The substitution of germanium for silicon in AST-type zeolite

The substitution of silicon by germanium in the AST zeolite framework type, [Si_nGe_40−nO₈₀]*4(SDA⁺F⁻) expressed as unit cell content in its cubic F-centered symmetry, has been studied. Three different kinds of templates, dimethyldiethylammonium, dimethyldiisopropylammonium and isopropyltrimethylammonium cations, were used in the hydrothermal synthesis process in fluoride medium. The products were identified with XRD, MAS NMR, SEM and thermal analysis. The analysis of the X-ray powder diagrams shows that AST crystallizes in different space group symmetries depending on the nature of the SDA and the degree of Ge-substitution. The resonance signals of ¹⁹F in MAS NMR experiments for the pure Si- and Ge-end members are at −38.2 and −15 ppm, respectively, indicating that the F⁻-anion is located as co-template in the double-four-ring (D4R) of the tetrahedral framework. This is confirmed by Rietveld analysis of powder diffraction data of the pure Ge-end member. The peak splitting of the ¹⁹F NMR signal in pure GeO₂AST-type material is related to the displacement of F⁻ location inside the D4R. Two more distinct signals at −8 and −19 ppm, respectively, are observed for X-ray pure AST-samples of intermediate compositions and assigned to fluoride in D4R built of 4[GeO₄]- and 4[SiO₄]-tetrahedra (4Ge, 4Si) and to (2Ge, 6Si)-D4R, respectively. An ordered distribution of Ge in the AST-framework is proposed for cubic AST with compositions around Si/Ge=1.5–1 by correlating the intensities of ¹⁹F NMR signals and the results from chemical analysis. This model is further confirmed by the quantitative analyses of the corresponding ²⁹Si MAS NMR spectra.     

Ionic mobility and structure of fluorozirconates Rb2? x (NH4) x ZrF6 ( x > 1.5) by NMR, x-ray structure analysis, and impedance spectroscopy

The ionic mobility in the temperature interval 180 to 480 K, structure, and electrophysical properties of rubidium-ammonium hexafluorozirconates Rb_2−x (NH₄) _x ZrF₆ (1.5 ≤ x ≤ 2.0) are studied by methods of the ¹⁹F, ¹H NMR spectroscopy, x-ray structure analysis, differential thermal analysis, and impedance spectroscopy. Correlations between the composition of the cationic sublattice, the character of ionic motions, and the phase transition temperature (of the type order-disorder) are established in these compounds. The salient feature of the high-temperature modifications of these fluorozirconates with x ≥ 1.5 is the translation diffusion of ions inside the fluoride and ammonium sublattices and the ¹⁹F NMR spectra are characterized by monoaxial anisotropy of the magnetic shielding tensor of the fluorine nuclei. Fluorozirconates with x > 1.5 are shown to belong with the structural type (NH₄)₂ZrF₆. The rubidium cations isomorphically replace the ammonium cations. The electrophysical characteristics of the compounds are examined in the temperature interval 300 to 480 K. It is established that the electroconductivity of these compounds increases with x. Original Russian Text ? V.Ya. Kavun, A.V. Gerasimenko, A.B. Slobodyuk, N.A. Didenko, N.F. Uvarov, V.I. Sergienko, 2007, published in Elektrokhimiya, 2007, Vol. 43, No. 5, pp. 563–570. Based on the paper delivered at the 8th Meeting “Fundamental Problems of Solid-State Ionics”, Chernogolovka (Russia), 2006.     

13C and19F NMR study of α,β-difluorostyryl derivatives of transition metal carbonylates. A method of signal assignment based on the carbon—fluorine spin-spin coupling constants

The¹³C and¹⁹F NMR spectra ofZ- andE-isomers of β-X-substituted α,β-difluorostyrenes (X=F, Cl, CpFe(CO)₂, Re(CO)₅, Re₂(CO)₉Na) were studied. Direct and long-range (across 1–5 bonds) spin-spin coupling constants and the (¹³C−¹²C) isotope shifts in the¹⁹F NMR spectra were determined. The study of the¹³C satellites in the¹⁹F NMR spectra of substituted difluorostyrenes permitted assignment of the¹³C NMR signals of the vinylic carbon atoms. Similarly, the signals in¹⁹F NMR spectra were assigned based on coupling constants of fluorine withipso-carbon. These assignments were found to be in good agreement with the data available from the literature (X=F, Cl). The developed approach was applied to the elucidation of the structure ofZ−PhCF=CClFe(CO)₂Cp. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya. No. 8, pp. 1575–1579, August, 1998.     

