Experiments have been carried out in which electrospray ionization has been used to generate ionic complexes of all-cis 1,2,3,4,5,6 hexafluorocyclohexane. These complexes were subsequently mass isolated in a quadrupole ion trap mass spectrometer and then irradiated by the tunable infrared output of a free electron laser in the 800-1600 cm(-1) range. From the frequency dependence of the fragmentation of the complexes, vibrational signatures of the complexes were obtained. Computational work carried out in parallel reveals that the complexes formed are very strongly bound and are among the most strongly bound complexes of Na(+) and Cl(-) ever observed with molecular species. The dipole moment calculated for the heaxafluorocyclohexane is very large (∼7 D), and it appears that the bonding in each of the complexes has a significant electrostatic contribution.

The structures and dissociation pathways of the proton-bound 3-cyanophenylalanine·trimethylamine cluster have been studied using a combination of infrared multiple photon dissociation (IRMPD) spectroscopy and density functional theory calculations. Three isomer motifs are identified: charge-solvated, zwitterionic, and trimethylamine (TMA)-bridged. While the TMA-bridged structures fragment to yield protonated TMA (channel 1) and protonated 3-cyanophenylalanine (channel 2), charge-solvated species exclusively fragment via channel 1 and zwitterionic species exclusively fragment via channel 2. Mechanisms are proposed.

The gas-phase structures of two halide-bound phenylalanine anions (PheX(-), X = Cl(-) or Br(-)) and five fluorinated derivatives have been identified using infrared multiple photon dissociation (IRMPD) spectroscopy. The addition of electron-withdrawing groups to the aromatic ring creates a π-acidic system that additionally stabilizes the halide above the ring face. Detailed ion structures were determined by comparing the IRMPD spectra with harmonic and anharmonic infrared spectra computed using B3LYP/6-311++G(d,p) as well as with 298 K enthalpies and Gibbs energies determined by the MP2(full)/6-311++G(2d,2p)//B3LYP/6-311++G(d,p) and MP2(full)/aug-cc-pVTZ//B3LYP/6-311++G(d,p) methods. PheX(-) structures were found to be dependent on both the nature of the anion and the extent of ring fluorination. Canonical isomers were established to be the dominant structures in every case, but halide addition significantly narrowed the energy gap with zwitterionic potential energy surfaces. This enabled zwitterions to appear as minor contributors to the gas-phase populations of Phe35F2Cl(-) and PheF5Br(-).

A combination of infrared multiple photon dissociation (IRMPD) spectroscopy and density functional theory calculations have been employed to study the structures and mode-specific dissociation pathways of the proton-bound dimer of 3-trifluoromethylphenylalanine (3-CF3-Phe) and trimethylamine (TMA). Three structural motifs are identified: canonical (charge-solvated), zwitterionic (charge-separated), and TMA-bridged. In the 1000-1350 cm(-1) region, similar spectra are observed in the TMA·H(+) and 3-CF3-Phe·H(+) product channels. At wavenumbers above 1350 cm(-1), infrared excitation of charge-solvated structures leads exclusively to production of protonated TMA, while excitation of zwitterionic or TMA-bridged structures results exclusively in production of protonated 3-CF3-Phe. The cluster potential energy landscape is topologically mapped and mechanisms for isomerization and mode-selective dissociation are proposed. In particular, cluster transparency as a result of IR-induced isomerization is implicated in deactivation of some IRMPD channels.

Clusters of all-cis 1,2,3,4,5,6-hexafluorocyclohexane and the dodecafluorododecaboron dianion, [CFH][BF] (n = 0-4), are investigated in a combined experimental and computational study. DFT calculations and IRMPD spectra in the region of 800-2000 cm indicate that CHF binds to open trigonal faces of BF via a three-point interlocking binding motif. Calculated binding interactions reveal substantial contributions from C-H···F hydrogen bonding and binding energies that are among the strongest observed for a neutral-anion system.

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Hypercoordinated complexes involving tricarbastannatrane cation [N(CHCHCH)Sn] with various Lewis bases are investigated in the gas and solution phases using a combination of infrared multiple photon dissociation (IRMPD) spectroscopy, NMR spectroscopy, and density functional theory calculations. Coordination is found to occur at the apical position leading to a pentacoordinated Sn center. Strongly electron donating Lewis bases disrupt the N···Sn transannular interaction and induce higher degrees of geometric distortion at the metal center than weakly donating Lewis bases, an effect that manifests as anharmonic shifts in the vibrational spectra. Once characterized in the gas phase, [N(CHCHCH)Sn(Lewis base)] structures were embedded in a dichloroethane polarizable continuum model to investigate solution phase properties. Calculated Sn NMR chemical shifts were found to be in good agreement with those measured experimentally, thus suggesting that the bonding properties of [N(CHCHCH)Sn] are essentially the same in the gas and solution phases.

The structures and properties of a series of phenylalanine (Phe) derivatives have been investigated in a joint computational and experimental infrared multiple photon dissociation (IRMPD) study. IRMPD spectra in the 1000-2000 cm region show that protonation is localized on the amine group in all cases. Intramolecular cation-π interactions between the ammonium group and the phenyl ring heavily influence molecular geometries and properties such as gas phase basicity and proton affinity. By varying substituents on the phenyl ring, one can sensitively tune the cation-π interaction and, therefore, the molecular structure and properties. Variations in molecular structures and properties as a function of phenyl ring substitution are shown to correlate with substituent Hammett parameters.