquid fraction, over 16 h with catalyst loadings as low as 0.07 mol %. However, these catalysts show poorer overall selectivity, with the formation of a significant amount of carboxylate salt solid byproduct also being observed. Production of the active catalyst 1d has been followed by 31P NMR spectroscopy, and the importance of the presence of base and elevated temperatures to catalyst activation has been established. Complexes supported by diphosphine ligands are inactive for Guerbet chemistry; however, complexes supported by bidentate phosphinoamine ligands show greater selectivity for isobutanol formation over carboxylate salts. The novel complex 7 was able to produce isobutanol in 28% yield over 17 h. The importance of the N-H moiety to the catalytic performance has also been established, giving further weight to the hypothesis that these catalysts operate via a cooperative mechanism.

Four novel rhenium cluster complexes with the general formula trans-[Re6Q8(ppy)4X2]·n(ppy) (Q = S, Se; X = Cl, Br; ppy = 4-phenylpyridine) are obtained by the interaction of salts Csn[Re6Q8X6]·2H2O (Q = S, n = 4; Q = Se, n = 3; X = Cl or Br) with a 4-phenylpyridine melt. The single-crystal XRD study shows that the structures of these compounds contain molecular fragments trans-[Re6Q8(ppy)4X2] packed together with 4-phenylpyridine solvate molecules and connected with these molecules by weak interactions, including hydrogen bonds and π-stacking of aromatic rings. It is shown that different halide and chalcogenide ligands of the cluster complex form different types of packing. The obtained compounds are insoluble in water and in organic solvents. The crystal samples are luminescent in the red region with emission peaks at 708-718 nm, quantum yields of 0.01-0.03, and emission lifetimes of ~ 4 μs. The electronic structure of these compounds contains ligand-centered LUMO–LUMO+3 levels localized between metal-centered HOMO and LUMO+4 levels.

By a high-temperature reaction of rhenium(III) iodide and red phosphorus with an excess of sodium cyanide followed by recrystallization from an aqueous solution a new tetrahedral [{Re4(PO)4}(CN)12]8– anionic cluster complex is obtained. It is isolated as a salt of the composition Na8[{Re4(PO)4}(CN)12] 18H2O·MeOH. The structure of the obtained compound is determined by X-ray crystallography. The compound crystallizes in the monoclinic crystal system, P21/n space group, unit cell parameters a = 26.826(3) A, b = 11.4975(12) A, c = 29.141(3) A, β = 97.879(2)°, V = 8903.2(16) A3, Z = 8.

The structural features of eleven mononuclear octahedral monooxo [d2-Re(V)] complexes $$\left[ {{\text{ReO}}\left( {{\text{L}}_{{{\text{penta}}}}^{n}} \right)} \right]$$ with pentadentate chelate ligands (3О, 2N), (2O, 3N), (2O, 2N, P), (2O, 2N, S), and (O, 2N, 2S) have been discussed. The О $$\left( {{\text{L}}_{{{\text{penta}}}}^{n}} \right)$$ atoms are always located in trans positions to multiply bonded O(oxo) ligands. It has been found that in nine compounds with negatively charged oxygen atoms of ligands $${\text{L}}_{{{\text{penta}}}}^{n}$$ in trans positions to multiply bonded O(oxo) ligands, the Re–O(L)trans bonds (1.960–2.065 A) are comparable in length, somewhat longer or noticeably shorter than Re–O(L)cis (1.952–2.140 A). These Re–O(L) bonds in trans positions to oxo ligands can be considered as having an increased multiplicity, since they are comparable in length (rather than elongated because of the structural manifestation of the trans-effect of the oxo ligand) with the Re–O(L)cis distances. In this case, we can speak of pseudodioxo complexes containing two ligands (O(oxo) and O(Ltrans)) with an increased order of the Re–O bonds (~2.5 and ~1.5 A, respectively). In the other two complexes, the Re–O(Lpenta)trans bonds (2.200 and 2.252 A) are significantly elongated. In these two cases, we should talk about the structural manifestation of the trans-effect of the multiply linked oxo ligand.

We report the synthesis and characterization of rhenium-group 9 heterobimetallic diazenido species (η

Due to their non-centrosymmetric structure, B20-type compounds have intriguing properties of chiral magnets and are the objects of study of topological spin textures. Among them is a high-pressure phase MnGe, which demonstrates properties of magnetic skyrmions. We report on the synthesis of an Mn1−xRexGe solid solution with the B20 structure, which can be prepared without the application of high pressure. Mn1−xRexGe (x = 0.169(6)) shows unconventional magnetic behavior, where the Neel temperature is only slightly reduced compared to a chiral-lattice helimagnet MnGe.

The previously published oxidorhenium(V) complex [ReOCl(L1)2] (2), equipped with the bidentate phenol-dimethyloxazoline ligand HL1 (2-(4,4-dimethyl-4,5-dihydro-1,3-oxazol-2-yl)-phenol), shows catalytic activity for the reduction of nitrate to nitrite under mild, ambient and aqueous conditions. The reaction operates under an oxygen atom transfer (OAT) mechanism, using dimethyl sulfide SMe2 (DMS) as oxygen acceptor. Experiments with catalytic amounts of 2 and labelled 15NO3– proved the full reduction of 15NO3– to 15NO2– by 15N NMR spectroscopy. For the second reduction step of nitrite NO2–, we have evidence for a single electron reduction to yield paramagnetic NO, as from one nitrate reduction experiment the paramagnetic cis-dioxidorhenium(VI) complex [Re(O)2(L1)2] (3) could be isolated and characterized by single-crystal X-ray diffraction analysis. Such a single electron reduction of nitrite NO2– would yield NO and complex 3 as the oxidation product. In a stoichiometric experiment of 2, 15NO3– and DMS, nitrous oxide 15N2O could be detected as the only 15N containing product by 15N NMR spectroscopy, proving that further reduction beyond NO is possible with pre-catalyst 2. The rhenium species responsible for the reduction to N2O is currently unknown. Most likely, N2O is formed via an intermediate rhenium nitrosyl complex. Experimental data was gathered by 1H and 15N NMR, IR- and UV–Vis spectroscopy, HR-ESI mass spectrometry, X-ray crystallography, and supported by theoretical computations (DFT).