Synthesis, vibrational and NMR spectroscopic characterization of [N(CH3)4][IO2F2] and X-ray crystal structure of [N(CH3)4]2[IO2F2][HF2]

The salt, [N(CH₃)₄][IO₂F₂], was prepared from [N(CH₃)₄][IO₃] and 49% aqueous HF, and characterized by Raman, infrared, and ¹⁹F NMR spectroscopy. Crystals of [N(CH₃)₄]₂[IO₂F₂][HF₂] were obtained by reduction of [N(CH₃)₄][cis-IO₂F₄] in the presence of [N(CH₃)₄][F] in CH₃CN solvent and were characterized by Raman spectroscopy and single-crystal X-ray diffraction: C2/m, a = 14.6765(2) Å, b = 8.60490(10) Å, c = 13.9572(2) Å, β = 120.2040(10)°, V = 1523.35(3) Å³, Z = 4 and R = 0.0192 at 210 K. The crystal structure consists of two IO₂⁻F₂ anions that are symmetrically bridged by two H⁻F₂ anions, forming a [F₂O₂I(FHF)₂IO₂F₂]⁴⁻ dimer. The symmetric bridging coordination for the H⁻F₂ anion in this structure represents a new bonding modality for the bifluoride anion.     

Synthesis, characterization and solution behaviour of phosphoryl complexes of tin tetrafluoride

The preparation and characterization of a series of octahedral complexes [SnF₄L₂] (L = (Me₂N)₃PO (1), L = (R₂N)₂P(O)F; R = Me (2); Et (3) or L = R₂NP(O)F₂; R = Me (4); Et (5)) are described. These new adducts have been characterised by multinuclear (¹⁹F, ³¹P and ¹¹⁹Sn) NMR, IR spectroscopy and elemental analysis. The NMR data particularly the ¹⁹F NMR spectra showed that the complexes exist in solution as mixtures of cis and trans isomers. The solution behaviour of the complexes studied by variable temperature NMR in the presence of excess ligand indicated that, unlike in the SnCl₄ analogues, the ligand exchange at room temperature is slow for 1–3 and fast only for 4 and 5. The metal–ligand exchange barriers in [SnF₄L₂] and [SnCl₄L₂] systems were estimated and compared. The results indicate that in addition to the difference in the Lewis acidity between SnF₄ and SnCl₄ the nature of the substituents (fluorine atoms) on the phosphorus atom of the ligand can contribute considerably to the lability of the complex obtained.     

Intramolecular mobility and phase transitions in ammonium oxofluoroniobates (NH4)2NbOF5 and (NH4)3NbOF6, a NMR and DFT study

Molecular structure, ionic mobility and phase transitions in six- and seven-coordinated ammonium oxofluoroniobates (NH₄)₂NbOF₅ and (NH₄)₃NbOF₆ were studied by ¹⁹F, ¹H NMR and DFT calculations. Equatorial fluorine atoms (F_eq) in [NbOF₅]²⁻ and [NbOF₆]³⁻ are characterized by high ¹⁹F NMR chemical shifts while axial fluorine atoms (F_ax) have those essentially lower. The high-temperature ionic mobility in (NH₄)₂NbOF₅ does not stimulate the ligand exchange F_eq ↔ F_ax, whereas it is observed in (NH₄)₃NbOF₆ as pseudorotation typical for seven-coordinated polyhedra. The transformation of pentagonal bipyramidal structure (BP) of [NbOF₆]³⁻ into capped trigonal prismatic (CTP) one takes place during the phase transition (PT) at 260 K. The PT of order-disorder type in (NH₄)₂NbOF₅ is accompanied by transition of anionic sublattice to a rigid state. The ¹⁹F and ¹H NMR data corroborate the independent motions of NH₄ groups and anionic polyhedra in (NH₄)₂NbOF₅ while they are coordinated in (NH₄)₃NbOF₆.     

