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A tripodal anion receptor has been obtained by an easy and fast single-reaction synthesis from commercial reagents. The three ligand arms-bearing aromatic groups able to form anion–π interactions define ligand clefts where large anions, such as perchlorate and perrhenate, are included. We report here the synthesis of the ligand, its acid/base properties in an aqueous solution which has been used to direct the synthesis of anion complexes, and the crystal structure of the free ligand and its anion complexes H3L(ClO4)2·H2O and H3L(ReO4)2.

The β- emitter, rhenium-188 (188Re), has long been recognized as an attractive candidate for targeted cancer radionuclide therapy (TRNT). This transition metal shares chemical similarities with its congener element technetium, whose nuclear isomer technetium-99m (99mTc) is the current workhorse of diagnostic nuclear medicine. The differences between these two elements have a significant impact on the radiolabelling methods and should always receive critical attention. This review aims to highlight what needs to be considered to design a successful radiopharmaceutical incorporating 118Re. Some of the most effective strategies for preparing therapeutic radiopharmaceuticals with 188Re are illustrated and rationalized using the concept of the inorganic functional group (core) and a simple ligand field theoretical model combined with a qualitative definition of frontiers orbitals. Of special interest are the Re(V) oxo and Re(V) nitrido functional groups. Suitable ligands for binding to these cores are discussed, successful clinical applications are summarized, and a prediction of viable future applications is presented. Rhenium-188 decays through the emission of a high energy beta particle (2.12 MeV max energy) and a half-life of 16.9 h. An ideal biological target would therefore be a high-capacity target site (transporters, potential gradients, tumour microenvironment) with less emphasis on saturable targets such as overexpressed receptors on smaller metastases. ispartof: MOLECULES vol:28 issue:3 ispartof: location:Switzerland status: published

Cationic metal-organic framework (MOF) materials are widely used in the anion separation field, but there are few reports of pyrimidyl ligands as building units. In this work, three new cationic MOFs based on pyrimidyl as functional group ligands were synthesized for the removal of radioactive pertechnetate from aqueous solution. The pyrimidyl ligands were designed by incorporating pyrimidyl units into the skeletons of benzene, triphenylamine, and tetraphenylethylene, respectively. Taking advantage of multiple coordination sites of pyrimidyl groups, three cationic MOFs (ZJU-X11, ZJU-X12, and ZJU-X13) with diverse structures were solvothermally synthesized using silver ion as the metal node. Scanning electron microscopy-energy-dispersive spectroscopy mapping demonstrated that these three cationic MOFs could capture ReO4- via anion exchange, but the sorption capabilities were distinctly different. With 95% removal toward ReO4-, ZJU-X11 showed the strongest anion-exchange competence among the three MOFs. According to the results of batch experiments, ZJU-X11 could achieve sorption equilibrium within 10 min, remove 518 mg of ReO4- per 1 g of ZJU-X11, remove most of ReO4- after four recycles, and maintain satisfactory selectivity in the presence of excess competing anions, which is one of the best MOF materials for removing ReO4-/TcO4- among the three cationic MOFs. This work indicates that the pyrimidyl group is a promising multiple site to build versatile cationic MOFs.

In this communication experimental and theoretical results are reported affording strong evidence that interactions between electron rich atoms and the metal of tetroxide anions of group 7 elements are a new case of attractive and σ-hole interactions. Single crystal X-ray analyses, molecular electrostatic potentials, quantum theory of atoms-in-molecules, and noncovalent interaction plot analyses show that in crystalline permanganate and perrhenate salts the metal in Mn/ReO4- anion can act as electron acceptors, the oxygen of another Mn/ReO4- anion can act as the donor and supramolecular anionic dimers or polymers are formed. The name matere bond (MaB) is proposed to categorize these noncovalent interactions and to differentiate them from the classical metal-ligand coordination bond.

For the preference in nuclear energy, one of the high-level liquid waste materials in the form of pertechnetate anion (TcO4-) has become an environmental hazard due to its mobility into groundwater and soil. For its sequestration, numerous efforts have been reported in recent years. However, its selective sensing, even using its nonradioactive surrogate oxidizing perrhenate ion (ReO4-), in aqueous media is very limited. To develop novel materials for such a purpose, we have designed an amino acid-functionalized bent dicarboxylic acid, 4-(((4-((carboxymethyl)carbamoyl)phenyl)amino)methyl)benzoic acid (H2hipamifba), for the strategic room-temperature synthesis of two isostructural and highly luminescent two-dimensional (2D) metal-organic coordination networks (MOCNs), {[Cu(hipamifba)(4,4'-azbpy)]·2CH3OH·2H2O}n (1) and {[Zn(hipamifba)(4,4'-azbpy)]·2CH3OH·2H2O}n (2), where 4,4'-azobipyridine (4,4'-azbpy) as a pillar linker imparts luminescent properties in the architectures. The single-crystal X-ray structural analysis demonstrates that 1 and 2 have pillared-bilayer 2D networks with the sq1/Shubnikov tetragonal plane net topology. These multiresponsive luminescent materials were gainfully employed for the selective sensing of ReO4- in water with a detection limit of 3.4 and 5.4 ppm for 1 and 2, respectively. It is noteworthy to point out that these are the first neutral sensors for such study as the only other two sensors reported in the literature are cationic in nature. Their suitability (selectivity, stability, and recyclability) as excellent water-stable sensors was established through the competitive analyte test and a comparison of pristine and spent samples by powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). Further, the mechanism of selective detection is explained by the time-resolved studies and density functional theory (DFT) calculations.

The thermal analysis behavior of C6H6N3[ReO4] was studied by simultaneous thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) up to 700 °C under argon. Such analysis afforded rhenium metal, which was characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy. XRD peak broadening due to crystallite size and lattice strain was analyzed by both Williamson-Hall (W-H) and Debye-Scherrer (D-S) methods. Efforts to isolate Re metal from the thermal treatment of benzotriazole (BTA = C6H5N3) with NH4ReO4 and Re2O7 under various atmospheres and temperatures are also reported. The results provide a significant insight into the chemistry of group VII transition metals, investigate the potential use of benzotriazole as a reducing agent for metal productions, and demonstrate a successful convenient method for rhenium metal production, which could be applied to other refractory metals.

