Reaction mechanism of platinum dimer cation with ammonia based on the relativistic density functional study

The gas‐phase reactions between Pt and NH₃ have been investigated using the relativistic density functional approach (ZORA‐PW91/TZ2P). The quartet and doublet potential energy surfaces of Pt + NH₃ have been explored. The minimum energy reaction path proceeds through the following steps: Pt(⁴Σ_u) + NH₃ → q‐1 → d‐2 → d‐3 → d‐4 → d‐Pt₂NH⁺ + H₂. In the whole reaction pathway, the step of d‐2 → d‐3 is the rate‐determining step with a energy barrier of 36.1 kcal/mol, and exoergicity of the whole reaction is 12.0 kcal/mol. When Pt₂NH⁺ reacts with NH₃ again, there are two rival reaction paths in the doublet state. One is degradation of NH and another is loss of H₂. In the case of degradation of NH, the activation energy is only 3.4 kcal/mol, and the overall reaction is exothermic by 8.9 kcal/mol. Thus, this reaction is favored both thermodynamically and kinetically. However, in the case of loss of H₂, the rate‐determining step's energy barrier is 64.3 kcal/mol and the overall reaction is endothermic by 8.5 kcal/mol, so it is difficult to take place. Predicted relative energies and barriers along the suggested reaction paths are in reasonable agreement with experimental observations. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Ab initio study of the reaction of CHO+ with H2O and NH3

An MP4(full,SDTQ)/6-311++G(d,p)//MP2(full)/6-311++G(d,p) ab initio study was performed of the reactions of formyl and isoformyl cations with H₂O and NH₃, which play an important role in flame and interstellar chemistries. Two different confluent channels were located leading to CO+H₃O⁺/NH. The first one corresponds to the approach of the neutral molecule to the carbon atom of the cations. The second one leads to the direct proton transfer from the cations to the neutrals. At 900 K the separate products CO+H₃O⁺/NH are the most stable species along the Gibbs energy profiles for the processes. For the reaction with H₂O the reaction channel leading to HC(OH) (protonated formic acid) is disfavored with respect to the two CO+H₃O⁺ channels in agreement with the experimental evidence that H₃O⁺ is the major ion observed in hydrocarbon flames. According to our calculations, NH+H₂O are considerably more stable in Gibbs energy than NH₃+H₃O⁺;NH will predominate in the reaction zone when ammonia is added to CH₄+Ar diffusion flame, as experimentally observed. At 100 K the most stable structures are the intermediate complexes CO…HOH/HNH. Particularly the CO…HOH complex has a lifetime large enough to be detected and, therefore, could play a certain role in interstellar chemistry. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 1432–1443, 1999     

Theoretical study of one‐electron bonds in a series of high‐spin lithium–beryllium–hydrogen clusters: “Valence shell single‐electron repulsion” rule and electron localization function analysis

A series of high‐spin clusters containing Li, H, and Be in which the valence shell molecular orbitals (MOs) are occupied by a single electron has been characterized using ab initio and density functional theory (DFT) calculations. A first type (⁵Li₂, ⁿ⁺¹LiH_n+ (n = 2–5), ⁸Li₂H) possesses only one electron pair in the lowest MO, with bond energies of ～3 kcal/mol. In a second type, all the MOs are singly occupied, which results in highly excited species that nevertheless constitute a marked minimum on their potential energy surface (PES). Thus, it is possible to design a larger panel of structures (⁸LiBe, ⁷Li₂, ⁸Li, ⁴LiH⁺, ⁶BeH, ⁿ⁺³LiH (n = 3, 4), ⁿ⁺²LiH (n = 4–6), ⁸Li₂H, ⁹Li₂H, ²²Li₃Be₃ and ²²Li₆H), single‐electron equivalent to doublet “classical” molecules ranging from CO to C₆H₆. The geometrical structure is studied in relation to the valence shell single‐electron repulsion (VSEPR) theory and the electron localization function (ELF) is analyzed, revealing a striking similarity with the corresponding structure having paired electrons. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

L'action de l'ammoniac sur l'oxyde cuivrique. et les hydroxo-complexes de cuivre (II)

Using a new mathematical treatment, the nature and stability constants of the simple and mixed complex-species of copper(II) with hydroxyde and ammonia as ligands have been determined. The solubility curves of CuO in heterogeneous equilibrium have been identified in function of pH only and in function of pH and pNH_3tot at 25° and unit ionic strength (NaClO₄). The predominent species in the relatively dilute system limited by the ionic strength are [Cu²⁺], [Cu(OH)₂], [Cu(OH)], [Cu(OH)], [Cu(NH₃)], [Cu(NH₃)], [Cu(NH₃)], [Cu(NH₃) (OH)⁺], [Cu(NH₃)₃(OH)⁺] and [Cu(NH₃)₂(OH)₂].     

