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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.

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.

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.

Receptors bearing hydrogen and halogen bond donors for recognition of perrhenate and pertechnetate were designed and studied. Acyclic hosts with N-H and C-H binding sites showed the best selectivity for TcO4- and ReO4- over spherical and more basic tetrahedral anions.

Alpha-cyclodextrin based anion receptors functionalised with pendant arms containing halogen and hydrogen bond donor motifs display selective association of perrhenate in aqueous media at neutral pH. NMR and ITC anion binding investigations reveal the halogen bonding receptor to be the superior host.

Lanthanum perrhenate for use as a lubricating additive was prepared via the aqueous solution method in this study, and was dispersed into a pentaerythritol ester (PETE) base oil accompanied by surface active agents. The thermal stability of the complex oil with/without lanthanum perrhenate and surface active agents was evaluated by thermogravimetry. The influences of lanthanum perrhenate as a solid lubricating additive on the extreme pressure performance and friction-reducing property of the complex lubricants in a wide temperature range were investigated by four-ball tests and ball-on-disc frictional tests with a silicon nitride ball and Ni-base superalloy frictional pair. The results suggested that the added lanthanum perrhenate did not significantly affect the thermal stability and anti-oxidation properties of PETE, and improved the extreme pressure performance of the base oil. Additionally, it decreased the friction coefficient and wear scar diameter to a certain degree. The complex oil had a similar lubricating performance to the base oil below the decomposition temperature point; within the scope of 350 °C to 600 °C, the friction coefficients of oil containing the lanthanum perrhenate additive were markedly lower than that of the base oil, and this was attributed to lanthanum perrhenate's intrinsic shear susceptibility and resistance to phase transformation under high temperature conditions, enabling it to form an effective antifriction layer with native oxides of the superalloy matrix, thus reducing the friction in high-temperature environments.

Low-symmetry metal–organic architectures that feature unusual binding motifs are useful for exploring new modes of guest recognition. Such structures remain difficult to create using current rational design principles. One approach to constructing such architectures is to employ ligands with coordination vectors oriented to preclude the formation of simple, low nuclearity molecular assemblies upon complexation to metal ions. Here we report two new supramolecular assemblies generated from such a ligand: a simple metastable [Zn3L3]6+ assembly, which was observed to convert to a more complex [Zn9L5(μ-OH)6]12+ twisted half-pipe architecture. Two chemically distinct stimuli—an anionic template and a base—must be applied for the conversion to occur. Perchlorate, perrhenate, trifluoromethanesulfonate and 2-naphthalenesulfonate were found to act as competent templates for the [Zn9L5(μ-OH)6]12+ structure.

A new imidazolium-based polymeric ionic liquid (PC2vimBr) gel was prepared by γ-radiation induced polymerization and crosslinking of 1-vinyl-3-ethylimidazolium bromide and a functional crosslinker 3,3′-divinyl-1,1′(1,6-hexanediyl) diimidazolium dibromide. A high gel fraction of ca. 95% could be achieved under 40 kGy, and the equilibrium degree of swelling and mechanical properties could be adjusted by crosslinker content and absorbed dose. The highest fracture compressive strength of PC2vimBr could be as high as 0.21 MPa. PC2vimBr could strongly adsorb perrhenate (ReO4−) with an adsorption capacity as high as ca. 8.6 × 102 mg g−1 (Re/gel), following a Langmuir model by an ion exchange mechanism, which was confirmed by IR and XPS. Competitive adsorption with the electrolytes or sodium dodecyl benzene sulfonate showed that the PC2vimBr gel has good efficiency for ReO4− removal from a low concentration of electrolyte solution or laundry waste water. Considering ReO4− is the natural analogue of TcO4−, PC2vimBr may be used in decontamination of low level wastes such as laundry wastes. Interestingly, PC2vimBr would shrink strongly after adsorbing ReO4−, which is meaningful for volume reduction of radioactive wastes.

A novel strong-base anion exchanger (PS-g-4VP-IE) is prepared by γ-irradiation-induced grafting of 4-vinyl pyridine onto polystyrene microspheres, followed by a quaternization process. The effects of absorbed dose and monomer concentration on grafting yield and quaternization time on conversion ratio were investigated in order to obtain optimum synthesis conditions. The FTIR and XPS results effectively manifest the successful synthesis of PS-g-4VP-IE. Furthermore, the effect of solution acidity on adsorption efficiency, adsorption kinetics and adsorption isotherm were investigated in batch-wise experiments. The results reveal that the adsorption towards perrhenate (ReO4−) not only has rather fast adsorption kinetics, but also matches well with the Langmuir isotherm model. Thus, its theoretical maximum adsorption capacity is deduced to be 252 mg g−1, while that of the couterpart is 247 mg g−1 in column experiments. The concentrated elution peak shows the potential application of PS-g-4VP-IE in concentrating ReO4−.