A novel reaction producing the rhodium(I) complexes with π-coordinated tetraphenylborate anion, (π-PhBPh3). X-ray study of [Rh(PPh3)2(π-PhBPh3)]

Treating the complexes [Rh(TFA)(PPh₃)₂], [Rh(HFA)(PPh₃)₂], and [Rh(TFA)(Cod)] (TFA - trifluoroacetylacetonate, HFA - hexafluoroacetylacetonate, Cod - 1,5 cyclooctadiene) with an excess of NaBPh₄ in acetonitrile yields the rhodium(I) complexes with coordinated [BPh₄]⁻ anion, [Rh(PPh₃)₂(π-PhBPh₃)] · 2MeCN (I) and [Rh(Cod)(π-PhBPh₃)] (II). The reactions present a new example of β-diketonate ligand replacement. The ¹H, ³¹P, and ¹¹B NMR spectra of I and II are discussed. [Rh(PPh₃)₂(π-PhBPh₃)] has been characterized by single crystal X-ray analysis.     

Vacancy ordering and oxygen dynamics in oxide ion conducting La1−xSrxGa1−xMgxO3−x ceramics: Ga, Mg and O NMR

The oxygen vacancies distribution in the rigid lattice and the thermally activated motion of oxygen atoms are studied in La_1−xSr_xGa_1−xMg_xO_3−x (x=0.00; 0.05; 0.10; 0.15 and 0.20) compounds. For that ⁷¹Ga, ²⁵Mg and ¹⁷O NMR was performed from 100 K up to 670 K, and ion conductivity measurements were carried out up to 1273 K. The comparison of the electric field gradients at the Ga- and Mg-sites evidences that oxygen vacancies appear exclusively near gallium cations as a species trapped below room temperature in local clusters, GaO_5/2-□-GaO_5/2. These clusters decay at higher temperature into mobile constituents of the structural octahedra Ga(O_5/6□_1/6)_6/2. At the same time, the nearest octahedral oxygen environment of magnesium cations persists at different doping levels. The case of two adjacent vacant anion sites is found highly unlikely within the studied doping range. The thermally activated oxygen motion starts to develop above room temperature as is observed from both the motional narrowing of ¹⁷O NMR spectra and the ¹⁷O nuclear spin-lattice relaxation rate. The obtained results show that two types of motion exist, a slow motion and a fast one. The former is a long-range diffusion whereas the latter is a local back and forth oxygen jumps between two adjacent anion sites. These sites are strongly differentiated by the probability of the vacancy formation, like the vacant apical site and the occupied equatorial site in the orthorhombic compositions x <0.15.     

Antimony and silicon environments in antimony silicate glasses

Antimony silicate glasses, of general formula xSb₂O₃·(1−x)SiO₂ (0.1≤x≤0.78), have been prepared by melt-quenching and their structures studied using ²⁹Si MAS NMR spectroscopy, ¹²¹Sb Mössbauer spectroscopy and Raman spectroscopy. Oxidation during melting gives rise to Sb⁵⁺ in concentrations, which increase linearly with x to give a value of ∼10% when x=0.78. ¹²¹Sb Mössbauer spectra show Mössbauer shifts and quadrupole splittings consistent with Sb³⁺ in a [:SbO₃] trigonal pyramid, similar to that in crystalline Sb₂O₃. A broad band in the Raman spectrum at ∼410 cm⁻¹ is due to the vibrations of such a unit. The dependence of the silicon Qⁿ speciation on x can be interpreted by the formation of Sb-O-Sb links possibly to form rings of 4 [:SbO₃] units such as are found in valentinite.     

Comparative structural investigation of aluminium fluoride solvates

To get some insight by conclusions of analogy into the drying process of alcoholic aluminium fluoride sol–gels [AlF₃/(ROH)_x], the structures of α- and β-AlF₃3H₂O as well as of the nonahydrate AlF₃9H₂O are reinvestigated and discussed based on X-ray single crystal structural data. In addition, neutron diffraction experiments of the latter allowed the refinement of proton positions. In accordance with crystal structures, low-temperature solid state ²⁷Al-, ¹H- and ¹⁹F-MAS NMR spectra convincingly confirm the structural similarity between α-AlF₃3H₂O and AlF₃9H₂O, while the β-phase material is structurally different forming chain structures. Thermal analysis of AlF₃/(ROH)_x gave evidence for discrete AlF₃:ROH ratios of only 1:0.45 and 1:0.1, and solution NMR showed some similarities between aqueous and alcoholic systems.     