Reorganization of highly preorganized hosts upon cation complexation: Ab initio study of fluorospherands

Fluorospherands (F‐spherands) are highly preorganized hosts composed of fluorobenzene or 4‐methylfluorobenzene units attached to one another at their 2,6‐positions. To understand the intrinsic factors affecting cation complexation, we investigated the complexation behavior between F‐spherands and cations using density functional theory (DFT) at the level of B3LYP/6‐31G**. The F6‐spherand (C₆H₃F)₆, ( 1 ) has a highly preorganized spherical cavity, which can encapsulate Li⁺ and Na⁺. Its cavity is not big enough for K⁺ and NH, which prefer external binding. Plausible conformations were studied for F8‐spherand (C₆H₃F)₈. Conformer of D_2d symmetry ( 2b ) is more stable than that of D_4d ( 2a ), in agreement with NMR experiments. The cavity size of F8‐spherand is big enough to encapsulate all cations studied. However, the cavity size of 2b is smaller than that of 2a , which resulted in the guest selectivity. Upon complexation, 2b conformation is more stable for Li⁺ and Na⁺, while 2a conformation is preferred for larger cations such as K⁺ and NH. Thus, the ab initio calculations over these highly preorganized fluorospherands give important insights into their host–guest chemistry. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Correlated n1,3S states for coulomb three‐body systems

n^1,3S (n = 1 ? 4) states for atomic three‐body systems are studied with the Angular Correlated Configuration Interaction method. A recently proposed angularly correlated basis set is used to construct, simultaneously and with a single diagonalization, ground and excited states wave functions which: (i) satisfy exactly Kato cusp conditions at the two‐body coalescence points; (ii) involve only linear parameters; (iii) show a fast convergency rate for the energy; and (iv) form an orthogonal set. The efficiency of the method is illustrated by the study a variety of three‐body atomic systems [m m m] with two negatively charged light particles, with diverse masses m and m, and a heavy positively charged nucleus m. The calculated ground 1¹S and excited n^1,3S (n = 2 ? 4) state energies are compared with those given in the literature, when available. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

L'action de l'ammoniac sur l'hydroxyde de cadmium et la stabilité des complexes en milieu aqueux

The solubility of precipitated Cd(OH)₂ was determined at 25°C in 1 M NaClO₄, as a function of pH and of the ammonia content of the solutions. Formation constants were obtained for the following hydroxo, ammine and hydroxo-ammine complexes: CdOH⁺, Cd(OH)₂, Cd(OH), CdNH, Cd(NH₃), Cd(NH₃), Cd(NH₃) and Cd(OH)₂NH₃. The solubility product of the hydroxide was also calculated. The presence of polynuclear species was investigated by titrimetric determinations of the hydrogen ion concentration at constant metal concentration.     

Probing the ultrafast photoelectron spectra of Br2 molecule

The time‐dependent‐wave‐packet method is applied to study the ionization of Br₂ molecule with four ionization processes. The ground state absorption makes the photoelectron to be left in the three final ionic states: Br (X²∑), Br (A²∏_u), and Br (B²∑), and each population of these ionic states is related with the laser intensities. The information of the dissociation can be got by analyzing the photoelectron features of the transient wave packet, which also suggests that an ionization process occurs during the dissociation, and the Br atoms that mainly resulted from the dissociation of Br₂ (C¹∏_u) are ionized at later time delays as the dissociation is nearly complete. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Capacitively coupled contactless conductivity detection with dual top–bottom cell configuration for microchip electrophoresis

