Gas-phase negative ions of platinum metal fluorides. II. Electron affinity of platinum metal hexafluorides

Reactions of platinum metal hexafluoride negative ions were studied by Knudsen cell mass spectrometry. The electron affinities were measured for OsF₆(5.93±0.28 eV), IrF₆ (6.50±0.38 eV), PtF₆(7.00±0.35 eV), and RuF₆ (6.47±0.31 eV).The relevant data on electron affinities of platinum metal hexafluorides are discussed.     

Nitrosyl,nitryl and dioxygenyl hexafluoroplatinate(IV) and (V) and related compounds: Synthesis,reactions and raman spectra

The reactions of PtF₅, O₂PtF₆, PtF₆, IrF₆, NOPtF₆, NO₂PtF₆, NOIrF₆ and NO₂IrF₆ with NOF and NO₂F have been examined under a variety of conditions. The relative ease of synthesis of NOPtF₆, (NO)₂PtF₆, NOIrF₆ and NO₂IrF₆ and the conversion of NOIrF₆ to NOPtF₆ with PtF₆ confirms the order of strong oxidizing properties of Pt^VIF₆, Ir^VIF₆, Pt^VF^-₆ and Ir^VF^-₆. The NO⁺₂ ion is intrinsically unstable with respect to the elimination of oxygen in Pt (IV) and Ir (IV) fluorometallate salts and accordingly there is serious doubt about earlier claims for the synthesis of the (NO⁺)(NO⁺₂)PtF₆ salt. No evidence for the (NO₂)₂PtF₆ could be found.Raman spectral data for NOBF₄, NO₂BF₄, NO₂AsF₆, NOPtF₆, NO₂PtF₆, (NO)₂PtF₆, NOIrF₆, NO₂IrF₆ and (NO)₂IrF₆ are presented and analyzed. The NO⁺₂ ion appears to be linear in all of the compounds and the absence of the Raman forbidden ν₂ fundamental indicates little if any anion-cation interaction at least of the type that leads to a permanent distortion of the cation. In the spectra of all of the nitryl salts, including NO₂BF₄, a low frequency band at about 140 cm^-1 is clearly observed, the intensity and shape of which is a function of the anion. The band probably reflects an unknown lattice dynamic process. No such bands are evident in the spectra of NO⁺ and (NO⁺)₂ salts.     

The Oxidizing Properties of the Third Transition Series Hexafluorides and Related Compounds

Some of the transition metal hexafluorides demonstrate an astonishing oxidizing power. In particular may be mentioned PtF₆, which is capable of oxidizing molecular oxygen or xenon, a process requiring an electron affinity, E(PtF₆), > ?156 kcal·mole^?1. From a comparative study of all of the hexafluorides of the third transition series the electron affinity is seen to increase regularly in the sequence WF₆ < ReF₆ < OsF₆ < IrF₆ < PtF₆. The increase in E with unit increase in atomic number of M appears to be ≈ ?20 kcal·mole^?1. On the other hand the ability of the hexafluorides to accept F^? decreases along this series. This effect enables IrF₆ to be more effective than PtF₆ in the generation of nitrogen oxide trifluoride, ONF₃, by the oxidative fluorination of nitrosyl fluoride, ONF. Both PtF₆ and IrF₆ interact spontaneously with ONF or O₂NF to generate fluorine, at or below room temperature. The decrease in F^? -acceptor ability along the series, which stands in sharp contrast to the increase in electron affinity, suggests that ligand crowding increases sharply across the series from WF₆ to PtF₆. This accords with the observed decrease in molecular volume along the series, both in the hexafluorides and in the MF₆^? salts. It is clear from this comparison that the species IrF₆ and PtF₆ are close to a minimum volume for this series. The oxide pentafluorides ReOF₅ and OsOF₅ are similar in oxidizing ability to their respective hexafluorides but are poorer F^? acceptors. Evidently the ligand crowding in MOF₅ molecules is greater than in MF₆.     

Kernresonanzuntersuchungen an Hexafluoriden

N.M.R. Measurements on Hexafluorides ¹⁹F n.m.r. spectra of natural and ¹²⁹Xe enriched XeF₆, ²³⁸UF₆, ²³⁵UF₆, PtF₆, IrF₆, OsF₆ and AuF₆^? were measured and interpretated. The tetramerisation of XeF₆ at low temperatures can be confirmed.     

