The xenon-fluoride bond dissociation energy in XeF3- has been measured by using energy-resolved collision-induced dissociation studies of the ion. The measured value, 0.84 +/- 0.06 eV, is higher than that predicted by electrostatic and three-center, four-electron bonding models. The bonding in XeF3- is qualitatively described by using molecular orbital approaches, using either a diradical approach or orbital interaction models. Two low-energy singlet structures are identified for XeF3-, consisting of Y- and T-shaped geometries, and there is a higher energy D3h triplet state. Electronic structure calculations predict the Y geometry to be the lowest energy structure, which can rearrange by pseudorotation through the T geometry. Orbital correlation diagrams indicate that that ion dissociates by first rearranging to the T structure before losing fluoride.

The sulfur-containing diazenes ArSNC(Ar‘)NNC(Ar‘)NSAr (1d, Ar = Ar‘ = 4-CH3C6H4; 3b, Ar = Ph, Ar‘ = 2-BrC6H4; 3c, Ar = Ph, Ar‘ = 2-CF3C6H4) are obtained by the reaction of Ar‘CN2(SiMe3)3 with 3 molar equivs of ArSCl in CH2Cl2. X-ray structural determinations have shown that 1d exists as a Z,E,Z isomer with a weak intramolecular S···N interaction [2.607(10) Å], whereas 3b adopts an E,E,E configuration. Crystals of 1d are monoclinic, space group P21/n, with a = 6.140(2) Å, b = 10.492(6) Å, c = 20.728(9) Å, β = 96.56(4)°, V = 1325(1) Å3, Z = 2, R = 0.056, and R w = 0.052. Crystals of 3b are orthorhombic, space group Ccca, with a = 13.884(5) Å, b = 24.763(7) Å, c = 14.500(3) Å, V = 4985(2) Å3, Z = 8, R = 0.043, and R w = 0.044. Density functional theory calculations for the model diazenes HENC(H)NNC(H)NEH (E = S, Se, Te) show that (a) Z,E,Z isomers with an intramolecular E···N interaction are more stable than the E,E,E isomers, (b) the intramolecular interaction involves donation from the σ(N) lone pairs into both σ*(S−H) and σ*(S−N) and back-donation from a chalcogen π lone pair into the π*(NN) orbital, and (c) the intense visible absorption bands (λmax 500−550 nm, ε = 1 × 104 M-1 cm-1) can be attributed to the π-HOMO (3au) → π*-LUMO (3bg) transition. Variable-temperature 1H NMR spectra of PhSNC(H)NNC(H)NSPh in toluene-d 8 and in CD2Cl2 provide evidence for the co-existence and interconversion of several geometrical isomers.

Supplemental Figure S1, mass spectra of the reaction of OH − (H 2 O) n with FSi(CH 3 ) 3 for n = 1 -3 (a -c, respectively). Scheme S1, computations for conformations of 1, 2 and 3A. Tables S1 -S3.Listings of B3LYP/6-31+G* geometries, unscaled frequencies, Mulliken charges, absolute energies and 298 K enthalpies for structures A, B, C, AB, and AC for 1, 2, and 3. Tables S4 -S22.Listings of B3LYP/aug-cc-pVDZ, B3LYP/aug-cc-pVTZ and MP2/aug-cc-pVDZ geometries, unscaled frequencies, absolute energies and 298 K enthalpies for structures 1A, 1AB and 1B. Single point energies for B3LYP/6-31+G*, B3LYP/aug-cc-pVDZ. B3LYP/aug-cc-pVTZ and MP2/aug-cc-pVDZ structures of 1A, 1AB and 1B at different levels of theory. Tables S23 -S36.Listings of B3LYP/6-31+G* geometries, unscaled frequencies, absolute energies and 298 K enthalpies for all other relevant species, including neutrals and anions. Tables S37 -S75.

No abstract

This study focuses upon the Lewis acid reactivity of XeF(+) with various bases in the gas phase and the determination of the bond dissociation energy of XeF(+). The bond dissociation energy of XeF(+) has been measured by using energy-resolved collision-induced dissociation with neon, argon, and xenon target gases. Experiments with neon target yield a 298 K bond dissociation enthalpy of 2.81 +/- 0.09 eV, and those with argon target give a similar value at 2.83 +/- 0.12 eV. When using a xenon target, a significantly lower value of 1.95 +/- 0.16 eV was observed, which corresponds closely with previous measurements and theoretical predictions. It is proposed that the lighter target gases give inefficient excitation of the XeF(+) vibration leading to dissociation at energies higher than the BDE. Novel xenon-base adducts have been prepared in a flowing afterglow mass spectrometer by termolecular addition to XeF(+) and by reaction of base with XeF(+)(H(2)O). New species have been characterized qualitatively by CID, and it is found that the products formed reflect the relative ionization energies of the fragments. Among the new xenon-containing species that have been prepared are the first examples of xenon carbonyls.