The adsorption of perrhenate ions by the bio-char prepared from Acidosasa edulis shoot shell at 773 K is investigated under acidic conditions. The effects of some important parameters including initial pH (1.0–6.0), adsorbent dose (0.8–8.0 g L−1), contact time (2–480 min) and initial perrhenate ion concentration (10–100 mg L−1), on the recovery of perrhenate ions from aqueous solution in batch experiments are tested. The adsorbent was characterized by scanning electron microscopy equipped with an energy-dispersive X-ray spectroscopy (SEM-EDX), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and specific surface area analysis. The adsorption data are well described by Freundlich isotherm and maximum perrhenate ions adsorption capacities of 14.6 mg g−1 for Acidosasa edulis shoot shell bio-char under the optimum conditions. Kinetics of adsorption are found to follow the pseudo-second-order rate equation. Thermodynamic analysis suggested that the adsorption is an endothermic process and occurs spontaneously. FTIR analysis confirmed the major involvement of hydroxyl and carboxyl groups during perrhenate ion adsorption. Further, more than 94% of total rhenium adsorbed could be recovered using 0.1 mol L−1 KOH as a desorption medium. The mechanism analysis indicates that the outer-sphere complexes and electronic attraction mechanism were involved in the adsorption of perrhenate ions. The results indicate that Acidosasa edulis shoot shell waste derived bio-char can act as an effective adsorbent material for perrhenate ions recovery from copper smelting acidic wastewater.

Organic-phase supramolecular ion pair (SIP) host-guest assemblies of perrhenate anions (ReO4(-)) with ammonium amide receptor cations are reported. These compounds act as catalysts for the epoxidation of alkenes by aqueous hydrogen peroxide under biphasic conditions and can be recycled several times with no loss in activity.

A series of imidazolium perrhenates with different substituents at the imidazolium ring were synthesised and characterised, including single crystal X-ray diffraction. The effect of the substitution pattern on the state of aggregation of the compounds, the charge delocalisation and the ion pairing interaction via hydrogen bonds was studied. Particularly the substitution at the C2 position of the imidazolium ring was shown to be crucial to fine-tune the ion contacts. Fluorinated substituents appear to exhibit enhanced interionic interactions. The ability to tune the degree of contacts of the perrhenate anion allows for adjusting the nucleophilicity of this anion.

(1)H NMR spectroscopic and X-ray crystallographic investigations of a 1,3-bis(4-ethynyl-3-iodopyridinium)benzene scaffold with perrhenate reveal strong halogen bonding in solution, and bidentate association in the solid state. A nearly isostructural host molecule demonstrates significant C-H hydrogen bonding to perrhenate in the same phases.

Recently it was shown that water and air stable perrhenate based ionic liquids (ILs) are promising catalysts for oxidation reactions. For a broader application and in the context of green chemistry it is important to study in addition to their technical performance also their potential impact on environment and human health. This paper presents the first account on (eco)toxicological and biodegradation data for a set of ammonium and imidazolium based ILs with perrhenate anions.

The reaction of the oxidorhenium(V) precursor [ReOCl(3)(PPh(3))(2)] with the proteinogenic amino acid L-histidine (L-hisH) and the glycosides methyl alpha-D-mannopyranoside (Me-alpha-D-Manp) and methyl beta-D-ribopyranoside (Me-beta-D-Ribp) in methanol/triethylamine yielded the crystalline compounds [ReO(L-his)(Me-alpha-D-Manp2,3H(-2))] x 2MeOH (1) and [ReO(L-his)(Me-beta-D-Ribp3,4H(-2))] x (1/2)MeOH (2). The mixed-ligand complexes based on the Re(V)O moiety were characterised by single-crystal X-ray diffraction, NMR spectroscopy, elemental analysis and mass spectrometry. Both complexes are hydrolytically stable over prolonged periods of time and are accessible also by a purely aqueous route by replacing the rhenium(V) precursor with a perrhenate/reductant couple.