Herein, copper perrhenate (Cu(ReO4)2) was synthesized using a micro-emulsion method and adhered to graphene (Gr) using an ultrasonic process. Then, the as-prepared Cu(ReO4)2/Gr composite was added into the synthetic oil as a lubricant additive with the help of ionic liquid to achieve enhanced dispersion stability within the base oil. The tribological performances of the Cu(ReO4)2/Gr additive were investigated using four-ball tests and the ball-on-disk reciprocating configuration under various temperatures. The potential lubrication mechanisms of the Cu(ReO4)2/Gr additive were performed using a series of characterization methods including XRD, Raman, SEM-EDS, TEM, DSC/TG, and XPS. The results of four-ball tests at room temperature indicated that the Cu(ReO4)2/Gr additive could substantially improve the tribological performances of the base oil. The smallest coefficient of friction (COF) and wear scar diameter (WSD) values were 0.068 and 495 μm, respectively, when 0.05 wt% of Cu(ReO4)2/Gr was added. Additionally, the graphene accelerated friction-induced heat transfer, which led to decreased friction and wear. The results of reciprocating friction experiments at elevated temperatures revealed that the Cu(ReO4)2/Gr additive had excellent friction-reduction properties when the temperature was high. This could be attributed to the generation of a protective layer containing tribo-oxides from the alloy, some residual carbides and copper perrhenate induced by friction heat and stress. This protective layer was uniformly and stably covered on the worn surface, which could effectively alleviate direct contact between the rubbing pair.

The effective removal of radioactive 99TcO4- anion from nuclear wastewater remains a very difficult unsolved problem. Functional adsorbent materials with high stability, anion-exchange capacity, excellent selectivity, and recyclability are much needed to solve this problem. In this work, we designed two stable cationic metal-organic frameworks (MOFs)-Zr-tcbp-Me and Zr-tcpp-Me-for possible use as adsorbent materials to remove 99TcO4-. Both compounds were synthesized by solvothermal reactions of the tetracarboxylate ligand with zirconium salt, followed by postsynthetic modification (N-methylation). The crystallinity of both zirconium-based MOFs can be well retained under harsh conditions, and they exhibit high adsorption capacity and selectivity toward ReO4- anion, a nonradioactive analogue of 99TcO4-. Zr-tcbp-Me and Zr-tcpp-Me demonstrate the highest framework stability toward acidity among all previously reported cationic MOFs that have been tested for perrhenate removal from wastewater.

99Tc is one of the most abundant radiotoxic isotopes in used nuclear fuel with a high fission yield and a long half-life. Effective removal of pertechnetate (TcO4-) from an aqueous solution is important for nuclear waste separation and remediation. Herein, we report a series of facilely obtained benzene-linked guanidiniums that could precipitate TcO4- and its nonradioactive surrogate ReO4- from a high-concentration acidic solution through self-assembly crystallization. The resulting perrhenate and pertechnetate solids exhibit exceptionally low aqueous solubility. The benzene-linked guanidiniums hold one of the highest TcO4- removal capacities (1279 mg g-1) among previously reported materials and possess a removal percentage of 59% for ReO4- in the presence of Cl- over 50 times. The crystallization mechanism was clearly illustrated by the single-crystal structures and density functional theory calculations, indicating that TcO4- is captured through a charge-assisted hydrogen bonding interaction and stabilized by π-π stacking layers. In addition, the removal process is easily recycled and no toxic organic reagents are introduced. This work provides a green approach to preliminarily separate TcO4- from high-level nuclear wastes.

Allylic alcohols form perrhenate esters upon reaction with Re2O7 or HOReO3. These species undergo nonstereospecific and nonregiospecific alcohol-transposition reactions through cationic intermediates. Sequencing these nonselective processes with reversible trapping by electrophiles results in cyclization reactions where regio- and stereocontrol are dictated by thermodynamics. The cationic intermediates can also be utilized as electrophiles in intra- or intermolecular dehydrative reactions with nucleophiles. These processes serve as the basis for applications in catalytic syntheses of a wide range of heterocyclic and carbocyclic structures that often show considerable increases in molecular complexity. This Account describes a sequence of events that started from a need to solve a problem for the completion of a natural product synthesis and evolved into a central element in the design of numerous new transformations that proceed under mild conditions from readily accessible substrates.1 Introduction2 Exploratory Studies3 Application to Spiroketal Synthesis4 Reactions with Epoxides as Trapping Agents5 Development of Dehydrative Cyclizations6 Bimolecular Reactions7 Spirocyclic Ether Formation8 Conclusions

A new imidazolium functionalized hexapodal polymeric receptor, [PHIm-Br], showed selective and efficient removal (>99%) of perrhenate (ReO4−), from 100% aqueous medium via solid–liquid extraction, which was 13% higher as compared to its monomeric analouge [HIm-Br]. Most importantly, [PHIm-Br] overcomes the drawback of [HIm-Br] in terms of removal of ReO4− at lower anion concentration of ∼100 ppm along with excellent radiation resistivity and reusability within a wide pH range, which implies its potential towards practical applications.

The corrosion characteristics of thin coatings (5 µm) with binary and ternary alloys CoW, CoRe, CoWRe, obtained from poly-ligated citrate-pyrophosphate electrolyte, depending on the concentration of potassium perrhenate, were investigated. The methods of impedance spectroscopy and voltammetry have shown that the most corrosion-resistant coatings were obtained with a current density of 10 mA·cm−2. The largest value of corrosion resistance and microhardness is inherent in the CoWRe alloy and is 3.2 kΩ·cm2 in 1 M KOH solution and 644 HV. It has been found that an increase in the rhenium content in the alloy results in an increase in the current efficiency (CE) during the precipitation of the alloy from the alkaline citrate-pyrophosphate electrolyte and CE reaches 84%.