ReF7 and ReOF5 as fluoride ion donors

Salts containing the ReF₆⁺ ion have been prepared by one-electron oxidation of ReF₆ using KrF⁺ salts. The compounds ReF₆⁺MF₆^? (M = Au, Sb) are of moderate stability, tending to decompose to ReF₇ and the corresponding pentafluoride. This gives rise to isolated ReF₇ and MF₅ molecules within the ionic lattice, whose presence is demonstrated by Raman spectroscopy. Interaction of ReF₆ and PtF₆ produced not the salt ReF₆⁺PtF₆^? (1), but rather the deep red (PtF₅)₄ when PtF₆ was present in excess, and PtF₄ when ReF₆ was in excess. ReF₆ and IrF₆ appear to be in equilibrium with ReF₇ and (IrF₅)₄, possibly via an ionic intermediate ReF₆⁺(IrF₆·xIrF₅)^?.The salts ReOF₄⁺MF_6? (M = As, Au, Sb) have been characterized. In contrast to the behaviour of IOF₅ and IF₇, ReOF₅ is a better fluoride ion donor than ReF₇.     

Exploring the Limits of Transition-Metal Fluorination at High Pressures

Fluorination is a proven method for challenging the limits of chemistry, both structurally and electronically. Here we explore computationally how pressures below 300 GPa affect the fluorination of several transition metals. A plethora of new structural phases are predicted along with the possibility for synthesizing four unobserved compounds: TcF₇, CdF₃, OsF₈, and IrF₈. The Ir and Os octaflourides are both predicted to be stable as quasi-molecular phases with an unusual cubic ligand coordination, and both compounds formally correspond to a high oxidation state of +8. Electronic-structure analysis reveals that otherwise unoccupied 6p levels are brought down in energy by the combined effects of pressure and a strong ligand field. The valence expansion of Os and Ir enables ligand-to-metal F 2p→M 6p charge transfer that strengthens M−F bonds and decreases the overall bond polarity. The lower stability of IrF₈, and the instability of PtF₈ and several other compounds below 300 GPa, is explained by the occupation of M−F antibonding orbitals in octafluorides with a metal-valence-electron count exceeding 8.     

Exploring the Limits of Transition‐Metal Fluorination at High Pressures

Fluorination is a proven method for challenging the limits of chemistry, both structurally and electronically. Here we explore computationally how pressures below 300 GPa affect the fluorination of several transition metals. A plethora of new structural phases are predicted along with the possibility for synthesizing four unobserved compounds: TcF₇, CdF₃, OsF₈, and IrF₈. The Ir and Os octaflourides are both predicted to be stable as quasi‐molecular phases with an unusual cubic ligand coordination, and both compounds formally correspond to a high oxidation state of +8. Electronic‐structure analysis reveals that otherwise unoccupied 6p levels are brought down in energy by the combined effects of pressure and a strong ligand field. The valence expansion of Os and Ir enables ligand‐to‐metal F 2p→M 6p charge transfer that strengthens M?F bonds and decreases the overall bond polarity. The lower stability of IrF₈, and the instability of PtF₈ and several other compounds below 300 GPa, is explained by the occupation of M?F antibonding orbitals in octafluorides with a metal‐valence‐electron count exceeding 8.     

Why Aren't There Any Trioxygenyl or Ozonium Salts? Or,Why Does Our Reaction of O3 and PtF6 Give O2PtF6?

The reaction of ozone and gaseous platinum hexafluoride led to O₂PtF₆(s) and not the desired O₃PtF₆(s). Suggestions as to why the synthesis of O₃PtF₆(s) failed are made in terms of the known chemistry of the gaseous O ₃ ⁺ cation with O ₊ ⁵ proposed as an intermediate.     

Three hexafluoridoiridates(IV), Ca[IrF6]·2H2O,Sr[IrF6]·2H2O and Ba[IrF6]

The structures of the hexafluoridoiridates(IV) of calcium, Ca[IrF₆]·2H₂O [calcium hexafluoridoiridate(IV) dihydrate], strontium, Sr[IrF₆]·2H₂O [strontium hexafluoridoiridate(IV) dihydrate], and barium, Ba[IrF₆] [barium hexafluoridoiridate(IV)], have been determined by single‐crystal X‐ray analysis. The first two compounds are isomorphous. Their metal cations are eight‐coordinated in a distorted square‐antiprismatic coordination environment, and their anions are represented by an almost ideal octahedron. These two structures can be described as frameworks in which all atoms occupy general positions. Sr[RhF₆] and Ba[RhF₆] have a different space group (, from powder diffraction data) but similar cell dimensions. The structures are very close to that of Ba[IrF₆]. The cation is in a cuboctahedral coordination. The metal atoms are located on special positions of symmetry, while the F atoms are in general positions.     

Hydrolysis reactions of transition metal fluorides in liquid hydrogen fluoride: Oxonium salts with Nb,Ta and W

The hydrolysis reactions of the hexafluorides of molybdenum and tungsten, the pentafluorides of niobium and tantalum and the tetrafluorides of zirconium and hafnium have been studied in liquid hydrogen fluoride. The following new compounds have been isolated and characterized: H₃O⁺WOF^-₅, H₃O⁺NbF^-₆ and H₃O⁺TaF^-₆. Hydrolysis of MoF₆ leads to MoOF₄, but in HF solution there is evidence for the existence of MoOF^-₅ ion.     