Avoiding the use of toxic methyltin precursors to synthesize methyltrioxorhenium (MTO) and its mono- and bis-peroxo derivatives, applicable as oxidation catalysts, dimethyl zinc might be considered a promising alternative alkylating agent. However, the methylrhenium(VI) dimers, formed as reduction products alongside MTO during the reaction of dimethyl zinc with Re2O7, are not as straightforwardly transformed into the epoxidation catalysts as MTO itself in the presence of excess H2O2. In the case of red (μ-oxo)bis[trimethyloxorhenium(VI)], the main reaction product with H2O2 is the catalytically inactive trimethyldioxorhenium(VII). In the case of bis[dimethyl(μ-oxo)oxorhenium(VI)], slow conversion to the monomeric mono- and bis-peroxo congenes of MTO occurs. Furthermore, part of the Re(VI) starting complex is transformed into inactive perrhenate. While bis[dimethyl(μ-oxo)oxorhenium(VI)] might be applied (also in a mixture with MTO) as an oxidation catalyst precursor, (μ-oxo)bis[trimethyloxorhenium(VI)] can be applied as a useful precursor for the synthesis of trimethyldioxorhenium(VII), which was previously only accessible by less convenient synthetic pathways.

The first structural characterization of an actinide complex with coordinated perrhenate is reported, [UO2(ReO4)2(TPPO)3] (1). In this {UO2}2+ complex two [ReO4]− anions and three TPPO (triphenylphosphine oxide) PO donor ligands are coordinated in the equatorial plane in a cisoid arrangement. This bonding arrangement, and apparent strain observed in the equatorially bonded ligands, is attributed to the solid state packing in adjacent molecules in which hydrophobic TPPO ligands form an effective “shell” around a hydrophilic core of two UO2(ReO4)2 moieties. Solid state vibrational spectroscopy (infrared and Raman), 31P CP MAS NMR and elemental analysis are also consistent with the formula of 1. Solution state vibrational spectroscopy and 31P NMR measurements in EtOH indicate the lability of the TPPO and [ReO4]− groups. The photolytic generation of peroxide in EtOH solutions of 1 leads to the formation of trace quantities of [{(UO2)(TPPO)3}2(µ2-O2)][ReO4]2, 2, in which the coordinated [ReO4]− groups of 1 have been displaced by bridging O22−, derived from atmospheric O2. Finally, attempts to synthesise a {NpO2}+ analogue of 1 have resulted only in the formation of [NpO2(TPPO)4][ReO4], 3, in which [ReO4]− acts solely as a counter anion. From these results it can be concluded that [ReO4]− will bond to {UO2}2+, but will be readily displaced by a more strongly coordinating ligand (e.g. peroxide) and will not coordinate to an actinyl cation with a lower charge, {NpO2}+, under the same reaction conditions.

The development of the rhenium-188 generator has provided a convenient and economic source of radionuclide for targeted radionuclide therapy of cancer. To exploit this more widely, mild, convenient and efficient methods for stable incorporation of the radionuclide into biomolecules are required. The aim of this work is to exploit the tumour targeting therapeutic radiopharmaceutical [ReO(dmsa)2]− (H2dmsa = meso-dimercaptosuccinic acid), which is easily synthesised in radioactive form and highly stable in vivo, for this purpose. A new efficient synthesis of [ReO(dmsa)2]−, as a single isomer (syn-endo), from perrhenate using acetylhydrazine as reductant, is reported. Dehydration of the two dicarboxylic acid groups of [ReO(dmsa)2]− with dicyclohexylcarbodiimide gives the yellow cyclic dianhydride [ReO(dmsaa)2]− (H2dmsaa = meso-dimercaptosuccinic anhydride) without disrupting the ReOS4 core. As its tetraethylammonium salt, [ReO(dmsaa)2]− was characterised crystallographically as a distorted square pyramidal complex with an axial oxo-group and a syn-endo orientation of the two anhydride rings with respect to this oxo-group. [ReO(dmsaa)2]− reacts with primary and secondary amines including lysine residues of peptides, to form amide-linked conjugates, which were identified by ES-MS. The syntheses are fast, efficient and employ mild conditions, making them readily adaptable for a kit-based approach to rhenium and technetium radiopharmaceuticals.