Results are provided for thermal and thermogravimetric studies of lead sludge in the presence of and without oxidizing agents in order to determine the thermally active part of the charge composition. It is shown that during oxidation firing of lead sludge the process begins with charge dewatering and organic compound decomposition, and rare metal oxidation commences after complete destruction of organic compounds. Addition of sodium nitrate or calcium hypochlorite oxidizing agents provides complete oxidation of rhenium and osmium in the range of 400–650°C with the subsequent extraction of osmium into sublimate and concentration of rhenium in the form of perrhenate compounds in the ash. In this case decomposition of organic substances proceeds in parallel with oxidation reactions of rare metals without affecting their oxidation.

Re2O7 in hexafluoroisopropyl alcohol provides access to cationic intermediates from alcohols through the intermediacy of perrhenate esters. This manuscript describes the application of the system to the formation of a number of weakly basic heterocyclic systems through dehydration reactions and intramolecular nucleophilic addition. The influence of the substrate structure on the reaction rates and stereocontrol is discussed with respect to intermediate ion pairs.

In this work, an ion imprinted polymer (ReO4–-IIP) of the perrhenate ion based on acrylamide (AM) and acrylic acid (AA) was prepared by solution polymerization using ReO4– as a template ion, N,N-me...

The extraction behavior of uranyl from the nitric acid medium using an asymmetric diglycolamide, DMDODGA, in BmimNTf2 was studied. The effects of the concentration of HNO3, DMDODGA and temperature on the distribution ratio were discussed. The distribution ratio of uranyl into BmimNTf2 liquid is much higher than that into hydrocarbon diluents. The extraction mechanism was investigated by UV-visible spectroscopic and extraction experiments that all agree the cation-exchange mechanism. Formation of the 1:2 U/DMDODGA complexes was analyzed using the slope analysis method. In addition, uranyl can be effectively separated from perrhenate using DMDODGA-BmimNTf2 system.

The temperature-dependent structure-property relationships of the aluminosilicate perrhenate sodalite |Na8(ReO4)2|[AlSiO4]6 (ReO4-SOD) were analysed via powder X-ray diffraction (PXRD), Raman spectroscopy and heat capacity measurements. ReO4-SOD shows two phase transitions in the investigated temperature range (13 K T P 4 ¯ 3 n $P\overline{4}3n$ (> 218.6(1 K) to a statically disordered ( P 4 ¯ 3 n $P\overline{4}3n$ . The loss of the dynamics of the template anion during cooling causes an increase of disorder, indicated by an unusual intensity decrease of the 011-reflection and an increase of the Re-O2 bond length with decreasing temperature. Additionally, Raman spectroscopy shows a distortion of the ReO4 anion. Upon heating the thermal expansion of the sodalite cage originated in the tilt-mechanism causes the second phase transition at 442(1) K resulting in a symmetry-increase from P 4 ¯ 3 n $P\overline{4}3n$ to P m 3 ¯ n $Pm\overline{3}n$ , the structure with the sodalites full framework expansion. Noteworthy is the high decomposition temperature of 1320(10) K.

Computationally designed ion imprinted polymers (IIP) were synthesised for selective binding of perrhenate ion from CMSX-4 superalloy leach solutions. A library of functional monomers was screened using Density Functional Theory (DFT) based on their binding energy with perrhenate ion. DFT calculations were also employed to determine the template:monomer ratio of 1:2 from binding energy calculation of the complex formed, and perrhenate ion formed the most stable complex with protonated 4-vinylpyridine (4VP) at 1:2 molecular ratio. An optimum imprinting ratio of 2:4:40 for the functional monomer:cross-linker:perrhenate ion template was calculated using molecular dynamics simulation of a fixed number of component molecules in a periodic boundary and isothermal conditions (NVT-Molecular Dynamics) using MM+ force field. The perrhenate ion selective IIPs were synthesised via bulk polymerisation and combinatorial screening of the imprinting porogen composition was employed to compliment the computational screening. The resulted IIPs showed fast kinetics, high binding capacity (122 mg Re/g polymer), and adsorption processes governed by pseudo-second order kinetics. The IIP synthesised using 4-vinylpyridine and ethylene glycol dimethylacrylate (EGDMA) show superior selectivity towards perrhenate ion in the presence of the oxides, hydroxides, and chlorides of Al, Co, Cr, Hf, Mo, Ni, Ta, Ti, and W in the feed leach solution at pH = 7.0. The perrhenate ion IIPs demonstrated excellent chemical and physical stability towards extreme acidic stripping conditions, and storage for an extended period. Therefore, the use of perrhenate ion imprinted polymers for separation as part of the industrial recycling of rhenium from superalloy leach solutions is recommended.

The theoretical description of a new sandwich-like rhenium-based polymer composite cathodic electrodeposition has been given. The cathodic process is realized by perrhenate-ion electrochemical reduction to rhenium (IV) oxide, acting as an in situ formed oxidant for 3,4-dimethoxypyrrole polymerization. It is shown that the polymer deposition in this system is realized by more efficient manner than during the direct electropolymerization. The polymer composite has to have a well-developed morphology and enhanced conductivity by sandwich-like structure. The oscillatory behavior, in this case, is also possible, being caused by the DEL influences on both electrochemical and chemical stages of the process. DOI: http://dx.doi.org/10.17807/orbital.v12i2.1193

The strength of hydrogen bonding to and structure of hydrated oxometallate ions in aqueous solution have been studied by double difference infrared (DDIR) spectroscopy and large-angle X-ray scattering (LAXS), respectively. Anions are hydrated by accepting hydrogen bonds from the hydrating water molecules. The oxygen atom of the permanganate and perrhenate ions form weaker and longer hydrogen bonds to water than the hydrogen bonds in bulk water (i.e., they act as structure breakers), while the oxygen atoms of the chromate, dichromate, molybdate, tungstate, and hydrogenvanadate ions form hydrogen bonds stronger than those in bulk water (i.e., they act as structure makers). The oxometallate ions form one hydration shell distinguishable from bulk water as determined by DDIR spectroscopy and LAXS. The hydration of oxoanions results in X–O bond distances ca. 0.02 Å longer than those in unsolvated ions in the solid state not involved in strong bonding to counterions. The oxygens of oxoanions with a central atom from the second and third series in the periodic table and the hydrogenvanadate ion hydrogen bind three hydrating water molecules, while oxygens of oxoanions with a heavier central atom only form hydrogen bonds to two water molecules., The strength of the hydrogen bonding to and the structure of hydrated oxometallate ions in aqueous solution have been studied by double difference infrared spectroscopy and large-angle X-ray scattering, respectively.

