Further Insights into the Chemical Synthesis of F2 and on Drying moist HF.

It is well established that solid K2MnF6 reacts with excess SbF5 forming elemental F2. However, if the reaction is carried out in anhydrous HF (aHF) as a solvent, this is surprisingly not the case. Instead, the green Mn(IV) compound K3[(MnIVF)(SbF6)5]F is obtained. The reductive elimination of F2 was not observed under the applied conditions. The compound was characterized by its crystal structure, by Raman spectroscopy, and by quantum-chemical solid-state calculations. It crystallizes in the monoclinic space group P21/c, mP164, with the lattice parameters a = 12.2393(13), b = 12.167(2), c = 20.115(5) Å, ß = 110.805(8)°, V = 2800.1(9) Å3, Z = 4 at T = 200 K. As the use of strictly anhydrous HF is crucial in this and other similar reactions, methods for drying moist HF are discussed.

The Crucial Role of Sb2 F10 in the Chemical Synthesis of F2.

The purely chemical synthesis of fluorine is a spectacular reaction which for more than a century had been believed to be impossible. In 1986, it was finally experimentally achieved, but since then this important reaction has not been further studied and its detailed mechanism had been a mystery. The known thermal stability of MnF4 casts serious doubts on the originally proposed hypothesis that MnF4 is thermodynamically unstable and decomposes spontaneously to a lower manganese fluoride and F2 . This apparent discrepancy has now been resolved experimentally and by electronic structure calculations. It is shown that the reductive elimination of F2 requires a large excess of SbF5 and occurs in the last reaction step when in the intermediate [SbF6 ][MnF2 ][Sb2 F11 ] the addition of one more SbF5 molecule to the [SbF6 ]- anion generates a second tridentate [Sb2 F11 ]- anion. The two tridentate [Sb2 F11 ]- anions then provide six fluorine bridges to the Mn atom thereby facilitating the reductive elimination of the two fluorine ligands as F2 .

Fluoro-nitrogen Cations.

The crystal structures of [NH3 F]+ [CF3 SO3 ]- , [NH2 F2 ]+ [SbF6 ]- , and [N2 F3 ]+ [Sb3 F16 ]- have been determined, representing the first structural characterizations of these simple fluoro-nitrogen cations. The influences of the hybridization of the central nitrogen atom and of the number of fluorine substituents on the N-F bond lengths are evaluated for the series N2 F+ , N2 F3 + , NF2 O+ , NH3 F+ , NH2 F2 + , and NF4 + . It is shown that the N-F bond length decreases from 1.40 Što 1.26 Šwith increasing fluorine substitution and increasing s-character of the nitrogen atom, and that unusual N-F bond lengths reported in the previous literature are caused by disorder problems.

Energetic Properties, Spectroscopy, and Reactivity of NF3O.

The heats of formation of NF3O and similar C, S, and Si systems are predicted using the accurate composite computational chemistry Feller-Peterson-Dixon (FPD) method. The harmonic vibrational frequencies at the CCSD(T)/aug-cc-pVTZ level are reported and compared to the experimental values for NF3O, its isoelectronic species CF3O- and NF4+, and NF3. The infrared intensities were calculated at the MP2/aug-cc-pVTZ level and show that the infrared absorption is predicted to be like those of CF2Cl2 and SF6 within a factor of ∼2. The calculated heats of formation are in good agreement with the available experimental values. These heats of formation are used to calculate a range of bond dissociation energies (BDEs). It is predicted that NF3O is unlikely to decompose either thermally or photolytically in the troposphere. The potential energy curves for the decomposition of NF3O to NF2O + F are all repulsive, as are the channels to form NF3 and either O3P or O1D. The predicted persistence of NF3O in the troposphere is attributed to the high barrier of its reaction with the OH radical and that light with the wavelength needed for its photodissociation will not reach the troposphere. Reliable experimental measurements of the global warming potential of NF3O are needed to confirm our predictions that NF3O is like NF3 in this respect.

Protonation of CH3 N3 and CF3 N3 in Superacids: Isolation and Structural Characterization of Long-Lived Methyl- and Trifluoromethylamino Diazonium Ions.

The methylamino diazonium cations [CH3 N(H)N2 ]+ and [CF3 N(H)N2 ]+ were prepared as their low-temperature stable [AsF6 ]- salts by protonation of azidomethane and azidotrifluoromethane in superacidic systems. They were characterized by NMR and Raman spectroscopy. Unequivocal proof of the protonation site was obtained by the crystal structures of both salts, confirming the formation of alkylamino diazonium ions. The Lewis adducts CH3 N3 ⋅AsF5 and CF3 N3 ⋅AsF5 were also prepared and characterized by low-temperature NMR and Raman spectroscopy, and also by X-ray structure determination for CH3 N3 ⋅AsF5 . Electronic structure calculations were performed to provide additional insights. Attempted electrophilic amination of aromatics such as benzene and toluene with methyl- and trifluoromethylamino diazonium ions were unsuccessful.