Einkristalluntersuchungen an LiMF6 (M = Rh,Ir), Li2RhF6 und K2IrF6

Single Crystal Investigations on LiMF₆ (M = Rh, Ir), Li₂RhF₆, and K₂IrF₆ LiRhF₆, LiIrF₆, Li₂RhF₆, and K₂IrF₆ were obtained again, but for the first time investigated by single crystal X‐ray methods. Rubyred LiRhF₆ and yellow LiIrF₆ crystallize isostructural in the trigonal space group R3 – C²_3i (Nr. 148) with the lattice parameters LiRhF₆: a = 502.018(7) pm, c = 1355.88(3) pm, Z = 3 and d(Rh–F) = 185.5(1) pm; LiIrF₆: a = 506.148(4) pm, c = 1362.60(2) pm, Z = 3, d(Ir–F) = 187.5(3) pm (LiSbF₆‐Typ). Yellow Li₂RhF₆ crystallizes tetragonal in the space group P4₂/mnm – D¹⁴_4h (Nr. 136) with a = 463.880(8) pm, c = 905.57(2) pm, Z = 2 and d(Rh–F) = 190.3(4)–191.4(3) pm (Trirutil‐Typ). Yellow K₂IrF₆ crystallizes trigonal in the space group P3m1 – D³_3d (Nr. 164) with a = 578.88(7) pm, c = 465.06(5) pm, Z = 1 and d(Ir–F) = 194.0(6) pm, isotypic with K₂GeF₆.     

Noble gas compounds and chemistry: a brief review of interrelations and interactions with fluorine-containing species

This review is composed of six vignettes. They deal with respectively: the reaction of Xe and PtF₆; the reaction of O₂ and O₃ with PtF₆; salts of O⁺, the covalent OF, and noble gas-containing cations; synthesis, reactions and structure of [XeO₂]⁺ en route to [XeF]⁺ salts; [Xe₂]⁺, green and related species; neutral xenon oxides, nonmetal oxyanions, and a nonmetal fluoride “mid-valence” crisis. Interrelations and interactions are emphasized.     

Oxygen analysis of O2MF6 and O2M2F11 salts

The dioxygenyl salts O₂MF₆ or O₂M₂F₁₁ where M = As, Sb, Bi, Nb, Ta, Ru, Au, and Pt, were hydrolysed aqueous base (40% NaOH) to evaluate their purity and to gain further information about their thermal instability. Compounds containing As, Sb, Bi, Nb and Ta yielded 1.25 moles O₂ per mole of starting material whereas for compounds containing Ru, Au and Pt, 1.5 moles of O₂ per mole of salt was produced. The difference is a consequence of the greater oxidizing power of the RuF^-₆, AuF^-₆ and PtF^-₆ anions. All of the dioxygenyl salts are intrinsically unstable at room temperature in vacuum.     

The Mixed Valence Structure of “R–NiF3”

XAS at the nickel K-edge and UV-visible studies of rhombohedral nickel trifluoride indicate that the compound has a mixed valence composition Ni[NiF₆] and is isostructural with Pd[PdF₆]. XAS data are reported for NiF₂, [NiF₆]^2–, [NiF₆]^3–, Pd[PdF₆], CoF₃ and RhF₃ in support of the Ni[NiF₆] study. New data from refinements of X-ray powder diffraction of CoF₃ and IrF₃ are reported in the context of the distortion from hexagonal close packing of rhombohedral trifluorides.     

A specific method for the preparation of many transition metal and actinide oxide tetrafluorides

A general method for the preparation of many transition metal and actinide oxide tetrafluorides by oxygen-fluorine exchange of their respective hexafluorides using boric oxides is described. This simple procedure affords the preparation of MoOF₄, WOF₄, ReOF₄, OsOF₄ and UOF₄ in high yield while reaction of boric oxide with IrF₆ and RuF₆ leads to the preparation of lower fluorides of these elements. The preparation of oxide tetrafluorides by reaction of their oxide tetrachlorides with anhydrous HF has also been investigated, as well as a study of some halogen-exchange reactions of the oxide tetrafluorides.     

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.     