[Re(CO)Br(CNArDArF2)4] and [Tc(CO)Cl(CNArDArF2)4] (ArDArF = 2,6-(3,5-(CF3)2C6H3)2-4-F-C6H2) were prepared by reactions of [Re(CO)5Br] or (NBu4)[Tc2(CO)6(μ-Cl)3] with the sterically encumbered isocy...

For the first time, χ-Al2O3 was investigated as a sorbent for the simultaneous separation of copper and molybdenum from rhenium. This work finds the optimal conditions of the process. In an acetate...

Bimetallic nitrogen (N2) splitting to form metal nitrides is an attractive method for N2 fixation. Although a growing number of pincer-supported systems can bind and split N2, the precise relationship between the ligand properties and N2 binding/splitting remains elusive. Here we report the first example of an N2-bridged rhenium(III) complex, [(trans-P2tBuPyrr)ReCl2]2(μ-η1:η1-N2) (P2tBuPyrr = [2,5-(CH2PtBu2)2C4H2N]-). In this case, N2 binding occurs at a higher oxidation level than that in other reported pincer analogues. Analysis of the electronic structure through computational studies shows that the weakly π-donor pincer ligand stabilizes an open-shell electronic configuration that leads to enhanced binding of N2 in the bridged complex. Utilizing SQUID magnetometry, we demonstrate a singlet ground state for this Re-N-N-Re complex, and we offer tentative explanations for antiferromagnetic coupling of the two local S = 1 sites. Reduction and subsequent heating of the rhenium(III)-dinitrogen complex leads to chloride loss and cleavage of the N-N bond with isolation of the terminal rhenium(V) nitride complex (P2tBuPyrr)ReNCl.

The interaction of rhenium(III) halides Re3Br9 and Re3I9 with aqueous solution of sodium cyanide resulted in the formation of the first trinuclear halide-cyanide rhenium cluster complexes [{Re3X3}(CN)9]5-/[{Re3X3}(CN)9]4- (X = Br or I) crystallized as salts of the compositions Cs4Na[{Re3Br3}(CN)9]·5.25H2O (1), Cs4Na[{Re3I3}(CN)9]·6H2O (2), Cs4[{Re3Br3}(CN)9]·2H2O·0.5CsCl (3), and Cs4[{Re3I3}(CN)9]·(4). All of the compounds are stable in air in the solid state and in aqueous solution. The substitution of apical halide ligands in the parent compounds Re3X9 by cyanides led to reduction of the original metallocluster Re39+ (12 cluster valence electrons (CVEs)) to Re37+ (14 CVEs), forming the compounds 1 and 2. The apical CN- ligands affect the electronic structure of the Re3 metallocluster stabilizing reduced form. Complexes 1 and 2 represent the first examples of triangular rhenium clusters with the Re37+ metallocluster. The reaction of 1 and 2 with H2O2 resulted in formation of compounds 3 and 4 with the formal charge of the Re3 metallocluster equal to 8+, and no further oxidation to Re39+ occurred. The compounds were characterized by the X-ray diffraction analysis, NMR and UV-vis spectroscopies, mass spectrometry, cyclic voltammetry, and magnetic susceptibility measurements.

The synthesis and structural characterization of a series of supramolecular complexes of bicyclic cationic pyridine-fused 1,2,4-selenodiazoles with various anions is reported. The binding of trifluoroacetate, tetrachloroaurate, tetraphenylborate, perrhenate, and pertechnetate anions in the solid state is regarded. All the anions interact with selenodiazolium cations exclusively via a pair of “chelating” Se⋯O and H⋯O non-covalent interactions, which make them an attractive, novel, non-classical supramolecular recognition unit or a synthon. Trifluoroacetate salts were conveniently generated via novel oxidation reaction of 2,2′-dipyridyl diselenide with bis(trifluoroacetoxy)iodo)benzene in the presence of corresponding nitriles. Isolation and structural characterization of transient 2-pyridylselenyl trifluoroacetate was achieved. X-ray analysis has demonstrated that the latter forms dimers in the solid state featuring very short and strong Se⋯O and Se⋯N ChB contacts. 1,2,4-Selenodiazolium trifluoroacetates or halides show good solubility in water. In contrast, (AuCl4)−, (ReO4)−, or (TcO4)− derivatives immediately precipitate from aqueous solutions. Structural features of these supramolecular complexes in the solid state are discussed. The nature and energies of the non-covalent interactions in novel assembles were studied by the theoretical methods. To the best of our knowledge, this is the first study that regards perrhenate and pertechnetate as acceptors in ChB interactions. The results presented here will be useful for further developments in anion recognition and precipitation involving cationic 1,2,4-selenodiazoles.

Eight rhenium(i) N-heterocyclic carbene complexes in combination with N-acetyl amino acids ligands have been synthesised. The aquation rate constants for the complexes were evaluated and these compounds were cytotoxic in three cancer cell lines.