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.

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