Reactions of Hf, Ta, and W with O2 and CO: Metal carbide and metal oxide cation bond energies

The reactions of Hf⁺, Ta⁺, and W⁺ with O₂ and CO are studied as a function of translational energy in a guided ion beam tandem mass spectrometer. All three reactions with O₂ form diatomic metal oxide cations in exothermic reactions that occur at the collision rate. In the CO systems, formation of both diatomic metal oxide and metal carbide cations is observed to be endothermic. The energy-dependent cross sections in the latter systems are interpreted to give 0 K bond energies (in eV) of D₀(HfC⁺) = 3.19 ± 0.03, D₀(TaC⁺) = 3.79 ± 0.04, D₀(WC⁺) = 4.76 ± 0.09, D₀(HfO⁺) = 6.91 ± 0.11, D₀(TaO⁺) = 7.10 ± 0.12, and D₀(WO⁺) = 6.77 ± 0.07. The present experimental values for TaO⁺ and WC⁺ agree well with literature thermochemistry, those for HfO⁺ and WO⁺ refine the available literature bond energies, and those for HfC⁺ and TaC⁺ are the first measurements available. The nature of the bonding in MO⁺ and MC⁺ is discussed and compared for these three metal ions and analyzed using theoretical calculations at a B3LYP/HW+/6-311+G(3df) level of theory. Bond energies for all MO⁺ and MC⁺ species are calculated using geometries calculated at this level and single point energies determined at B3LYP, CCSD, CCSD(T), QCISD, and QCISD(T) levels of theory with the same basis set. Reasonable agreement between the theoretical and experimental bond energies for the three metal oxide and three metal carbide cations is found. Potential energy surfaces for reaction of the metal cations with CO are also calculated at the B3LYP level of theory and reveal additional information about the reaction mechanisms.     

Electronic structure of NH+: An ab initio study

We report ab initio self‐consistent field MRSD‐CI electronic structure calculations of the NH⁺ cation. A basis set of DZ + POL quality augmented with Rydberg and bond functions was employed together with an extensive treatment of electron correlation. More than 50 electronic states of NH⁺ are reported, including doublets, quartets, and sextets. Leading configurations, vertical ionization energies of NH, vertical excitation energies of NH⁺, and potential energy curves are reported. Spectroscopic properties calculated for the known bound electronic states of NH⁺ are found in good agreement with experiment. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Hydrogen‐Atom Abstraction from Methane by Stoichiometric Vanadium–Silicon Heteronuclear Oxide Cluster Cations

Vanadium–silicon heteronuclear oxide cluster cations were prepared by laser ablation of a V/Si mixed sample in an O₂ background. Reactions of the heteronuclear oxide cations with methane in a fast‐flow reactor were studied with a time‐of‐flight (TOF) mass spectrometer to detect the cluster distribution before and after the reactions. Hydrogen abstraction reactions were identified over stoichiometric cluster cations [(V₂O₅)_n(SiO₂)_m]⁺ (n=1, m=1–4; n=2, m=1), and the estimated first‐order rate constants for the reactions were close to that of the homonuclear oxide cluster V₄O₁₀⁺ with methane. Density functional calculations were performed to study the structural, bonding, electronic, and reactivity properties of these stoichiometric oxide clusters. Terminal‐oxygen‐centered radicals (O_t ^. ) were found in all of the stable isomers. These O_t ^. radicals are active sites of the clusters in reaction with CH₄. The O_t ^. radicals in [V₂O₅(SiO₂)_1–4]⁺ clusters are bonded with Si rather than V atoms. All the hydrogen abstraction reactions are favorable both thermodynamically and kinetically. This work reveals the unique properties of metal/nonmetal heteronuclear oxide clusters, and may provide new insights into CH₄ activation on silica‐supported vanadium oxide catalysts.     

CAS SCF/CI calculations of potential energy surfaces of He3+ and He2+

Complete active space MC SCF (CAS SCF) calculations followed by second-order configuration interaction (SOCI) calculations are carried out on the potential energy surfaces (bending surface, linear surfaces) of the ²Σ_g⁺ ground state of He₃⁺. The potential minimum for the ²Σ_g⁺ state occurs at a linear geometry with HeHe bond length of 1.248 Å. The binding energy of He₃⁺ with respect to He + He⁺ + He was calculated to be 2.47 eV at the SOCI level. The energy required to dissociate He₃⁺ (²Σ_g⁺) into He₂⁺ (²Σ_u⁺) and He(¹S) is calculated to be 0.14 eV. The same level of SOCI calculations of He₂⁺ yield a D_e value of 2.36 eV.     