Three completely different salts, (BET-TTF)ReO4 (1), (BET-TTF)3(ReO4)2 (2), and (BET-TTF)9(ReO4)4·2(THF) (3) are obtained by small variations in the electrocrystallization conditions of bis(ethylenethio)tetrathiafulvalene (BET-TTF) with the ReO4− ion. The crystal structures of the three salts show strong differences between them. In salt 1, the completely ionic BET-TTF stacks, running along the a direction, are not regular but are forming weak dimers. Two different radical cation layers configure salt 2 and the analysis of the bond-length of BET-TTF molecules forming layers 1 and 2 shows that the β-like layer 1 has mixed valence character, while layer 2 can be regarded as an anion-cation-anion [ReO4(BET-TTF)ReO4]− sandwich layer with completely ionised BET-TTF. Only one β-like layer that consists of two different mixed valence stacks forms salt 3. Conductivity measurements show that mixed valence salts 2 and 3 are metals with a metal-semiconductor transition around 125 K and 75 K respectively whereas the completely ionised salt 1 is, as expected, a semiconductor. The effect of high quasi-hydrostatic pressure and magnetic field on the transport properties of salt 3 has also been studied. The relationship between the crystal structure and the transport properties of all three salts has been analysed by means of tight binding band structure calculations. These calculations show that layer 1 is responsible for metallic conductivity of salt 2 whereas in layer 2 the electrons are localised. EPR data of this salt indicate that there is an appreciable interaction between delocalised electrons in layer 1 and localised magnetic moments in layer 2.

Removal of a CO ligand from the η1-benzyl complex [Re(CO)2(η1-CH2Ph){NH(Me)CH2CH2(η5-C5H4)}]+Br– yielded an η3-benzyl complex. The η3 co-ordination mode was converted into η1 when the compound was dissolved in acetonitrile. Evaporation of acetonitrile removed the labile acetonitrile ligand and regenerated the η3-benzyl complex. The η3-benzyl complex [Re(CO)(η3-CH2Ph){NH(Me)CH2CH2(η5-C5H5)}]+BF4– is stable to air and moisture. The corresponding perrhenate salt has been characterized crystallographically. The tetrafluoroborate reacted with bromide, chloride and acetate anion to give the corresponding neutral η1-benzyl complexes in excellent yield. When treated with two-electron donor ligands, such as tert-butyl isocyanide and pyridine, it was converted into the corresponding (η1-benzyl)(isocyanide) and pyridine complexes.

Rate constants (25 °C) have been determined for the oxidation of the ReIV2 complex di-µ-oxo-bis[dioxalatorhenate(IV)], [(C2O4)2Re(µ-O)2Re(C2O4)2]4–, I= 1.00 M (ClO4– or Cl–). Whereas the complex is itself stable in air at pH 7 over many days, at lower pH there is a slow decay of the 446 nm peak (Iµ= 6840 M–1 cm–1 per ReIV2) to give in air the colourless perrhenate(VII)[ReO4]– product, peak at 225 nm (Iµ= 3400 M–1 cm–1). The kinetics indicate a protonation step, equilibrium constant K= 2.4 M–1, followed by the decay process k= 4.3 × 10–5 s–1. With the one-equivalent oxidants cis-[VO2(H2O)4]+(1.0 V) and [Mo(CN)8]3–(0.80 V), stoichiometries of 6 mol of oxidant per ReIV2 are obtained indicating conversion through to ReVII. Two kinetic stages have been monitored with the oxidant in large excess. For the reaction with VV as oxidant the first stage is dependent on [VV] and [H+] as well as [ReIV2], giving the rate constant k1= 3.31 × 104 M–2 s–1. Since in the corresponding reaction with MoV as oxidant the reaction is independent of [H+](kMo= 2.27 × 104 M–1 s–1), it is concluded that the VV reactant introduces the [H+]-dependent term. The second stage of the VV reaction gives the rate law dependence k2obs=k2[VV]+k0, but with the less strong Mo oxidant k2obs=k0 which is ≈0.20 s–1. The spectrum of the ReIVReV intermediate, peak at 529 nm (Iµ= 3800 M–1 cm–1), was obtained by stopped-flow rapid-scan spectrophotometry. Reactions of less than full stoichiometric amounts of VV with ReIV2, followed by QAE-Sephadex chromatography at 0 °C, gave orange-pink (peak at ≈495 nm) and maroon (≈550 nm) intermediates, which undergo spontaneous decay.