In this article, nano-sized calcium perrhenate was prepared using the microemulsion reaction method. By the aid of surfactant, the calcium perrhenate was suspended in pentaerythritol ester base oil to serve as a lubricating additive. The tribological performances of the oil containing calcium perrhenate at elevated temperatures were investigated by four-ball tests and ball-on-disk reciprocating sliding tests. The underlying lubricating mechanism of the calcium perrhenate additive was explored using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, differential scanning calorimetry/thermogravimetry, Raman spectroscopy, and X-ray photoelectron spectroscopy. The four-ball test results indicated that the oil containing calcium perrhenate featured lower friction coefficients, smaller wear scar diameters, and lower temperature rising performance than the base oil under an applied load of 392 N. The optimum lubricating property was obtained when the additive was at a concentration of 0.05 wt%. The tribological performance in a wide temperature range results showed that the friction coefficients of the oil containing calcium perrhenate were slightly lower than those of the base oil at a relatively low temperature range, and decreased as the temperature increased within a high range. The improved tribological performances owed to the formation of a protective layer, which consisted of the shear-susceptible calcium perrhenate additive as well as some native metal oxides that enhanced the layer carrying capacity during rubbing after chemical degradation of base oil. This protective layer acted as a barrier between the rubbing surfaces, preventing them from directly contacting each other at elevated temperatures.

Abstract Carbon aerogels are unique type of amorphous carbon-based materials with an extraordinary properties including light weight, well-developed and tailored pore structure, high specific surface area, low electrical resistivity and high purity. Therefore carbon aerogels can be used in numerous applications, including energy storage materials such as supercapacitors or lithium-ion batteries. Synthesis of hydrogel requires accurate concentration of monomers and catalysts, exact temperature and time. Low-density carbon aerogel can be produced using a complicated supercritical drying method, which allows to expel solvent without carbon porous structure collapse. Here we report a possibility to use novel type of resorcinol/formaldehyde gelation catalyst based on rhenium salt. The organic gel obtained using lithium perrhenate was traditionally carbonized and examined with respect to energy storage properties. It was found that interaction of lithium and rhenium atoms with monomers resulted in completely different structure than using typical sodium carbonate catalyst. Graphic abstract

The extraction process of rhenium was investigated in the room-temperature ionic liquid 1-pentyl-3-methylimidazolium bis((trifluoromethane)-sulfonyl)imide ([C5mim][NTf2]) containing N235. At ionic strength ranging from 0.2 to 2.0 mol·kg–1 and temperatures ranging from 293.15 to 318.15 K, the molalities of perrhenate in the aqueous phase were obtained at an extraction equilibrium. The standard extraction constants K0 at diverse temperatures were gained by the Pitzer polynomial approximation method. Thermodynamic characters for the extraction procedure were calculated.

Highly selective anion recognition and extraction are critical and challenging to deep removal of pollutants from the environment and effective recovery of valuable chemicals from low–content (at sub–ppm or ppb level) sources. Herein, we detail the gram–scale synthesis of a superphane 2, a new supramolecular host that was found capable of encapsulating ReO4– with high selectivity, as suggested by the single–crystal structures, NMR spectroscopy and theoretical calculations. Under solid–liquid extraction condidtions, 2 proved able to extract perrhenate from the solid mixture containing trace ReO4– (as low as 200 ppb) with near 100% selectivity over other 7 competing anions. Under liquid–liquid extraction conditions, using 2 as the supramolecular extractant, over 99.99% of ReO4– could be separated from the complex simulated aqueous waste streams containing ppm–level perrhenate and large excess of competing ions. Notably, after extraction, 2 could be recycled and reused by simple treatment with NaHCO3. This study opens up the door to development of superphane–based advanced materials for deep elimination of pollutants from the envirenment and purification of chemicals of interest with high efficiency and selectivity.

Liquid-liquid extraction for the removal of pertechnetate (99TcO4-) and perrhenate (ReO4-) is reported based on using the tripodal extractant N,N,N',N',N″,N″-hexa-n-octylnitrilotriacetamide (HONTA) composed of three amide groups and a tertiary amine. The extraction behaviors were compared with those using alkyldiamideamines (ADAAM(Oct) and ADAAM(EH)), and the commercial amine-type extractant, trioctylamine (TOA). HONTA quantitatively extracted 99TcO4- and ReO4- in the pH range from 1.0 to 2.5 by the co-extraction of protons. The extraction performance of the extractants was improved in the order of HONTA > ADAAM(Oct) > ADAAM(EH) > TOA. 99TcO4- and ReO4- in the extracting phase were successfully stripped using neutral aqueous solutions as the receiving phase, and the extraction ability of HONTA was maintained after five repeated uses.

The voltage drops across the elements of a three-chamber electrolytic cell are measured during the synthesis of perrhenic acid from potassium perrhenate, and the main contribution to the total bath voltage is shown to be made by the central chamber solution because of the low solubility of potassium perrhenate. The direct electrodialysis recovery of rhenium from the alkaline electrolytes formed during the anodic dissolution of tungsten–rhenium alloys is found to be unreasonable because of a rapid decrease in the process rate and high electric power consumption. The cleaning of tungsten–rhenium electrolytes from tungsten for the subsequent recovery of rhenium from a solution in the form of perrhenic acid is tested. The application of this technological sequence is shown to decrease the electric power consumed for electrodialysis fivefold and to decrease the rhenium losses die to the elimination of the stage of precipitation of potassium perrhenate. A fundamental technological scheme of the process is proposed.