Electronic Structure Predictions of the Energetic Properties of Tellurium Fluorides.

The heats of formation, bond dissociation energies (BDEs), fluoride affinities (FA), fluorocation affinities (FCA), electron affinities (EA), and ionization energies (IP) of TeF n ( n = 1-6) have been predicted using the Feller-Peterson-Dixon (FPD) approach. To benchmark the approach, the bond dissociation energies of Te2 and TeO, the heats of formation of Te2, TeH2, TeO, and TeO2, and the electron affinity for TeO and TeO2 were calculated as there are experimental thermodynamic data available for these tellurium compounds, which allow confirmation of the heat of formation of Te gas as Δ Hf,0K(Te) = 50.7 ± 0.6 kcal/mol. Spin-orbit corrections are required for good results and cannot be ignored. A comparison among fluoride affinities, fluorocation affinities, electron affinities, and ionization energies of TeF n and SeF n is reported.

Formamidinium Nitroformate: An Insensitive RDX Alternative.

Five nitroformate (trinitromethanide) salts featuring nitrogen-containing cations were prepared. The salts were characterized by multinuclear NMR, IR, and Raman spectroscopy, single-crystal X-ray analysis, differential thermal analysis, and friction and impact sensitivity testing. These experimental data are supplemented with thermochemical calculations using the Gaussian-4 composite method, and the performance of these energetic materials was calculated based on the Chapman-Jouguet thermodynamic detonation theory. Out of the five compounds studied by us, the formamidinium salt, [CH(NH2)2]+[C(NO2)3]-, is most interesting. Its performance matches that of RDX (research department explosive, cyclotrimethylenetrinitramine), while it is much less sensitive to impact and friction and, therefore, might be an excellent, less sensitive replacement for RDX.

Synthesis and Characterization of cyclo-Pentazolate Salts of NH4+, NH3OH+, N2H5+, C(NH2)3+, and N(CH3)4.

A breakthrough in polynitrogen chemistry was recently achieved by our bulk synthesis of (N5)6(H3O)3(NH4)4Cl in which the cyclo-pentazolate anions were stabilized extensively by hydrogen bridges with the NH4+ and OH3+ cations. Significant efforts have been carried out to replace these nonenergetic cations and the Cl- anion by more energetic cations. In this paper, the metathetical syntheses of cyclo-pentazolate salts containing the simple nitrogen-rich cations NH4+, NH3OH+, N2H5+, C(NH2)3+, and N(CH3)4+ are reported. These salts were characterized by their crystal structures; vibrational, mass, and multinuclear NMR spectra; thermal stability measurements; sensitivity data; and performance calculations. It is shown that the cyclo-pentazolates are more energetic than the corresponding azides but are thermally less stable decomposing in the range of 80 °C to 105 °C. As explosives, the hydrazinium and hydroxyl ammonium salts are predicted to match the detonation pressure of RDX but exhibit significantly higher detonation velocities than RDX and HMX with comparable impact and friction sensitivities. Although the ammonium salt has a lower detonation pressure than RDX, its detonation velocity also exceeds those of RDX and HMX. As a rocket propellant, the hydrazinium and hydroxyl ammonium salts are predicted to exceed the performances of RDX and HMX. The crystal structures show that the cyclo-pentazolate anions are generally stabilized by hydrogen bonds to the cations, except for the N(CH3)4+ salt which also exhibits strong cation-π interactions. This difference in the anion stabilization is also detectable in the vibrational spectra which show for the N(CH3)4+ salt a decrease in the cyclo-N5- stretching vibrations of about 20 cm-1.

α-Fluoroalcohols: Synthesis and Characterization of Perfluorinated Methanol, Ethanol and n-Propanol, and their Oxonium Salts.

The thermally unstable, primary perfluoroalcohols, CF3 OH, C2 F5 OH, and nC3 F7 OH, were conveniently prepared from the corresponding carbonyl compounds in anhydrous HF solution. Experimental values for the reaction enthalpies and entropies were derived from the temperature dependence of the Rf COF+HF⇄Rf CF2 OH (Rf =F, CF3 , CF3 CF2 ) equilibria by NMR spectroscopy. Electronic structure calculations of the gas-phase and solution reaction energies, gas-phase acidities and heats of formation were carried out at the G3MP2 level, showing that these compounds are strong acids. Protonation of these alcohols in HF/SbF5 produced the perfluoroalkyl oxonium salts Rf CF2 OH2 + SbF6 - .

Perfluoroalcohols: The Preparation and Crystal Structures of Heptafluorocyclobutanol and Hexafluorocyclobutane-1,1-diol.

The first X-ray crystal structure of an α-fluoroalcohol is reported. Heptafluorocyclobutanol was obtained in quantitative yield from hexafluorocyclobutanone by HF addition in anhydrous hydrogen fluoride. The compound was characterized by its X-ray single crystal structure. Heptafluorocyclobutanol readily undergoes hydrolysis to hexafluorocyclobutane-1,1-diol, which was also structurally characterized by X-ray diffraction.