Crystalline aluminium hydroxy fluorides—Suitable reference compounds for F chemical shift trend analysis of related amorphous solids

On the basis of MAS NMR-data for crystalline AlF_x(OH)_3−x·H₂O samples in the pyrochlore structure, ¹⁹F chemical shifts correlate with the average chemical composition of the octahedral environment, given by AlF_xO_6−x in these compounds.The attribution of local structures in sol-gel derived amorphous AlF_x(OX)_3−x·XOH (X = H, R (alkyl)) compounds is of special interest as these or consecutively prepared solids exhibit remarkable features, for example, a high surface (HS) area accompanied by a high Lewis acidity.By transferring this scale of a ¹⁹F chemical shift trend analysis to such compounds a prediction of the chemical nature of the average Al coordination becomes possible.A new synthetic approach to crystalline aluminium hydroxy fluorides involving a sol gel fluorination as the first reaction step and an aluminium alkoxide as precursor compound is presented. Varying the amount of HF leads to different F-OH-ratios in the AlF_x(OH)_3−x compounds.     

1H, 13C, 15N NMR and 13C, 15N CPMAS studies of cobalt(III)-chloride-pyridine complexes, spontaneous py → Cl substitution in trans-[Co(py)4Cl2]Cl, and a new synthesis of mer-[Co(py)3Cl3]

trans-[Co(py)₄Cl₂]Cl·6H₂O, mer-[Co(py)₃Cl₃] and mer-[Co(py)₃(CO₃)Cl] were studied by UV-Vis, far-IR and ¹H, ¹³C, ¹⁵N NMR. The formation of Co-N bonds lead to variable in sign and magnitude changes of ¹H NMR chemical shifts, heavily dependent on proton position, coordination sphere geometry and character of auxiliary ligands. ¹³C nuclei were deshielded upon Co(III) coordination, while ¹⁵N NMR studies exhibited ca. 85–110 ppm shielding effects (ca. 15–25 ppm more expressed for nitrogens trans to N than trans to Cl or O). ¹³C and ¹⁵N CPMAS spectra revealed a slight inequivalency of formally identical Co-py bonds in trans-[Co(py)₄Cl₂]Cl·6H₂O and mer-[Co(py)₃Cl₃], suggesting for the latter complex an existence of distortion isomers. In chloroform, a spontaneous trans-[Co(py)₄Cl₂]Cl → mer-[Co(py)₃Cl₃] + py reaction was monitored by ¹H NMR and UV-Vis. This process of py → Cl substitution allowed the design of a more convenient and efficient method of mer-[Co(py)₃Cl₃] preparation.      

Synthesis, crystal structure, NMR data and thermogravimetrical properties of novel zirconium fluoride LiK10Zr6F35·2H2O

The synthesis and study (single crystal X-ray diffraction, thermogravimetry, IR- and NMR-spectroscopy) of a novel fluorozirconate LiK₁₀Zr₆F₃₅·2H₂O was performed. The structure of the compound is built from infinite chains _∞[Zr₆F₃₅]¹¹⁻, in which Zr-polyhedra are linked to each other through common edges and vertices. The chains are surrounded by K and Li cations and H₂O molecules. The compound dehydration occurs in the temperature range 453–543 K with maximal rate at 528 K. It was established that zirconium polyhedra chain fragments underwent reorientational motion starting to influence ¹⁹F NMR spectra at temperatures higher than 270 and 180 K in LiK₁₀Zr₆F₃₅·2H₂O and LiK₁₀Zr₆F₃₅, respectively. Above 450–420 K all fluorine sites in both samples participate in fluorine translational diffusion by at least two diffusion paths. Isotropic ¹⁹F NMR chemical shifts from different site types were detected by MAS NMR in the range 125–171 ppm.     

Hydrolysis of Volatile Ammonium Oxofluorotitanate According to 19F, 17O, and 49Ti NMR Data

Hydrolysis of NH₄TiO_xF_5-2x (x0.4) (I) was investigated by ¹⁹F, ¹⁷O, and ⁴⁹Ti NMR. The interaction of complex I with water is accompanied by the formation of [TiF₆]^2- and multinuclear titanium forms. The composition of the main forms resulting from hydrolysis of I has been established. The bonding of titanium octahedra into dimers and other oligomers occurs by formation of hydroxyl bridges, considerably lowering the pH of the solution. Close analogy has been found between hydrolysis of the title complex and that of titanium tetrafluoride.     