We report the structural, spectroscopic, and computational studies of two new Re(I) tricarbonyl complexes bearing 2,3,6,7-tetraphenyl-1,4,5,8-tetraazaphenanthrene (Ph4TAP) and 4,5-diazafluoren-9-one (dafone) having a coordinated perrhenate group obtained via in situ superoxidation of Re(I) to Re(VII); intramolecular and intermolecular n → π* interactions are dominant and stabilize the molecular geometry and crystal packing.

New coordination compounds of iron(II) sulfate, hexafluorosilicate, and perrhenate with 2,6-bis(benzimidazole-2-yl)pyridine (L), namely, [FeL2]SO4 ∙ H2O (I), [FeL2]SiF6 ∙ H2O (II), and [FeL2](ReO4)2 ∙ 1.5H2O (III) have been synthesized. The complexes have been studied by static magnetic susceptibility, electronic (diffuse reflectance), IR, and Mossbauer spectroscopy, and X-ray diffraction. The μeff(T) study of dehydrated complexes I–III (1–3) within the range 80–520 K has shown the spin transition 1А1 ⇔ 5Т2. A two-stage transition is observed in complex 1, whereas one-stage transitions occur in complexes 2 and 3. The forward spin transition temperatures (Тс↑) of complexes 1–3 are 423 and 503, 476, 362 K, respectively. Complex 3 sustains an abrupt spin transition with a hysteresis in the μeff(T) curve (ΔT = 21 K).

The anions pertechnetate, TcO4-, and perrhenate, ReO4-, exhibit very similar chemical and physical properties. Revealing and understanding disparities between them enhances fundamental understanding of both. Electrospray ionization generated the gas-phase proton bound dimer (TcO4-)(H+)(ReO4-). Collision induced dissociation of the dimer yielded predominantly HTcO4 and ReO4-, which according to Cooks' kinetic method indicates that the proton affinity (PA) of TcO4- is greater than that of ReO4-. Density functional theory computations agree with the experimental observation, providing PA[TcO4-] = 300.1 kcal mol-1 and PA[ReO4-] = 297.2 kcal mol-1. Attempts to rationalize these relative PAs based on elementary molecular parameters such as atomic charges indicate that the entirety of bond formation and concomitant bond disruption needs to be considered to understand the energies associated with such protonation processes. Although in both the gas and solution phases, TcO4- is a stronger base than ReO4-, it is noted that the significance of even such qualitative accordance is tempered by the very different natures of the underlying phenomena.

The structures and dynamics of quinuclidinium perrhenate, which is the first example of a plastic/ferroelectric crystal, were investigated by molecular dynamics simulation. Our simulation results s...

A polyligand citrate-pyrophosphate electrolyte is proposed, which makes it possible to obtain uniform bright coatings containing 15–40 at.% Re and 10–4 at.% W and a current efficiency of up to 93% depending on the concentration of potassium perrhenate in the solution. The dependence of the chemical composition, current efficiency and morphology of ternary electrolytic alloys CoWRe on the electrolyte components and the electrolysis conditions is presented. The coatings obtained are fine-crystalline and X-ray amorphous and have a high microhardness of 574–788 HV.

The title hydrated salt, tris­[hexa­amminecobalt(III)] tetroxidorhenate(VII) tetra­kis­[hexa­fluorido­rhenate(IV)] hexa­hydrate, arose unexpectedly due to possible contamination of the K2ReF6 starting material with KReO4. It consists of octa­hedral [Co(NH3)6]3+ cation (Co1 site symmetry 1), tetra­hedral [ReVIIO4]− anions (Re1 site symmetry 1) and octa­hedral [ReIVF6]2− anions (Re site symmetries, Re2: 1; Re3 and Re4: ). A network of N—H⋯F hydrogen bonds consolidates the structure., The title hydrated salt, tris­[hexa­amminecobalt(III)] tetraoxidorhenate(VII) tetra­kis­[hexa­fluorido­rhenate(IV)] hexa­hydrate, arose unexpectedly due to possible contamination of the K2ReF6 starting material with KReO4. It consists of octa­hedral [Co(NH3)6]3+ cation (Co1 site symmetry 1), tetra­hedral [ReVIIO4]− anions (Re site symmetry 1) and octa­hedral [ReIVF6]2− anions (Re site symmetries 1and ). The [ReF6]2− octa­hedral anions (mean Re—F = 1.834 Å), [Co(NH3)6]3+ octa­hedral cations (mean Co—N = 1.962 Å), and the [ReO4]− tetra­hedral anion (mean Re—O = 1.719 Å) are slightly distorted. A network of N—H⋯F hydrogen bonds consolidates the structure. The crystal studied was refined as a two-component twin.

Counterions have a significant effect on the efficiency of the deoxydehydration (DODH) reaction. Four perrhenate salts, Z+ReO4− (Z = Na+, K+, NH4+, and Bu4N+), were tested in the DODH reaction of a vicinal diol in the presence of PPh3 as the reductant. In addition, a new perrhenate salt, (2-ppyH)[ReO4] (2-ppyH+ = 2-phenylpyridinium cation), has been synthesized and characterized by X-ray crystallography and utilized as an efficient catalyst in the DODH reaction. Since so far computational studies related to the influence of the counterion in the different steps of the DODH mechanism are scarce, we have carried out a comparative investigation of the counterion effect using density functional theory (DFT) calculations. The DODH mechanism of the conversion of phenyl-1,2-ethanediol to styrene in the presence of the five perrhenate salts mentioned above, as well as bare perrhenate (ReO4−) was studied from an energetic point of view. The catalytic tests and concomitant DFT computations confirmed the general mechanistic aspect in which the counterion plays an active role in all stages of the reaction mechanism including intermediate structures, Gibbs free energy changes (ΔG°g and ΔG°sol), transition states, and activation barrier energies. The role of counterion type has been considered in three key steps of the reaction mechanism, including the proton-transfer from diol to oxo-ligand in the rhenium moiety, the nucleophilic attack of the P atom from PPh3 on the oxo-ligand, the dissociation of the OPPh3 ligand, and the olefin extrusion from the Re(V)-diolate intermediate for each perrhenate salt. The crucial roles played by the counterion in terms of structure arrangement during transition states and the activation energy barriers are finally discussed.