Reaction of the ReIII bis-diazenido starting materials [ReCl(NNC6H4X-4)2(PPh3)2](X = Cl 1 or Me 2) with excess dppe (Ph2PCH2CH2PPh2) in methanol–toluene under reflux gave the novel orange-brown, formally 20-electron ReIII bis-diazenido cations [Re(NNC6H4X-4)2(dppe)2]+(X = Cl or Me) in good yield by addition of a suitable anion to the cooled reaction mixture. Reaction of 1 and 2 with the more reducing dmpe (Me2PCH2CH2PMe2) ligand gave the formally 20-electron bis-diazenido cation [Re(NNC6H4X-4)2(dmpe)2]+ for X = Cl but the 18-electron mono-diazenido cation [ReCl(NNC6H4X-4)(dmpe)2]+ for X = Me. The structures of complexes [Re(NNC6H4Me-4)2(dppe)2][PF6]·2dmf (dmf = dimethylformamide)5, [Re(NNC6H4Cl-4)2(dmpe)2][PF6]6 and [ReCl(NNC6H4Me-4)(dmpe)2][PF6]7 have been determined: 5, triclinic, space group P, a= 13.046(3), b= 13.250(3), c= 12.233(4)A, α= 110.74(2), β= 95.86(2), γ= 115.83(2)°, Z= 1, R= 0.040; 6 monoclinic, space group P21/c, a= 8.992(2), b= 21.947(2), c= 18.982(2)A, β= 91.45(1)°, Z= 4, R= 0.056; 7 orthorhombic, space group Pnma, a= 19.298(2), b= 11.327(2), c= 13.960(2)A, α=β=γ= 90°, Z= 4, R= 0.042. All three complexes have pseudo-octahedral co-ordination with four P donors in a planar equatorial array. The M–N–N angle of the diazenide ligands is found to be dependent on the steric requirements of the diphosphine ligands, the smaller dmpe ligand permitting the M–N–N angles in 6 to decrease to 147.3(5) and 149.0(4)° compared to values of around 162.7(2)° for the dppe complex 5. Reaction of [NH4][ReO4] with the arylhydrazine hydrochloride 4-MeC6H4NHNH2·HCl in CH2Cl2 in the presence of SiMe3Cl and pyridine (py) gave the new hydrazide [ReCl3{NN(SiMe3)C6H4Me-4}2(py)]. Subsequent reaction with PPh3 in MeOH gave the ReIII diazenide [Re(OMe)(NNC6H4Me-4)2(PPh3)2], and overall this provides a route for the synthesis of Re diazenides directly from perrhenate.

The separation performance of inorganic anions ReO4(-), Br(-), SO4(2-), and NO3(-) using porphyrin-alkaloid quaternary salt transporters is examined using parallel artificial membrane permeability assay. Active and selective transport of perrhenate is achieved by porphyrin-brucine conjugates. Herein, chlorides are used as antiporters and complete removal of perrhenates from a source solution is stimulated due to electrostatic effects.

New solid-phases for the binding, separation and extraction of perrhenate and pertechnetate (ReO(4)(-) and TcO(4)(-)) from water solutions have been developed from a selective molecular receptor. Host compounds being capable of encapsulating these oxoanions are of great interest. The azacryptand, containing two tripodal tetra-amine subunits covalently linked by p-xylyl spacers, is known to display high affinity for ReO(4)(-) and TcO(4)(-) in water. The syntheses of new solid phases, obtained by fixing the receptor on mesoporous silica MCM-41 and Amberlite CG50 supports, are here described. FT-IR, micro-Raman, elemental analysis (CHN), sorption isotherms, (29)Si MAS NMR, and SEM/EDS were employed for solids characterisation. Promising performances were found for silica derivatives, for which the amount of the receptor fixed on silica ranged from 0.2 to 0.3 mmol g(-1). The perrhenate sorption mechanism was investigated with the aim to select the conditions for application in batch and fixed bed column systems.

The design and synthesis of a neutral macrocyclic host that is capable of perrhenate and pertechnetate recognition is described. The anion affinities and underlying coordination modes were estimated by several experimental and theoretical methods including a new technique--reverse (99)Tc NMR titration.

A new tripodal tris(amido benzo-15-crown-5) ligand L 1 cooperatively binds chloride, iodide and perrhenate anions via co-bound crown ether complexed sodium cations and efficiently extracts and transports the pertechnetate anion from simulated aqueous nuclear waste solutions via cooperative ion-pair binding effects.