Theoretical prediction on HAlS+ and HSAl+ cations using multiconfiguration second‐order perturbation theory

Some low‐lying states of the HAlS⁺ and HSAl⁺ cations have been studied for the first time by large‐scale theoretical calculations using three methods: complete active space self‐consistent field (CASSCF), complete active second‐order perturbation theory (CASPT2), and density functional theory Becke's three‐parameter hybrid function with the nonlocal correlation of Lee–Yang–Parr (B3LYP) with the contracted atomic natural orbital (ANO‐L) and cc‐pVTZ basis sets. The geometries of all stationary points along the potential energy surfaces (PESs) were optimized at the CASSCF/ANO‐L and B3LYP/cc‐pVTZ levels. The ground and the first excited states of linear HAlS⁺ are predicted to be X²Π and A²Σ⁺ states, respectively. For the linear HSAl⁺ structure, the first excited state is A²Σ⁺. The X²Π state of linear HSAl⁺ is a second‐order saddle point, because it has two imaginary frequencies. Two bent global minima M1 and M2 were found along the 1²A′ and 1²A″ PESs, respectively. The CASPT2/ANO‐L potential energy curves of isomerization reactions were calculated as a function of HAlS bond angle. According to our calculations, the ground‐state HAlS⁺ is linear, whereas the ground‐state HSAl⁺ is bent. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Theoretical and experimental study of montmorillonite intercalated with tetramethylammonium cation

Structural and vibrational features of Na-montmorillonite and montmorillonite intercalated with tetramethylammonium cation (TMA⁺) were characterized theoretically and experimentally. Theoretical study was performed using density functional theory with inclusion of dispersion corrections. The analysis of the hydrogen bonds in the calculated models has shown that the Na⁺ cations coordinated by six water molecules (Na-M model) are bound to montmorillonite layers by moderate hydrogen bonds between water molecules and basal oxygen atoms of the tetrahedral sheets. Hydrated Na⁺ cations are stabilized by relatively strong hydrogen bonds among water molecules. In the intercalate model, the TMA⁺ cation is fixed in the interlayer space by weak hydrogen bonds between the methyl groups and basal oxygen atoms of montmorillonite layers. The calculated vibrational spectra are in a good agreement with the measured infrared spectra. The detailed analysis of the simulated vibrational spectra allowed unambiguous identification of corresponding bands in the measured spectra and their assignment to the particular vibrational modes. For example, calculations clearly distinguished between AlMgOH and AlAlOH stretching vibrations and also between the coupled vibrations of the methyl groups of the TMA⁺ cations.     

Thermal Conversion of Methane to Formaldehyde Promoted by Gold in AuNbO3+ Cluster Cations

In addition to generation of a methyl radical, formation of a formaldehyde molecule was observed in the thermal reaction of methane with AuNbO₃⁺ heteronuclear oxide cluster cations. The clusters were prepared by laser ablation and mass‐selected to react with CH₄ in an ion‐trap reactor under thermal collision conditions. The reaction was studied by mass spectrometry and DFT calculations. The latter indicated that the gold atom promotes formaldehyde formation through transformation of an Au?O bond into an Au?Nb bond during the reaction.     

Mean amplitudes of vibration of the XF+4 interhalogen cations

Mean amplitudes of vibration for the cations ClF⁺₄, BrF⁺₄ and IF⁺₄ have been calculated using the ‘Method of the Characteristic Vibrations’ and recently revised spectroscopic data. The results are briefly discussed and some comparisons with isoelectronic molecules and other related species are made.     

Photochemistry of trimethylene oxide and trimethylene sulfide radical cations in freonic matrices at 77 K

It was shown that trimethylene oxide (oxetane) radical cations were converted at 77 K into either distonic radical cations ·CH₂CH₂CH=OH⁺ or 2-oxetanyl radicals, depending on the freonic matrix used, by the action of light at λ = 546 nm and trimethylene sulfide radical cations transformed into distonic radical cations CH₂CHSH⁺CH ₂ ^· under 436-nm irradiation. The quantum yields of the photochemical reactions were determined. Quantum-chemical calculations on the structure and HFC constants of the radical cations and possible paramagnetic products of their transformation were performed. The reasons behind the observed difference in reactivity between the radical cations under the action of light are discussed.     