In this study, preparation and decomposition of five novel pentavalent fluorosiliconates, RSi(CH 3 ) 3 F Ϫ (R ϭ CH 3 CH 2 O, CF 3 CH 2 O, (CH 3 ) 2 CHO, (CH 3 ) 3 SiO, and (CH 3 ) 3 SiNH) is used to investigate the process of fluoride-induced desilylation. The siliconates were characterized by collision-induced dissociation and energy-resolved mass spectrometry. Decomposition of RSi(CH 3 ) 3 F Ϫ leads to loss of the nucleophile R Ϫ and FSi(CH 3 ) 3 , except in the case of (CH 3 ) 3 SiNHSi(CH 3 ) 3 F Ϫ , where HF loss is also observed. Ion affinities for FSi(CH 3 ) 3 have been measured for all five nucleophiles, and compare well with computational predictions. The observed trend of the bond dissociation energies resembles the trend of ⌬H acid values for the corresponding conjugate acids, RH. Additionally, this data has been incorporated with existing thermochemistry to derive fluoride affinities for four of the silanes (R ϭ CH 3 CH 2 O, (CH 3 ) 2 CHO, (CH 3 ) 3 SiO, and (CH 3 ) 3 SiNH). We use the fluoride affinity of the silanes and the FSi(CH 3 ) 3 affinity of the departing nucleophilic anion to assess the feasibility of fluorideinduced desilylation of the silanes examined in this work. (J Am Soc Mass Spectrom 2005, 16, 697-707)

Hydrogen cyanide (HCN) for use in ion preparation can be generated in the gas phase by the neutral-neutral reaction of trimethylsilyl cyanide (Me 3 SiCN) and water in a flowing afterglow mass spectrometer. We demonstrate that the approach can be used to generate a wide range of HCN solvated ions such as F Ϫ (HCN), Cl Ϫ (HCN), CN Ϫ (HCN), PhNO 2 ·Ϫ (HCN), Me 3 SiO Ϫ (HCN),and PhSiF 4 Ϫ (HCN), many of which are otherwise difficult to generate. The bond dissociation energy of CN Ϫ (HCN), generated by using this approach, has been measured by using energy-resolved collision-induced issociation (CID) to be 0. [2,3] in both the condensed phase and the gas phase. Whereas solvated halide [4,5] and alkoxide [6] ions are readily examined, clusters of cyanide are especially of interest because CN Ϫ is a pseudohalide with an ambidentate nature. Moreover, the conjugate acid, HCN, is a weak acid (⌬H acid ϭ 350.9 Ϯ 0.2 kcal/mol) [7] with extensive positive charge character on the hydrogen, making it an attractive hydrogen-bonding moiety in the gas phase [8]. Recently, HCN has gained much interest as it has been found to be a tracer for young stellar objects, and it has been detected in the atmosphere of Titan [9].An important challenge in carrying out studies involving cyanide or hydrogen cyanide is in the safe generation of the reagents. Because of its toxicity, HCN is rarely used directly as a reagent gas. Previous studies by Larson and McMahon [8] and Meot-Ner and coworkers [10] have used the solution phase reaction of KCN and acids (HCl or H 2 SO 4 ) to produce HCN, which was directly added to the mass spectrometer. Subsequently, ion-exchange equilibria [8] and van't Hoff measurements [10] were used to determine anion-neutral binding energies of CN Ϫ and HCN containing clusters. Recent studies have utilized the reaction of CH 4 and NH 3 with Pt catalyst to generate HCN in a molecular beam apparatus [11].In this work, we describe a simple in situ approach for generation of HCN for ion clustering studies. Hydrogen cyanide is formed by the neutral-neutral reaction of trimethylsilyl cyanide, Me 3 SiCN, with water in a flowing afterglow reactor. We demonstrate that the approach can be used to generate a wide range of HCN solvated ions and report energy-resolved CID studies of the HC 2 N 2 Ϫ ion formed. From these CID studies, we report a direct measurement of the [CN-HCN] Ϫ bond dissociation energy. Throughout this paper, HC 2 N 2 Ϫ refers to the m/z 53 species that has been observed and characterized. However, this notation does not indicate a specific ion structure. The structures of the HC 2 N 2 Ϫ isomers are addressed computationally at the end of this study. ExperimentalAll experiments were carried out in a flowing afterglow triple quadrupole mass spectrometer that has been previously described [12,13]. Fluoride was prepared by 70 eV electron ionization of neutral fluorine gas (5% in He, Spectra Gases Inc., Branchburg, NJ) and carried by helium buffer gas (0.400 torr, flow (He) ϭ 190 STP cm 3 /s) through the flow tube wh...

The reaction of Z,E,Z-PhSN=C(Ar)N=NC(Ar)=NSPh (Ar = 4-CH3C6H4) (1a) with MCPBA results in ring closure via an intramolecular redox process to give the 1,2,3,5-thiatriazole [Formula: see text] (4). An X-ray structural determination revealed that 4 contains a planar five-membered CNS(VI)NN ring with d(N—N) = 1.402(6) Å. The reaction of ArCN2(SiMe3)3 (Ar = 4-CH3C6H4) with one equivalent of MeSO2Cl, followed by two equivalents of PhSeCl, produces the sulfonyl-containing diazene MeSO2N=C(Ar)N=N(Ar)C=NSO2Me (11), which was shown by X-ray crystallography to adopt a Z,E,Z geometry. By contrast, the reaction of ArCN2(SiMe3)3 with one equivalent of ArS(O)Cl, followed by two equivalents of PhSeCl, yielded the sulfur(II)-containing diazene Z,E,Z-ArSN=C(Ar)N=NC(Ar)=NSAr (Ar = 4-CH3C6H4) (1b). Keywords: thiatriazoles, sulfonyl diazenes, intramolecular redox cyclization.