Urea-functionalized dendrimers are prepared, which show very efficient phase transfer in particular of the diagnostically relevant anions pertechnetate, perrhenate and ATP. The extractability rates are evaluated quantitavely by tracer methods. Their pH dependancy allows to steer the release of guest molecules from the dendrimer host.

The reaction between [UO2(ReO4)2.H(2)O] and two equivalents of either tri-n-butyl phosphine oxide (TBPO) or tri-iso-butyl phosphate (TiBP) results in the formation of [UO2(mu2-ReO4)(ReO4)(TBPO)2]2 (1) and [UO2(mu2-ReO4)(ReO4)(TiBP)2]2 (2) respectively. Both complexes crystallise as two structurally similar centrosymmetric dimers, the cores containing two uranyl moieties linked by bridging perrhenates. Two P=O donor ligands and one monodenatate perrhenate complete the pentagonal bipyramidal coordination sphere at each metal centre. Both complexes have also been characterised in the solid state by vibrational and absorption spectroscopy. Solution spectroscopic characterisation indicates that both perrhenate and phosphine oxide (1) or phosphate (2) remain coordinated, although it is not possible to state conclusively that the dimeric species remain intact. A low resolution structural study of a minor product from the reaction that yielded revealed a monomeric complex with only monodentate perrhenate coordination, [UO2(ReO4)2(H2O)(TiBP)2] (2'). These results represent the first structural evidence for the bridging coordination mode of perrhenate on coordination to an actinide and yields further insight into the possible solvent phase pertechnetate complexes that may exist in PUREX process phosphate rich solvent.

Reaction of potassium salts of sterically demanding pyrazolates (pz = bis-3,5-tert-butylpyrazolate, pz′ = bis-3,5-tert-butyl-4-methylpyrazolate) with Re2O7 affords soluble η2-pyrazolate complexes of the type [(η2-pz)ReO3(THF)n] (1: pz, n = 1 and 2: pz′, n = 0). They were characterized by spectroscopic methods and by X-ray crystallography confirming the η2-coordinate ligands. Complex 1 employing the ligand with a proton in the 4-position retains one molecule of THF, whereas the additional methyl group in 2 leads to the base-free compound 2. Compound 1 reacts with pyridine and 3,5-dimethylpyridine to form Lewis base adducts of the type [(η2-pz)ReO3(L)] (3: L = py; 4: L = 3,5-Me2py). The pronounced sensitivity towards water of these complexes is demonstrated by the reaction of 1 with one equivalent of water forming the corresponding pyrazolium perrhenate [ReO4][pzH2] (5). Its solid state structure shows a hydrogen bonded dimeric assembly. Catalytic activity of 1 is established in oxygen atom transfer-reactions (OAT) from dimethylsulfoxide to triphenylphosphine, and in epoxidations of cyclooctene employing bis(trimethylsilyl) peroxide (BTSP).

Amido-bridged dinuclear cobalt(III) complexes with 1,4,7-triazacyclononane (tacn) were synthesized from [Co(tacn)(O3SCF3)3] by treatment with potassium amide in liquid ammonia at 100 degrees C. Two isomeric triply bridged complexes, [(tacn)Co(mu-NH2)3Co(tacn)]3+ and [(tacn)Co(mu-NH2)2[mu-tacn(-H)]Co(NH3)]3+, were isolated as perchlorates, and the crystal structure of the perrhenate of the latter complex was determined by X-ray diffraction. In this compound a nitrogen atom (deprotonated) from one of the tacn ligands forms a third bridge together with two amido bridges. In 1.0 M (Na,H)ClO4 ([H+] 0.1-1.0 M) the two isomers undergo acid-accelerated amido bridge cleavage, as earlier found for chromium(III) analogues, in spite of the fact that such bridges are co-ordinatively saturated. The triamido-bridged isomer is in this acid medium in equilibrium with [(H2O)(tacn)Co(mu-NH2)2Co(tacn)(NH3)]4+. An isolated perchlorate of this complex appeared to be the salt of the trans-ammineaqua isomer as determined by X-ray diffraction. Equilibration from both sides fits the first-order rate constant dependence k(obs)=6.2(3) x 10(-5)[H+] + 2.1(2) x 10(-5)(s(-1)) at 40 degrees C. Prolonged treatment of the two triply bridged isomers in 1.0 M HClO4 at elevated temperature produces primarily triply bridged dinuclear species where one or two amido bridges have been replaced by hydroxo bridges.