<Superscript>19</Superscript>F NMR spectroscopic characterization of the interaction of niflumic acid with human serum albumin

The interaction of a non-steroidal anti-inflammatory drug, niflumic acid (NFA), with human serum albumin (HSA) has been investigated by ¹⁹F nuclear magnetic resonance (NMR) spectroscopy. A ¹⁹F NMR spectrum of NFA in a buffered (pH 7.4) solution of NaCl (0.1 mol L⁻¹) contained a single sharp signal of its CF₃ group 14.33 ppm from the internal reference 2,2,2-trifluoroethanol. Addition of 0.6 mmol L⁻¹ HSA to the NFA buffer solution caused splitting of the CF₃ signal into two broadened signals, shifted to the lower fields of 14.56 and 15.06 ppm, with an approximate intensity ratio of 1:3. Denaturation of HSA by addition of 3.0 mol L⁻¹ guanidine hydrochloride (GU) restored a single sharp signal of CF₃ at 14.38 ppm, indicating complete liberation of NFA from HSA as a result of its denaturation. These results suggest that the binding is reversible and occurs in at least two HSA regions. Competitive ¹⁹F NMR experiments using warfarin, dansyl-l-asparagine, and benzocaine (site I ligands), and l-tryptophan and ibuprofen (site II ligands) revealed that NFA binds to site I at two different regions, Ia and Ib, in the ratio 1:3. By use of ¹⁹F NMR with NFA as an ¹⁹F NMR probe the nonfluorinated site I-binding drugs sulfobromophthalein and iophenoxic acid were also found to bind sites Ia and Ib, respectively. These results illustrate the usefulness and convenience of ¹⁹F NMR for investigation of the HSA binding of both fluorinated and nonfluorinated drugs.     

Li and Li MAS NMR Studies on Fast Ionic Conducting Spinel-Type Li2MgCl4, Li2-xCuxMgCl4, Li2-xNaxMgCl4, and Li2ZnCl4

⁶Li and ⁷Li MAS NMR spectra including 1D-EXSY (exchange spectroscopy) and inversion recovery experiments of fast ionic conducting Li₂MgCl₄, Li_2-xCu_xMgCl₄, Li_2-xNa_xMgCl₄, and Li₂ZnCl₄ have been recorded and discussed with respect to the dynamics and local structure of the lithium ions. The chemical shifts, intensities, and half-widths of the Li MAS NMR signals of the inverse spinel-type solid solutions Li_2-xM^I_xMgCl₄ (M^I=Cu, Na) with the copper ions solely at tetrahedral sites and sodium ions at octahedral sites and the normal spinel-type zinc compound, respectively, confirm the assignment of the low-field signal to Li^tet of inverse spinel-type Li₂MgCl₄ and the high-field signal to Lioct as proposed by Nagel et al. (2000). In contrast to spinel-type Li_2-2xMg_1+xCl₄ solid solutions with clustering of the vacancies and Mg²⁺ ions, the Cu⁺ and Na⁺ ions are randomly distributed on the tetrahedral and octahedral sites, respectively. The activation energies due to the various dynamic processes of the lithium ions in inverse spinel-type chlorides obtained by the NMR experiments are E_a=6.6-6.9 and ΔG^*>79 KJ mol⁻¹ (in addition to 23, 29, and 75 kJmol-1 obtained by other techniques), respectively. The largest activation energy of >79 KJ mol⁻¹ corresponds to hopping exchange processes of Li ions between the tetrahedral 8a sites and the octahedral 16d sites. The smallest value of 6.6-6.9 KJ mol⁻¹, which was derived from the temperature dependence of both the spin-lattice relaxation times T₁ and the correlation times τ_C of Li^tet, reveals a dynamic process for the Li^tet ions inside the tetrahedral voids of the structure, probably between fourfold 32e split sites around the tetrahedral 8a site.     