An optimized capacitively coupled contactless conductivity detector for microchip electophoresis is presented. The detector consists of a pair of top–bottom excitation electrodes and a pair of pickup electrodes disposed onto a very thin plastic microfluidic chip. The detection cell formed by the electrodes is completely encased and shielded in a metal housing. These approaches allow for the enhancement of signal coupling and extraction from the detection cell that result in an improved signal‐to‐noise‐ratio and detection sensitivity. The improved detector performance is illustrated by the electrophoretic separation of six cations (NH, K⁺, Ca²⁺, Na⁺, Mg²⁺, Li⁺) with a detection limit of approximately 0.3 μM and the analysis of the anions (Br^?, Cl^?, NO, NO, SO, F^?) with a detection limit of about 0.15 μM. These LODs are significantly improved compared with previous reports using the conventional top–top electrode geometry. The developed system was applied to the analysis of ions in bottled drinking water samples.     

Adaptation of a proton transfer reaction mass spectrometer instrument to employ NO+ as reagent ion for the detection of 1,3‐butadiene in the ambient atmosphere

A proton transfer reaction mass spectrometer (PTR‐MS) instrument was adapted to employ NO⁺ as a chemical reagent ion without any hardware changes by switching the reagent ion source gas from water vapor to dry air. Ionization of dry air within the hollow cathode ion source generates a very intense source of NO⁺ with only a minor impurity of NO. The intensities of the primary NO⁺ reagent ion and the unwanted impurity NO are controllable and dependent on the operational conditions of the hollow cathode ion source. Ion source tuning parameters are described, which maintain an intense source of NO⁺ while keeping the impurity NO signal to less than 2% of the total reagent ion intensity. This method is applied to the detection of 1,3‐butadiene. NO⁺ reacts efficiently with 1,3‐butadiene via a charge exchange reaction to produce only the molecular ion, which is detected at m/z 54. Detection sensitivities of the order of 45 pptv for a 1‐s measurement of 1,3‐butadiene are demonstrated. We present the first real‐time on‐line sub parts per billion measurement of 1,3‐butadiene in the ambient atmosphere. The only likely interference is from 1,2‐butadiene. Concurrent measurements of benzene are provided and suggest that the vehicular emissions are the predominant source of 1,3‐butadiene in a suburban Boston area monitoring location. Copyright © 2009 John Wiley & Sons, Ltd.     

Sulfoximid und Sulfoximidium-Salze – Strukturen und H?Brückenbindungen

Sulfoximide and Sulfoximidium Salts – Structures and Hydrogen Bonding In the solid state dimethylsulfoximide ( 1 ) (orthorhombic; space group Pbca; a = 577.8, b = 931.2 and c = 1645.6 pm) makes intermolecular N? H ? N hydrogen bonds. The hydrogen halide salts (CH₃)₂S(O)NH₂⁺Hal^? (( 2 ), Hal^??Cl^?; ( 4 ), Hal^??Br^?) reacts with metal halides to yield (CH₃)₂S(O)NH₂⁺MHal with the complex anions (( 5 ), MHal?SbCl₄^?; ( 6 ), MHal?SbCl₅^2?; ( 7 ), MHal?SbCl₆^?; ( 8 ), MHal?SbBr₅^2?; ( 9 ), MHal?AlCl₄^?). 2 crystallizes from ethanol (96%) as [(CH₃)₂S(O)NH₂⁺Cl^?]₂ · H₂O ( 3 ). The structures of 3 (monoclinic; space group P2₁/c; a = 917.0, b = 1344.7, c = 1080.8 pm and β = 103.8°; Z = 10), 4 (orthorhombic; space group Pbcn; a = 1028.9, b = 1132.6, c = 1074.1 pm; Z = 8) and 6 (monoclinic; space group C2/c; a = 2041.1, b = 1101.4, c = 3365.6 pm and β = 153.8°; Z = 8) are determined by X-ray analysis. In 6 Sb is coordinated in a distorted octahedra by 6 Cl in three short (mean 245,5 pm; SbCl₃) and three long distances (291 to 299 pm; Cl^?). Two of the chloride ions connect the Sb atoms to infinite Sb …? Cl …? Sb chains. Except for 7 and 9 there are bridges between the NH₂ groups and the halide ions. The NH valence vibrations are discussed in view of hydrogen bonding.     