Bis(2,6-di-tert-butyl-4-methylphenoxy)isobutylaluminium reacts with dirhenium heptoxide to give complexes containing aluminium coordinated with perrhenate and 2,6-di-tert-butyl-4-methylphenoxy ligands which are active new catalysts for the metathesis of alkenes.

Electron spin resonance spectra of the [RuO4]– ion {as A[RuO4], where A = NPrn4, N(PPh3)2 or PPh4} in frozen glasses of dichloromethane at ca. 90 K have been recorded; for A = NPrn4, gx= 1.93, gy= 1.98 and gz= 2.06. The spectrum of [RuO4]–(and its electronic spectrum) have been interpreted and compared with those of an alkaline aqueous solution containing ruthenium(VII) species. The ESR spectrum of powdered potassium ruthenate(VI), trans-K2[RuO3(OH)2], at ca. 90 K was also recorded, and the preparation of [PPh4][RuO4]–, a new salt of [RuO4]–, is described.

The interaction of trimethylsilyl perrhenate, ReO3(OSiMe3), or Re2O7, with o-phenylenediamine gives the homoleptic amido complex cation of rhenium(VII), [Re{o-(HN)2C6H4}3]+, as its perrhenate salt. The cation can be reduced by sodium to the neutral rhenium(VI) species Re[o-(HN)2C6H4]3′ which can be reoxidised by AgPF6 to the cation as its hexafluorophosphate salt. Interaction of [Re{o-(HN)2C6H4}3]+ with KOH leads to the singly and doubly deprotonated species, Re[o-(HN)2C6H4]2[o-(HN)NC6H4] and K[Re{o-(HN)2C6H4}{o-(HN)NC6H4}2]. An improved preparation of the known amido thiolate Re[(HN)SC6H4]3′i.e. interaction of o-(H2N)(HS)C6H4 with ReO3-(OSiMe3), is described; the osmium analogue, Os[(HN)SC6H4]3′ is synthesised by interaction of the aminothiol with OsO4. Interaction of OsO4 with o-(H2N)2C6H4 gives the complex trans-OsO2[(HN)2C6H4]2. Infrared, 1H n.m.r., e.s.r., and electronic absorption and cyclic voltammetric data are given. The X-ray crystal structure of the cation [Re{o-(HN)2C6H4}3]+ as the acetone solvate of the perrhenate shows a trigonal prismatic geometry, which is also confirmed for Re[o-(HN)2C6H4]3, Re[o-(HN)2C6H4][o-(HN)NC6H4], K[Re{o-(HN)2C6H4}{o-(HN)NC6H4}2], and Re[(HN)SC6H4]3. The structure of Os[o-(HN)SC6H4]3 shows it to have a slightly distorted octahedral geometry.

The standard enthalpies of formation of ammonium and rubidium perrhenate have been determined, and the difference between them, 132.8 ± 1.5 kJ mol–1 is, as previously predicted, consistent with the observed barrier to ammonium ion rotation of 9–10 kJ mol–1. New thermodynamic properties are proposed for the perrhenate ion, including Sm⊖(ReO4–, aq)= 198.1 ± 3 J K–1 mol–1, and derived values consistent with these are ΔfHm⊖(NH4ReO4, s)=–975 kJ mol–1, ΔfHm⊖(RbReO4, s)=–1 108 kJ mol–1, and Sm⊖(RbReO4, s)= 182 J K–1 mol–1. As with several other anions which provide relatively little resistance to ammonium ion rotation, the solubility of the ammonium salt exceeds that of the rubidium compound. This may be attributable to hydrogen bonding of the ammonium ion in aqueous solution.

The extraction of septivalent rhenium into tributyl phosphate from aqueous nitric acid is investigated as a function of solvent concentration in the organic, and nitric acid concentration in the aqueous phase, the rhenium concentration being kept constant. The method of continuous variations is applied to follow the formation of the extractable rhenium compound. The results revealed that perrhenic acid was the only extractable species. The solvent-dependencies are found to be of the direct fourth-power. The mass- action effect and anti-synergic interation between nitric and perrhenic acid are used to interpret the extraction mechanism involved. An attempt is made to calculate the formation constant of perrhenic acid tetrasolvate. (auth)

The matrix i.r. and Raman spectra obtained from the vaporisation of potassium and caesium perrhenate show spectra characteristic of the molecular species MReO4 with C2v symmetry. Additional 18O enrichment experiments provide an unequivocal assignment for the νRC–O modes and it is also shown that the bond dipole model leads to a useful simulation of relative band intensities.