Technetium-99 (99Tc) is a major contaminant at nuclear power plants and several US Department of Energy sites. Its most common aqueous species, pertechnetate (TcO4-), is very mobile in the environment, and currently there are no effective technologies for its sequestration. In this work, a porous iron (pFe) material was investigated for TcO4- and perrhenate (ReO4-) sequestration from artificial groundwater. The pFe was significantly more effective than granular iron for both TcO4- and ReO4- sequestration under oxic conditions. The Tc removal capacity was 27.5 mg Tc/g pFe at pH ˜6.8, while the Re removal capacity was 23.9 mg Re/g pFe at pH ˜10.6. Tc K-edge XANES and EXAFS analyses indicated that the removed Tc species was 70-80% Tc(IV) that was likely incorporated into Fe corrosion products (i.e., Fe(OOH), Fe3O4) and 20-30% unreduced TcO4-. In contrast, the removed Re species was ReO4- only, without detectable Re(IV). In addition, the sequestered ReO4- was not extracted (

We report the first example of linker modification for an N-donor Ag-based cationic material while maintaining and in some cases increasing the anion exchange capacity. Cationic silver(I) pyrazine nitrate selectively traps harmful oxo-anions from water such as permanganate, perrhenate and a variety of α,ω-alkanedicarboxylates. We chose these anions as initial examples of exchange for potential water purification. The host-guest interaction between the cationic layers of π-stacked silver pyrazine polymers and the incoming/outgoing interlamellar anions allows for the exchange. The exchange capacity over 24 h reached 435 and 818 mg/g for permanganate and perrhenate, respectively, a record for a crystalline metal-organic material and over five times the exchange capacity compared to commercial resin. The material also undergoes organic exchange as an analog for pharmaceutical waste, some of which have a carboxylate functionality at the neutral pH range typical of natural water sources. Both the as-synthesized and exchanged materials are characterized by a variety of analytical techniques.

A novel (CuII/ReVII)-heterobimetallic complex based on l -Arginine, namely trans-[Cu( l -Arg)2(ReO4)2] (CuLARe), was successfully synthesized and fully characterized using X-ray structure analysis as well as (IR/UV–vis) spectroscopy, molar conductivity and (TG/DTA) thermal methods. The crystal structure determination reveals that CuLARe has a non-symmetrical atomic arrangement and features striking helical chains of {[Cu( l -Arg)2(ReO4)2]}n, which are further assembled into a 3D-supramolecular network through multidirectional N(C, O)-H⋯O hydrogen bonding interactions. Analysis by Hirshfeld surface generation in combination with 2D-fingerprinting was also performed to elucidate the nature of the interactions and their contributions towards the crystal packing. Moreover, a comparative antioxidant screening of CuLARe with the free ligands as well as CuCl2 has been investigated. The results emphasize that the complexation of ligands to the metal ions plays a crucial role in the improvement of the biochemical properties of CuLARe.

The standard (p° = 0.1 MPa) molar enthalpies of sublimation, at 298.15 K, of methyltrioxorhenium(VII), Δ sub H m o [CH3ReO3] = 70.2 ± 0.4 kJ mol−1, and dirhenium decacarbonyl, Δ sub H m o [Re2(CO)10] = 97.4 ± 0.9 kJ mol−1, corresponding to well characterized crystalline phases, were determined by Calvet microcalorimetry. These results, along with structural information obtained in this work by single crystal X-ray diffraction for CH3ReO3, or previously reported for Re2(CO)10, tetramethylammonium perrhenate(VII), [N1111][ReO4], and hexamethylrhenium(VI), Re(CH3)6, were used to extend our previously developed all-atom force field for organometallic compounds, to rhenium species. The new parametrization was able to reproduce the enthalpies of sublimation and unit cell parameters of the test set with maximum absolute deviations of 3.3 kJ⋅mol−1 and

Oxorhenium catalysts effectively transform biomass-derived polyols into corresponding alkenes via deoxydehydration (DODH) with a secondary alcohol as a hydrogen donor. This study describes the preparation of unsupported rhenium oxide nanoparticles (ReOx NPs), their use as DODH heterogeneous catalyst, and changes in the speciation and structure of Re during catalysis leading to a possible mechanism for DODH by a heterogeneous catalyst. The unsupported nanoparticles catalyze various polyols transformation to produce alkenes with high efficiency and recyclability. X-ray spectroscopy analysis shows that the structure of as-prepared ReOx NPs is similar to perrhenate with oxidation state between Re(VI) and Re(VII). Under reaction conditions and postcatalysis, the ReOx NPs are reduced by approximately two oxidation units. Kinetic isotope effect demonstrates that dissociation of a C–H bond during reduction of ReOx NPs by 3-octanol is part of the rate-determining step. Based on all experimental observations, the m...

Heat capacity for 1-hexyl-3-methyl imidazolium perrhenate ionic liquid [C6MIM][ReO4] in the temperature range from 79 to 396 K has been measured by a fully automated adiabatic calorimeter. For [C6MIM][ReO4], glass transition temperature, the melting temperature, standard molar heat capacity, enthalpy and entropy of solid–liquid phase transition were determined to be (202.164 ± 0.405) K, (226.198 ± 0.265) K, (480.702 ± 0.013) J K−1 mol−1, (15.665 ± 0.195) kJ mol−1 and (69.250 ± 0.780) J K−1 mol−1, respectively. In addition, the thermodynamic characteristics and solid–liquid phase change behavior of [C6MIM][ReO4] were compared with the ones of [C7MIM][ReO4] reported in the literature. The thermodynamic functions (HT− H298.15), (ST− S298.15) and (GT− G298.15), for the compound in the experimental temperature range were calculated.