Theoretical study on the ion–molecule reaction of NH+ with CH2O

An in‐depth theoretical study is carried out at the B3LYP/6‐311G(d,p), M062X/aug‐cc‐pVDZ and CCSD(T)/6‐311++G(3df,2dp) (single‐point) levels as an attempt to explore the mechanism of the little‐understood ion–molecule reaction between NH⁺ and CH₂O. Various possible reaction pathways are taken into account. It is shown that six dissociation products, including P ₁ (²N + CH₂OH⁺), P ₂ (⁴N + CH₂OH⁺), P ₃ (³NH + CH₂O⁺), P ₄ (NH₂ + HCO⁺), P ₅ (NH + CO), and P ₉ (H + CONH) are all accessible both kinetically and thermodynamically. Among these products, P ₄ is the most competitive product with predominant abundance, and the second most feasible product is P ₃ , followed by P ₂ and P ₁ . The remaining products, P ₅ and P ₉ , may have negligible yield under room temperature condition. As the intermediates and transition states involved in the NH⁺ + CH ₂ O reaction all stay below the reactant, the title reaction is expected to be rapid, which is consistent with the measured large rate constant in experiment. The present study will enrich our knowledge of the chemistry of NH⁺. Furthermore, our calculated result is compared with the previous experimental research, and, meanwhile, it provides a useful guide for understanding analogous reaction, NH⁺ with CH₂NH. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

The generalized separated electron pair model. II. An application to NH,NH3, NH,NH2− and N3−

The Separated Electron Pair (SEP) model (Strongly Orthogonal Geminals) and methods for its systematic extension has been applied to the series: NH, NH₃, NH, NH^2? and N^3?. On going from NH to N^3?, the SEP model, in its most general form, recovers 85–75% of the intrapair correlation energy and 60–55% of the interpair correlation energy obtainable with the given basis set. The best wave functions for each species recovered about 45–50% of the total empirical correlation energy which is expected to be very close to the basis set limit. It was apparent that the SEP model yields a set of one-electron functions that are very useful for further improvement of the wave function. This fact apparently remains true even when the SEP model itself gives very poor energies.     

Charge stripping C

Measurements of the translational energy loss accompanying the charge-stripping reactions M⁺+N→M²⁺+N+e⁻ and M²⁺+N→M³⁺+N+e⁻ have been performed for C, C and C, C respectively. The energy nesessary to remove the second electron from Buckminsterfullerene was determined, Q=IE(C→C=12.25±0.5 eV.     

Hydration structures and energetics of phospholipid

Using previously reported ab initio potentials of the intermolecular interaction energies of phospholipid (PL), Lysophosphatidyl Ethanolamine, with one Na⁺ ion and one water molecule, we performed Monte Carlo simulations for PL-water and PL-Na⁺-water systems. Water-water and PL-water interaction energetics of PL hydration sites are analyzed to understand, in a qualitative way, why the PL head part shows hydrophilicity and the tail part shows hydrophobicity. The interaction of Na⁺ with PL, as well as the interaction of water with PL, is visualized from the analysis of the hydration structures near PL, and the radial distribution functions are analyzed for selected hydration sites. The PL molecule shows much stronger interaction with Na⁺ than with water. The Na⁺ ion is likely to be strongly bound to PO, even to the extent of being trapped, whereas, for water, there exist two strong binding regions near NH and PO. Three water molecules near NH are much more strongly bound than four water molecules near the double-bonded oxygens of PO. The hydrogens of CH₂ adjacent to NH show somewhat strong hydrophilicity, while the hydrogens of CH₂ adjacent to PO does not show such characteristics. The CH₂ groups at the PL tail part give repulsive interactions with water molecules, showing hydrophobicity. Water molecules near the PL tail are stabilized only by water-water interactions.     