The reaction of perrhenate with hydroxylammonium chloride (NH3OHCl) has been studied. Hydroxylammonium chloride reacts with rhenium in 8–10 M sodium hydroxide solution to produce a yellow complex which has λmax. at 300 nm with a molar absorptivity of 7.9 × 103 l mol–1 cm–1. The stoicheiometry of the complex has been studied spectrophotometrically using different procedures. A method for the spectrophotometric determination of rhenium has been developed, and this has been applied to the determination of rhenium in molybdenum-rhenium and tungsten-rhenium alloys.

The first homoleptic imido compounds of transition metals, namely the imido analogues of the tungstate, WO42–, and perrhenate, ReO4–, anions have been obtained as the lithium salts, Li2W(NBut)4and Li(tmed)Re(NBut)4; the structure of the tungsten compound contains two W(NBut)4 units linked by N ⋯ Li ⋯ N bridges while that of the rhenium compound shows the lithium co-ordinated to N atoms of tetramethylethylenediamine and to two N atoms of the anion.

The crystal structure of Me3SiOReO3 has been determined by single-crystal X-ray diffraction. The crystals are monoclinic, space group C2/c, with a= 11·34, b= 11·64, c= 13·44 A, β= 99° 58′, and Z= 8. The arrangements about the silicon and rhenium atoms are tetrahedral, with mean Si–C and Re–O bond lengths of 1·92 and 1·63 A; the Re–O–Si angle is 164 ± 5°. The experimental errors in the atomic co-ordinates of the light atoms are large because the rhenium atom dominates the X-ray scattering.

The spectrophotometric methods for determining rhenium and gold with Brilliant green have been re-examined in an investigation of the effects of purity of reagent and acidity on the precision and accuracy of results. The perrhenate-Brilliant green ion-association complex is extracted from a solution at pH 6, and is unaffected by reagent purity. The extraction of the tetrachloroaurate(III)-Brilliant green ion-association complex is carried out from 0·5 M hydrochloric acid solution, however, and an impure reagent gives low recoveries. Procedures are recommended for the determination of rhenium and gold, and the purification of the reagent is discussed.

It is shown from measurements of 1H chemical shifts and integrated Raman intensities of the 972 cm–1 perrhenate band that aqueous perrhenic acid is completely ionized up to 7 mol 1.–1 concentrations.

The polarographic reduction of potassium permanganate, potassium pertechnetate, potassium perrhenate, and potassium octacyanorhenate(V) was studied in aqueous solution with a variety of supporting electrolytes. The polarographic reduction of manganese and rhenium carbonyls, and carbonyl halides was studied in non-aqueous solution, a quaternary ammonium salt being used as supporting electrolyte. The valency states of (+ 6) and (+7) were observed for technetium. A method of purification of the element is described and several analytical procedures are suggested. (auth)

A study has been made of the stability of dilute standard solutions of antimony (4 µg ml–1), arsenic (20 µg ml–1), iron (50 µg ml–1) and rhenium (5 µg ml–1) used in colorimetry. The standard elements in these solutions were determined over a period of 2 months by using colorimetric procedures developed in this laboratory and reported previously. Tests were carried out on standard solutions stored in soda-glass, in borosilicate glass and in rigid polyethylene containers.The dilute standard antimony solutions, prepared either by dissolving antimony potassium tartrate in water, or by dissolving elemental antimony in sulphuric acid and diluting the solution with water, were found to be stable (i.e., to deteriorate by less than 2 per cent.) over a period of 50 days. Similar dilute standard antimony solutions containing hydrochloric acid deteriorated rapidly, however.The dilute standard arsenic solutions prepared either by dissolving arsenic(III) oxide in sodium hydroxide solution and then neutralising the solution with hydrochloric acid, or by dissolving disodium hydrogen arsenate heptahydrate in water, were found to be stable. Arsenic(III) in the former standard solution was oxidised slowly by dissolved oxygen, but the total arsenic present in the solution remained unchanged and could be determined by the molybdenum-blue method.An iron(III) standard solution, 0·06 M in hydrochloric acid and prepared from ammonium iron(III) sulphate, was stable for at least 2 months, as was a standard potassium perrhenate solution in a buffer solution of pH 6.Light in the laboratory and the material of the containers did not adversely affect the solutions reported to be stable. Light accelerated the deterioration of the antimony solutions that contained hydrochloric acid, and the material of the containers had a slight effect on the rate of deterioration.