The ionic liquid 1-(2-methoxyethyl)-3-ethyl imidazolium perrhenate [C22O1IM][ReO4] was prepared in the laboratory firstly, and its structure was confirmed by 1H NMR and 13C NMR. The heat capacities were precisely measured in the temperature range from 78 to 392 K by means of a fully automated adiabatic calorimeter. For [C22O1IM][ReO4], the melting temperature, standard molar heat capacity, molar enthalpy, and molar entropy of solid–liquid phase transition were determined to be (211.826 ± 0.130) K, (142.31 ± 0.34) J K−1 mol−1, (14.382 ± 0.046) kJ mol−1, and (67.93 ± 0.22) J K−1 mol−1, respectively. And the experimental values of molar heat capacities were fitted to a polynomial equation using least square method in the appropriate temperature ranges. The thermodynamic functions (HT − H298.15) and (ST − S298.15) were also obtained from the heat capacity data in the experimental temperature range with an interval of 5 K.

Rhenium and molybdenum are valuable metals present in the earth's crust in very low concentration and are increasingly used in industry thanks to their multiple properties, but due to the harmful aspects of the production process, there is a need to develop systems of concentration or purification of salts of these elements. For this work a PEG/Na2MoO4 aqueous two phase system (ATPS) was used for the partition of ReO4- anion. By using a central composite design, the effects of PEG concentration, sodium molybdate concentration, temperature, pH and their possible interaction on the partition coefficient were studied, also to estimate the optimal configuration of the factors that influence the process. At the same time, experimental density, sound velocity and isentropic compressibility were also obtained for top and bottom phases. The results showed that the optimal conditions for the partition of ReO4− anion using the ATPS formed by PEG and Na2MoO4 were 14.7 wt% PEG 4000, 16.3 wt% Na2MoO4, 35 °C and pH 6. For these conditions, the partition coefficient (K) obtained was up to 17.8 ± 0.78. The order of factors with high significance on the partition coefficient was: Na2MoO4 concentration > PEG concentration > temperature > pH > interaction between Na2MoO4 and PEG concentrations; the effect of these parameters mainly is related with the speciation, salting-out effect and hydrophobicity. The influence of these factors on the density, and sound velocity of the top phase was minimal, unlike its influence on the properties of the bottom phase, not isentropic compressibility and effect of PEG and Na2MoO4 concentrations on sound velocity. The evaluation of the partitioning behavior was made by experimental design, applying statistical regression analysis and analysis of variance (ANOVA). The statistical models for partition coefficient and for phase densities (and the other properties) as function of parameters with significant effects were obtained, and also a good correlation between experimental and correlated data was observed (R-Squared = 0.9379, ReO4− partition coefficient; 0.9882, bottom phase; and 0.9836 upper phase). This work is oriented to the possible application in stripping of a top phase provided for a co-extraction of rhenium and molybdenum by ATPS in acidic media or in solutions with high contend of Mo such as those provided by pressure oxidative leaching of molybdenite in basic media.

Актуальность. Рений и его сплавы являются тугоплавкими, жаропрочными, жаростойкими и коррозионностойкими материалами, которые используются в авиа- и ракетостроении, электротехнике, при производстве катализаторов. Рений относится к редким и рассеянным элементам, что обусловливает необходимость совершенствования технологических процессов по его извлечению из природного сырья и отработанных материалов, а также повышения точности аналитических методик его определения. Электрохимические методы являются оптимальными с точки зрения затратности, экспрессности и доступности для анализа и переработки ренийсодержащего сырья. В связи с этим изучение закономерностей протекания электродных процессов с участием рения и его соединений является актуальным. Цель: установить последовательность протекания катодного восстановления перренат-ионов в щелочных электролитах. Объекты: растворы перрената аммония, растворы гидроксида натрия. Методы: постоянно- и переменнотоковая полярография, циклическая вольтамперометрия, накопительный потенциостатический электролиз. Результаты. Определён интервал потенциалов катодного восстановления ионов ReO4- (1*10-5…1*10-2 М) в щелочной среде (1…10 М NaOH) на ртутных электродах, составляющий -1,25…-1,75 В (нас. х.с.э.). По результатам определения температурной зависимости величины предельного тока восстановления и зависимости тока от высоты столба капающего электрода установлен существенный вклад каталитической и адсорбционной составляющих в суммарное значение катодного тока. С использованием циклической вольтамперометрии установлена последовательность и предложена схема восстановления ReO4- в щелочных электролитах, включающая электродные, химические и адсорбционные стадии. При интерпретации результатов использованы данные по потенциостатическому электролизу и вольтамперометрии химически синтезированного оксида ReO2. Показана важность учёта полученных результатов при определении рения с использованием электрохимических методов анализа. Relevance. Rhenium and its alloys are refractory, heat-resistant, high-temperature, and corrosion-resistant materials which are used in aircraft and rocket engineering, electrical engineering, in production of catalysts. Rhenium belongs to rare elements, this necessitates the improvement of technological processes for its extraction from natural raw materials and waste materials, as well as improving the accuracy of analytical methods for its determination. Electrochemical methods are optimal in terms of cost, expressiveness and availability for analysis and processing of rhenium-containing raw materials. In this regard, the study of the regularities of the electrode processes involving rhenium and its compounds is relevant. The aim of the research is to establish the sequence of cathodic reduction of perrhenate ions in alkaline electrolytes. Objects: ammonium perrhenate solutions, sodium hydroxide solutions. Methods: direct and alternating current polarography, cyclic voltammetry, accumulative potentiostatic electrolysis. Results. The authors have determined the interval of potentials of cathodic reduction of ReO4 - ions (1*10-5…1*10-2М) in alkaline medium (1...10 M NaOH) at mercury electrodes is -1,25…-1,75 V (sat. Ag/AgCl/KCl). A significant contribution of catalytic and adsorption current components to the total value of cathodic current was established on the basis of temperature dependence of limiting current and current dependence on height of dropping Hg-electrode column. A sequence for reduction of ReO4 - in alkaline electrolytes was established using cyclic voltammetry, and a scheme of the cathodic process was proposed which includes electrode, chemical and adsorption stages. Experimental data on potentiostatic electrolysis and on voltammetry of chemically synthesized ReO2 were used to interpret the polarographic results. The paper demonstrates the importance of the obtained results for analytical determination of rhenium.