Kristallstrukturen,Schwingungsspektren und Normalkoordinatenanalyse von fac‐(Et4N)[OsF3Cl3] und fac‐(Et4N)[IrF3Cl3]

Crystal Structures, Vibrational Spectra and Normal Coordinate Analysis of fac ‐(Et₄N)[OsF₃Cl₃] and fac ‐(Et₄N)[IrF₃Cl₃] By careful oxidation of the pure fluorochloroosmates(IV) or ‐iridates(IV) with BrF₃ or KBrF₄ in dichloromethane the mixed pentavalent complex anions fac‐[OsF₃Cl₃]^– and fac‐[IrF₃Cl₃]^– are formed. X‐ray structure determinations on single crystals have been performed of cis‐(Et₄N)[OsF₃Cl₃] ( 1 ) (orthorhombic, space group Pbca, a = 11.225(5), b = 12.020(5), c = 21.873(5) Å, Z = 8) and fac‐(Et₄N)[IrF₃Cl₃] ( 2 ) (orthorhombic, space group Pbca, a = 11.269(10) b = 12.049(1), c = 21.801(3) Å, Z = 8). Based on the molecular parameters of the X‐ray determinations the IR and Raman spectra for the anion of 1 and 2 have been assigned by normal coordinate analysis. The Osmium compound exhibits slightly higher valence force constants as compared with the Iridium complex: f_d(OsF) = 3.25, f_d(IrF) = 3.25, f_d(OsCl) = 2.35 and f_d(IrCl) = 2.25 mdyn/Å.     

Matrix Isolation Spectroscopic and Relativistic Quantum Chemical Study of Molecular Platinum Fluorides PtFn (n=1–6) Reveals Magnetic Bistability of PtF4

Molecular platinum fluorides PtF_n, n=1–6, are prepared by two different routes, photo-initiated fluorine elimination from PtF₆ embedded in solid noble-gas matrices, and the reaction of elemental fluorine with laser-ablated platinum atoms. IR spectra of the reaction products isolated in rare-gas matrices under cryogenic conditions provide, for the first time, experimental vibrational frequencies of molecular PtF₃, PtF₄ and PtF₅. Photolysis of PtF₆ enabled a highly efficient and almost quantitative formation of molecular PtF₄, whereas both PtF₅ and PtF₃ were formed simultaneously by subsequent UV irradiation of PtF₄. The vibrational spectra of these molecular platinum fluorides were assigned with the help of one- and two-component quasirelativistic DFT computation to account for scalar relativistic and spin–orbit coupling effects. Competing Jahn-Teller and spin–orbit coupling effects result in a magnetic bistability of PtF₄, for which a spin-triplet (³B_2g, D_2h) coexists with an electronic singlet state (¹A_1g, D_4h) in solid neon matrices.     

High-Spin Iron(VI), Low-Spin Ruthenium(VI), and Magnetically Bistable Osmium(VI) in Molecular Group 8 Nitrido Trifluorides NMF3

Pseudo-tetrahedral nitrido trifluorides N≡MF₃ (M=Fe, Ru, Os) and square pyramidal nitrido tetrafluorides N≡MF₄ (M=Ru, Os) were formed by free-metal-atom reactions with NF₃ and subsequently isolated in solid neon at 5 K. Their IR spectra were recorded and analyzed aided by quantum-chemical calculations. For a d² electron configuration of the N≡MF₃ compounds in C_3v symmetry, Hund's rule predict a high-spin ³A₂ ground state with two parallel spin electrons and two degenerate metal d(δ)-orbitals. The corresponding high-spin ³A₂ ground state was, however, only found for N≡FeF₃, the first experimentally verified neutral nitrido Fe^VI species. The valence-isoelectronic N≡RuF₃ and N≡OsF₃ adopt different angular distorted singlet structures. For N≡RuF₃, the triplet ³A₂ state is only 5 kJ mol⁻¹ higher in energy than the singlet ¹A′ ground state, and the magnetically bistable molecular N≡OsF₃ with two distorted near degenerate ¹A′ and ³A“ electronic states were experimentally detected at 5 K in solid neon.     

Dissociative Photoionization of 1,4-Dioxane with Tunable VUV Synchrotron Radiation

The photoionization and photodissociation of 1,4-dioxane have been investigated with a reflectron time-of-flight photoionization mass spectrometry and a tunable vacuum ultraviolet synchrotron radiation in the energy region of 8.0-15.5 eV. Parent ion and fragment ions at m/z 88, 87, 58, 57, 45, 44, 43, 41, 31, 30, 29, 28 and 15 are detected under supersonic conditions. The ionization energy of DX as well as the appearance energies of its fragment ions C₄H₇O₂⁺, C₃H₆O⁺, C₃H₅O⁺, C₂H₅O⁺, C₂H₄O⁺, C₂H₃O⁺, C₃H₅⁺, CH₃O⁺, C₂H₆⁺, C₂H₅⁺/CHO⁺, C₂H₄⁺ and CH₃⁺ was determined from their photoionization efficiency curves. The optimized structures for the neutrals, cations, transition states and intermediates related to photodissociation of DX are characterized at the B3LYP/6-31+G(d,p) level and their energies are obtained by G3B3 method. Possible dissociative channels of the DX are proposed based on comparison of experimental AE values and theoretical predicted ones. Intramolecular hydrogen migrations are found to be the dominant processes in most of the fragmentation pathways of 1,4-dioxane.