Mobility of water molecules in Li+, Na+ and Cs+ ionic forms of Nafion membrane studied by NMR

Correlation times and diffusion coefficients of water molecules were measured for the first time by ¹H spin relaxation and pulsed field gradient NMR in Li⁺, Na⁺ and Cs⁺ ionic forms of Nafion 117 membrane. Hydration numbers of Li⁺, Na⁺ and Cs⁺ cations were calculated. It was shown that at high humidity macroscopic transfer is controlled by the local translational motion of water molecules.     

Solvation of Metal Cations in Non-aqueous Liquids

The role that alkali cations in non-aqueous solvents play in organic reactions continues to be a topic of interest. In particular it has been observed that these cations can alter the stereoselectivity of organic reactions. Our interest is to first understand the nature of cation–ether complexes, then to investigate the role that the cation plays in the reaction. We have used the electronic structure techniques Hartree-Fock (HF), Second-order Møller-Plesset perturbation theory (MP2), and the Becke three-parameter exchange functional coupled with the nonlocal correlation functional of Lee, Yang, and Parr (B3LYP) to study the structure and properties of tetrahydrofuran (THF) and dimethyl ether (DME) solvation complexes with Li⁺, Na⁺, K⁺, Cu⁺, and MgCl⁺. The values calculated for DME complexes were compared with existing experimentally determined data. The B3LYP/6-31⁺G^? model chemistry was found to be the most accurate and efficient method of modeling the cation–DME molecular system. The energetic trends observed in the DME results were also observed in the THF data. Based on the accuracy of the calculations and the computational cost of the calculations, B3LYP was found to be the most desirable method of modeling these types of systems.     

Ionic Solvation in formic acid,MO SCF calculations on solvated univalent ions

CNDO/2 calculations have been performed for the mono-, di- and tetra-solvates of Li⁺, Na⁺ and Cl^? with formic acid. The most stable position for the cations is found to be between the CH hydrogen and carbonyl oxygen, confirming similar conclusions from experimental results. The calculated changes in electron densities agree well with observations in ¹H-NMR spectra.Calculated solvation energies are found to show the right relative order for the cations, although absolute values are too high. For the anion, also the absolute value is in reasonable agreement with experiment. CNDO minimum geometries, charge distributions and bond indices are given for all solvates and discussed in respect to possible methodical errors.     

CH2 + transfer to pyridine nucleophiles: a means of producing α-distonic ions

The distonic radical cation C₅H₅N⁺?^·CH₂ can be generated by the reactions of neutral pyridine with the radical cations of cyclopropane, ethylene oxide, and ketene, as well as with the [C₃H₆]⁺ ion from fragmentation of tetrahydrofuran. The distonic product ion can be distinguished from isomeric methylpyridine radical cations because the former gives characteristic [M?CH₂]⁺, [M ? CH₂NCH]⁺, and a doubly charged ion, all of which are produced on collisional activation. Furthermore, the distonic species completely transfers CH₂ ⁺ to more nucleophilic, substituted pyridines. These properties are all consistent with the assigned distonic structure. Another distonic isomer, the (3-methylene) pyridinium ion, can be distinguished from the (1-methylene)pyridinium ion on the basis of their different fragmentation behaviors. The latter ion exhibits higher stability (lower reactivity) than the prototypal [·CH₂NH₃ ⁺], making available a distonic species whose bimolecular reactivity can be readily investigated.     

Coordination polyhedra of hydration shells of Na+ and K+ cations in aqueous solutions

Simulation of the hydration of Na⁺ and K⁺ cations in dilute solution was performed by the Monte Carlo method. A novel approach to structural analysis of hydration shells of ions was developed. Specific sets of coordination polyhedra formed by water molecules of the first coordination sphere were found. Structural and energy characteristics of hydration were calculated. The effect of Na⁺ and K⁺ cations on the structure of the network of H-bonds and mobility of water molecules in hydration shells was studied. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 852–857, May, 1999.     