Theoretical spectroscopic studies of InI and InI+

Relativistic configuration interaction calculations are carried out to study the electronic structure and spectroscopic properties of InI and InI⁺. Potential energy curves of the ground and a number of low‐lying states are constructed. Spectroscopic parameters of the bound states of both species are computed and compared with the experimental and other theoretical data. Effects of spin‐orbit coupling on the spectroscopic properties are studied. Because of the presence of the heavy atoms the effect is large. The spin‐orbit splitting of the ground state (X²Π) of InI⁺ is more than 8350 cm^?1. As a result of the strong spin‐orbit interaction between X²Π and A²Σ⁺ of InI⁺, the potential energy curve of A²Σ becomes repulsive. Radiative lifetimes for the spin‐forbidden transitions such as A³Π?X¹Σ and B³Π₁ ?X¹Σ of InI and spin‐allowed transitions such as B²Σ⁺?A²Σ⁺, C²Π?A²Σ⁺, and B²Σ⁺?X²Π are calculated. Vertical and adiabatic ionization energies of InI and the electric dipole moments of both the neutral and ionic species are estimated. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Ammonia chemical ionization mass spectrometry of alcohols: Structural,stereochemical, molecular-size and temperature effects

Ammonia chemical ionization (CI) mass spectra of various open-chain, cyclic and unsaturated C₅- to C₁₀-alcohols were obtained at source temperatures ranging from 60° to 250°C. The reactivity of the ammonia adduct ion MNH and its fragmentation channels are characteristic for substrate structure. Although strongly temperature-dependent, the spectra give nevertheless information on the OH-group environment as well as on the C-skeleton at any source temperature. Primary, secondary and tertiary alcohols as well as allylic and simple olefinic alcohols can be distinguished by their spectra, which show ammonium adduct ions [MNH₄]⁺, adduct dehydrogenation ions [MNH₄-H₂], ammonium substitution ions [MNH₄-H₂O]⁺ and [M-OH]⁺-ions as the main characteristic peaks. Moreover, konfigurational assignments of stereoisomeric alcohols are possible for larger substrate-size and source-temperature ranges than with isobutane CI mass spectrometry. Homologous M NH-ions show molecular-size control of fragmentation and linear MNH-ions are less stable than branched isomers due to incomplete energy randomization.     

Maximum carbonyl‐coordination number of scandium Computational study of Sc(CO)n (n = 1–7), Sc(CO)7− and Sc(CO)63−

Understanding the maximum bonding ability is very important with the potential both to design new compounds and to broaden chemists' imagination. While the coordination ability of the late transition metals has been richly understood, that of scandium is very poor. In this work, a detailed computational study on the equilibrium geometries, stability and vibrational frequencies of a series of Sc(CO)_n (n = 1–7), Sc(CO) and Sc(CO) is reported using density functional theory functionals and the coupled cluster (single‐point) method with 6‐311+G(3df) basis set. It was shown that the obtained sequential and average CO binding energies of Sc(CO)_n (n = 4–7), Sc(CO) and Sc(CO) are comparable to those of the experimentally known species, i.e., smaller Sc‐carbonyls (n ≤3) and the analog Ti(CO)₇⁺. Thus, the studied high scandium carbonyls could all be experimentally accessible. In addition, the studied Sc(CO)_n generally favor the low‐spin ground state (doublet) structures except ScCO and Sc(CO)₃ that are in the quartet states. The previously uncertain spectrum bands were assigned to Sc(CO)₄ and Sc(CO)₅ in this work. In all, the appreciable stability suggested that the last 18‐electron first‐row transition metal carbonyls, that is, Sc(CO) and Sc(CO), could be accessible in experiment. © 2013 Wiley Periodicals, Inc.     

Integral Hellmann-Feynman computations on H3ABHn—H2ABHn+1 rearrangements

Extensively optimized Lewis orbital (Frost model) structures are reported for CH₃N, CH₃NH⁺, CH₃CH, CH₃CH, CH₃BH₂, CH₂NH, and CH₂NH (spiro and planar). Electronic energy differences between these isoelectronic species were estimated by the integral Hellmann-Feynman (iHF ) formula, with the hope that satisfaction of the Hellmann-Feynman conditions would lead to accurate iHF values of energy changes. We observed a strongly nonlinear relation between the iHF error and the departure of the overlap of wave-functions of the structures from unity. MO computations in common orbital (not determinantal) basis sets for CH₃NH⁺? CH₂NH (planar), CH₃N? CH₂NH, and CH₃CH? CH₂CH₂ produced greatly improved iHF estimates of energy changes, reducing errors by as much as 80 times. Certain features of the static optimum structures and the transition densities suggested that the syn path for rearrangement of methyl carbene to ethylene is a general feature of rearrangements in these systems.