Phase transitions and molecular motions in [Cd(H2O)6](BF4)2 studied by DSC, H and F NMR and FT-MIR

Two solid phase transitions of [Cd(H₂O)₆](BF₄)₂ occurring on heating at T_C2=183.3 K and T_C1=325.3 K, with 2 K and 5 K hysteresis, respectively, were detected by differential scanning calorimetry (DSC). High value of entropy changes indicated large orientational disorder of the high temperature and intermediate phase. Nuclear magnetic resonance (¹H NMR and ¹⁹F NMR) relaxation measurements revealed that the phase transitions at T_C1 and T_C2 were associated with a drastic and small change, respectively, of the both spin-lattice relaxation times: T₁(¹H) and T₁(¹⁹F). These relaxation processes were connected with the “tumbling” motions of the [Cd(H₂O)₆]²⁺, reorientational motions of the H₂O ligands, and with the iso- and anisotropic reorientation of the BF₄⁻ anions. The cross-relaxation effect was observed in phase III. The line width and the second moment of the ¹H and ¹⁹F NMR line measurements revealed that the H₂O reorientate in all three phases of the title compound. On heating the onset of the reorientation of 3 H₂O in the [Cd(H₂O)₆]⁺², around the three-fold symmetry axis of these octahedron, causes the isotropic reorientation of the whole cation. The BF₄⁻ reorientate isotropically in the phases I and II, but in the phase III they perform slow reorientation only about three- or two-fold axes. A small distortion in the structure of BF₄⁻ as well as of [Cd(H₂O)₆]²⁺ is postulated. The temperature dependence of the bandwidth of the O-H stretching mode measured by Fourier transform middle infrared spectroscopy (FT-MIR) indicated that the activation energy for the reorientation of the H₂O did not change much at the T_C2 phase transition.     

Hydrolysis of ammonium oxofluorotungstates: A F, O and W NMR study

Fluorine-19 and natural abundance ¹⁷O and ¹⁸³W NMR spectroscopy were employed for the characterization of aqueous solutions of (NH₄)₂WO₂F₄ and (NH₄)₃WO₃F₃. Dissolution of the (NH₄)₂WO₂F₄ complex is accompanied by its partial acid hydrolysis to give the trans(mer)-dimer, [W₂O₅F₆]⁴⁻, and unreacted cis-[WO₂F₄]²⁻. The cis(fac)-[W₂O₅F₆]⁴⁻ anion is the major soluble product resulting from the alkaline hydrolysis of (NH₄)₂WO₂F₄ along with the isolation of the solid (NH₄)₂WO₃F₂. In addition, the edge-bridging dimer, [W₂O₆F₄]⁴⁻, and the cyclic trimer, [W₃O₉F₆]⁶⁻, are also suggested as hydrolysis products. Decomposition of (NH₄)₃WO₃F₃ occurs in aqueous solution to give NH₄WO₃F.     

Role of crystallite size on the photoluminescence properties of SrIn2O4:Eu phosphor synthesized by different methods

Photoluminescence (PL) of Eu³⁺ was studied in SrIn₂O₄ host lattice. A complete solid solubility of Eu³⁺ has been found in the series SrIn_2−xEu_xO₄ [x=0-2.0]. The phase formation at a relatively low temperature and in a very short duration was achieved by combustion synthesis (CS). Concentration quenching of luminescence has been observed in SrIn_2−xEu_xO₄ [x=0.1-2.0] and the critical concentration for maximum emission was found to be with x=0.3. In order to find the role of crystallite size on the PL properties of SrIn₂O₄:Eu³⁺, the results obtained with phosphors synthesized by solid state reaction (SSR) and CS methods were compared.     

Low temperature preparation and uses of potent oxidizers

Because electronegativity of an oxidation state is low in an anion, salts of the high oxidation-state species [AgF₄]⁻ and [NiF₆]²⁻ can be easily made, at 0 °C, in liquid anhydrous HF (aHF) made basic with alkali fluorides. The containers are transparent fluorocarbon, and the F₂ is photo-dissociated. The [NiF₆]²⁻ salts, and the metastable binary fluorides NiF₄ and NiF₃, derived from them, are efficient fluorinating agents for the conversion of hydrido compounds to their fully fluorinated relatives. With F₂ in aHF made acidic with fluoride-ion acceptors (e.g. MF₅, M = As, Sb, Bi) attained oxidation-states are often lower (e.g. Ag^II, Au^II) because of the higher electronegativity in cations. Cationic Ag^III and Ni^IV species (derived from the anions) are sufficiently long-lived, and potent, to generate the most powerfully oxidizing hexafluorides of the second and third transition series (i.e. [MF₆], M = Pt, Ru, Rh). This synthesis is especially valuable for RhF₆, and has provided for the reinvestigation of the interaction of it with O₂. It is proposed that the unexpectedly large unit cell of O₂RhF₆ is a result of the presence of neutral O₂ and neutral RhF₆ as well as O₂⁺ and RhF₆⁻ in the lattice.