Infrared Spectrum of the Adamantane+–Water Cation: Hydration‐Induced C−H Bond Activation and Free Internal Water Rotation

Diamondoid cations are reactive intermediates in their functionalization reactions in polar solution. Hydration is predicted to strongly activate their C?H bonds in initial proton abstraction reactions. To study the effects of microhydration on the properties of diamondoid cations, we characterize herein the prototypical monohydrated adamantane cation (C₁₀H₁₆⁺–H₂O, Ad⁺–W) in its ground electronic state by infrared photodissociation spectroscopy in the CH and OH stretch ranges and dispersion‐corrected density functional theory (DFT) calculations. The water (W) ligand binds to the acidic CH group of Jahn–Teller distorted Ad⁺ via a strong CH???O ionic H‐bond supported by charge–dipole forces. Although W further enhances the acidity of this CH group along with a proton shift toward the solvent, the proton remains with Ad⁺ in the monohydrate. We infer essentially free internal W rotation from rotational fine structure of the ν₃ band of W, resulting from weak angular anisotropy of the Ad⁺–W potential.     

Sorption of Cs<Superscript>+</Superscript> and Sr<Superscript>2+</Superscript> by ion exchanger based on titanium phosphate

Sorption capacity of a composite ion exchanger based on titanium phosphate for Cs⁺ and Sr²⁺ cations was studied. The effect of pH and concentration of salts and, in particular, sodium chloride in solution on the sorption efficiency and distribution coefficient was analyzed. The diffusion coefficients were calculated for the Cs⁺ and Sr²⁺ cations and the time of half-exchange of the Na⁺ cation for the Cs⁺ and Sr²⁺ cations was found.     

Rates of radiative recombination to form HD+ and HeH+

The rates of radiative recombination to form HD⁺ and HeH⁺ along the ground electronic state potential surface have been calculated from known potentials. These exact quantum calculations are compared with a classical model. For the formation HD⁺, the classical model predicts the rate in the range of 100–1000 K. Below 100 K, the rate is dominated by the effect of low energy shape resonances. For the formation of HeH⁺, the classical model predicts the correct temperature dependence.     

Theoretical study on conformational features and cation-binding properties of a diquinone calix[4]arene

Theoretical studies of a diquinone calix[4]arene and its interactions with the cations Li⁺, Na⁺, K⁺ and Ag⁺ have been performed. Conformational features and cation-binding properties were evaluated with the restricted hybrid Becke three-parameter exchange functional method using the 6-31G(d) basis set and its relativistic effective core potentials. To model the effect of medium, the polarisable continuum model was also used. Four typical conformations of the parent diquinone calix[4]arene were studied. The calculated results show that the most stable conformers are 1,3-alternate and partial cone in the gas phase and in CH₂Cl₂ solution, respectively. The optimised geometric structures were used to perform natural bond orbital analysis. The two main types of driving force metal–ligand and cation–π interactions are investigated. The calculated binding energy for cations (Li⁺, Na⁺, K⁺ and Ag⁺) is discussed. The calculated results indicate that cone complexes are the most stable.     

A CNDO/2 study of the structure and relative stability of the HCS+-CSH+ system

The structure and relative stability of the HCS⁺-CSH⁺ system are calculated by the CNDO/2 method, and the results are compared with those of ab initio SCF calculations. Good agreement is observed.     

Sulfonamide and Morpholine‐Based Dual Chemosensor for Cu2+ and Ag+ in Different Solvent Media

The detection of cations has attracted considerable interest because of their importance in various physiological processes. In this study, compound 1 bearing sulfonamide and morpholine functionalities was synthesized. Its structure was well characterized by NMR spectroscopy and mass spectrometry. UV/vis absorption spectra and fluorescence spectra indicated that it displayed high sensitivity and selectivity for Cu²⁺ and Ag⁺ by switching solvent media. It means that: (1) it showed selective response to Cu²⁺ in acetonitrile, (2) whereas it exhibited high selectivity for Ag⁺ in water. The density functional theory calculations were used to clearly explain the different recognition behaviors in different solvent media. This research suggests that compound 1 bearing sulfonamide and morpholine functionalities could act as a multifunctional chemosensor for monitoring multiple cations by changing solvent media and provides an alternative approach to design novel dual cations chemosensors.