Environmental contamination by 99Tc(VII) from radioactive wastewater streams is of particular concern due to the long half-life of 99Tc and high mobility of pertechnetate. Herein, we report a novel MXene-polyelectrolyte nanocomposite with three-dimensional networks for enhanced removal of perrhenate, which is pertechnetate simulant. The introduction of poly(diallyldimethylammonium chloride) (PDDA) regulates the surface charge and improves the stability of Ti2CT x nanosheet, resulting in Re(VII) removal capacity of up to 363 mg g-1, and fast sorption kinetics. The Ti2CT x/PDDA nanocomposite furthermore exhibits good selectivity for ReO4- when competing anions (such as Cl- and SO42-) coexist at a concentration of 1800 times. The immobilization mechanism was confirmed as a sorption-reduction process by batch sorption experiments and X-ray photoelectron spectroscopy. The pH-dependent reducing activity of Ti2CT x/PDDA nanocomposite toward Re(VII) was clarified by X-ray absorption spectroscopy. As the pH increases, the local environment gradually changes from octahedral-coordinated Re(IV) to tetrahedral-coordinated Re(VII). The overall results suggest that Ti2CT x/PDDA nanocomposite may be a promising candidate for efficient elimination of Tc contamination. The reported surface modification strategy might result in applications of MXene-based materials in environmental remediation of other oxidized anion pollutants.

A comparative study of the sorption properties of N-(2-carboxyethyl)chitosan (CEC), N-(2-sulfoethyl)chitosan (SEC), N-(2,3-dihydroxy)propyl chitosan (HPC) and N-2-(2-pyridyl)ethyl chitosan (PEC) with respect to perrhenate ions in an acidic medium was carried out. On the basis of the analysis of the adsorption isotherms and the perrhenate ion adsorption degrees as functions of pH, it was found that the efficiency of adsorbents decreases in the sequence PEC > SEC > HPC > CEC. The investigated chitosan derivatives are characterized by a higher rate of sorption of perrhenate ions in comparison with known commercial anionites. In the case of PEC, accompanying ions have the least effect on the sorption.

The effect of Bacillus spp. on Re(VII) and Se(IV) diffusion in compacted GMZ bentonite was investigated by a through-diffusion method. Bacillus spp. had no significance effect on the effective diffusion coefficient (De) and the accessible porosity (eacc) of Re(VII), whereas a decrease of De and an increase of distribution coefficient (Kd) were observed for Se(IV). Moreover, Archie’s law and an exponential decay equation were employed to fit the De value of Re(VII) and Se(IV).

The methods of stationary voltammetry and chronovoltammetry have been used to study deposition processes of ternary CoWRe alloys at different rhenium content of the electrolyte and deposition current density. It has been found that the limiting currents have a diffusive nature and are proportional to the concentration of perrhenate ions in the electrolyte. The CoWRe alloys should be formed by the discharge of bimetallic citrate complexes of the following composition [(Co)(WO4)(H)(Cit)]2- and rhenium electrodeposition. Rhenium does not form complexes with citrate ions and deposits better in an alloy with iron group metals than in the form of an individual metal from a perrhenate solution. It can be assumed that the discharge of rhenium into the alloy occurs from a surface complex, the nature of which has not yet been established. The alloy current efficiency reaches 93% due to the high overpotential of hydrogen evolution on the alloy surface. According to the results of investigations of the catalytic properties of alloys in the hydrogen reduction reaction, it has been found that with increasing the rhenium content of the electrolyte and alloy, an increase in hydrogen overpotential is observed. Based on the Tafel coefficients found, it was found that in an acidic and neutral medium, the limiting stage of the cathodic and anodic reaction is the transfer of the first electron. In an alkaline medium, the anode process is complicated by the simultaneous transport of two electrons. The found values of corrosion resistance are 1-2 kOm·cm-2 in solutions of 0.01 M H2SO4; 20-110 kOm·cm-2 in 2.5% NaCl; 10-30 kOm·cm-2 in 1.0 M KOH. Based on the dependence of corrosion resistance on the refractory metals content of the alloy and the electrodeposition conditions, the optimum deposition current density of 10 mA·cm-2 has been found.

A family of pyridyl-functionalized arylacetylene C–H hydrogen bonding (HB) receptors were synthesized and binding interactions to perrhenate (ReO4–) studied in the solid state. The protonation and alkylation state of the pyridine nitrogen dictate the location and denticity of the interactions. X-ray structures of neutral 1 and singly charged 2a+·ReO4– reveal the formation of favorable self-complementary dimers, owing to the presence of nitrogen HB acceptor sites. Dismissal of these dimers upon elimination of nitrogen HB acceptors on the receptor result in an array of multidentate C–H HB receptor–guest contacts.

The recovery of scattered metal ions such as perrhenate (Re(VII)) from industrial effluents has enormous economic benefits and promotes resource reuse. Nanoscale-metal/biochar hybrid biosorbents are attractive for recovery but are limited by their insufficient stability and low selectivity in harsh environments. Herein, a superstable biochar-based biosorbent composed of ZnO nanoparticles with remarkable superhydrophobic features is fabricated, and its adsorption/desorption capabilities toward Re(VII) in strongly acidic aqueous solutions are investigated. The ZnO nanoparticle/biochar hybrid composite (ZBC) exhibits strong acid resistance and high chemical stability, which are attributable to strong C-O-Zn interactions between the biochar and ZnO nanoparticles. Due to the advantages of its hydrolytic stability, superhydrophobicity, and abundance of Zn-O sites, the ZBC proves suitable for the effective and selective separation of Re(VII) from single, binary and multiple ion systems (pH = 1), with a maximum sorption capacity of 29.41 mg/g. More importantly, this material also shows good recyclability and reusability, with high adsorption efficiency after six adsorption-desorption cycles. The findings in this work demonstrate that a metal/biochar hybrid composite is a promising sorbent for Re(VII) separation.