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     

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.     

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].     

Thermische Zersetzung und Lösungskalorimetrie von Ammoniumsamariumbromiden

Thermal Decomposition and Solution Calorimetry of Ammonium Samarium Bromides The ternary pure phases on the line SmBr₃—NH₄Br in the thermodynamically equilibrium have been synthesized by solid state reactions and characterized by X‐ray powderdiffraction. The existence of a new phase (NH₄)₃SmBr₆ was demonstrated beside the known phases (NH₄)₂SmBr₅ and NH₄Sm₂Br₇. The decomposition equilibria of the ammonium samarium bromides have been investigated by total pressure measurements and the thermodynamical data of the solid phase complexes derived from the decompostion functions. The standard enthalpies of solution in 4n HBr (aq.) of the ternary phases, SmBr₃ and Sm₂O₃, were measured and on the basis of these values and known data the standard enthalpies of ammonium samarium bromides were derived. The phase diagram is constructed on the basis of DTA measurements. Data from total pressure measurements: ΔH((NH₄)₃SmBr_{6, f, 298}) = —400, 0 ± 6, 5 kcal/mol S°((NH₄)₃SmBr_{6, f, 298}) = 146, 9 ± 8 cal/K · mol ΔH((NH₄)₂SmBr_{5, f, 298}) = —340, 6 ± 5, 0 kcal/mol S°((NH₄)₂SmBr_{5, f, 298}) = 106, 0 ± 6 cal/K · mol Δ(NH₄Sm₂Br_{7, f, 298}) = —479, 4 ± 6, 0 kcal/mol S°(NH₄Sm₂Br_{7, f, 298}) = 119, 5 ± 7 cal/K · mol Data from solution calorimetry: ΔH(SmBr_{3, f, 298}) = —204, 4 ± 1, 8 kcal/mol ΔH((NH₄)₃SmBr_{6, f, 298}) = —400, 7 ± 3, 2 kcal/mol ΔH((NH₄)₂SmBr_{5, f, 298}) = —339, 6 ± 2, 6 kcal/mol ΔH(NH₄Sm₂Br_{7, f, 298}) = —475, 6 ± 4, 4 kcal/mol     

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     

Synthesis,Crystal Structure,and IR Investigations of [(NH3)5V?O?V(NH3)5]I4 · NH3 and [(NH3)5Ti?O?Ti(NH3)5]I4 · NH3

The reaction of VI₂ or TiI₃, respectively, with ammonia in the presence of traces of water or oxygen, respectively, leads to [(NH₃)₅M? O? M(NH₃)₅]I₄ · NH₃ with M = V, Ti. Their structures were solved by X-ray single crystal data: Pbca (No. 61), Z = 4, M = V: a = 12.482(4) Å, b = 14.819(6) Å, c = 13.286(5) Å, N(F ? 3σF) = 983, N(variables) = 88, R/R_w = 0.053/0.063, M = Ti: a = 12.628(4) Å, b = 14.970(4) Å, c = 13.359(3) Å, N(F ? 3σF) = 1188, N(variables) = 88, R/R_w = 0.043/0.047. The structures consist of corner sharing octahedra double units [(NH₃)₅M? O? M(NH₃)₅]⁴⁺ with eclipsed conformation which are stacked together according to the motif of a distorted cubic face centered arrangement for the bridging oxygen atoms. IR spectroscopic investigations of the undeuterated vanadium compound and of 5% deuterated samples hint to N? H … I hydrogen bridge bonds and to remarkable π-bonding between the transition metal and the bridging oxygen atoms.     

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.     

A theoretical approach to substituent effects. A comparison of the isoelectronic BH,CH3, and NH groups and their interaction with substituents in disubstituted benzenes

Ab initio molecular orbital theory with the STO -3G basis set is used to examine both charge and energy interactions in a series of meta- and para-substituted phenylborate anions and toluenes. Comparison of the results is made with data for substituted anilinium cations. It is concluded that whereas NH is a powerful σ acceptor, with essentially no π interaction, BH is primarily a π donor, and, to a slight extent only, a π donor. CH₃ is indicated to be both a weak σ and π donor. Energies of interaction of BH and NH with a series of substituents are an order of magnitude larger than corresponding values for CH₃. Interaction energies for BH are of opposite sign to those for NH. The results may be understood qualitatively using perturbation molecular orbital (PMO ) theory.     

Theoretical predictions of the structures and electronic spectra of C60NH with comparisons with the isoelectronic molecules C60O and C60CH2

Intermediate neglect of differential overlap (INDO ) calculations were used to study two structures of C₆₀NH: one of C_2ν, geometry with a bridging NH across the bond between two fused six-membered rings in C₆₀ and the other of C_s geometry with a bridging NH across the bond between a five- and a six-membered ring. We calculated the most stable isomer of C₆₀NH to be of C_2ν, symmetry. It was found that the C_2ν isomer has a protonated aziridine structure with a bridging C? C bond length of 0.1520 nm. The electronic spectra of both isomers of C₆₀NH were calculated. Comparisons were made with the isoelectronic molecules C₆₀O and C₆₀CH₂, cases in which the calculated electronic spectra for the most stable isomers C₆₀O (C_2ν) and C₆₀CH₂ (C_2ν) are in good agreement with recent experimental results. © 1995 John Wiley & Sons, Inc.     

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.     

Complexes of Silver(l) with arsenic and phosphorus donor ligands. Co-ordination number 4

Some tetracoordinated complexes having the formulae, [AgL₄]X (L = Triphenyl-arsine; X = NO, ClO and BrO) and [AgL₃X] (L = Triphenyl-arsine/phosphine; X = SCN^? and NCO^?) have been prepared and characterised by analyses, conductance, magnetic susceptibility and infra-red spectroscopy.     

Ab initio studies of negative ion-molecule(s) clusters present in the atmosphere. II. OH−(H2O)n for n = 0, 2, 3, 4

Ab initio calculations are performed with 6–31G basis set to study the geometry and binding of the H₃O, H₅O, H₇O, and H₉O complexes. The H₃O complex is also investigated with the 6–31 G* basis set and MP 2 (Moller–Plesset perturbation theory of second order).     

Synthesis and Crystal Structure of Tricaesium Heptaphosphide–Ammonia(1/3) Cs3P7·3 NH3

Recrystallization of Cs₃P₇ from liquid NH₃ yields the triammoniate Cs₃P₇·3 NH₃, which loses the weakly bound NH₃ of crystallization below 253 K. A low-temperature crystal-structure analysis shows that Cs₃P₇· NH₃ consists of a framework of heptaphosphanortricyclane anions P and Cs⁺ cations with NH₃ molecules completing the coordination of the cations. The framework is built from Cs₃P₇ layers connected by only few Cs…?P interactions, the interlayer gap being filled by a two-dimensional network of NH₃. The Cs₇P₇ part of the structure completes a family of alkali-metal-polyphosphide substructures which range from [RbP₇]^2? or [CsP₁₁]^2? chains over [Cs₂P_n]^? layers (n = 7, 11) to now [Cs₃P₇] frameworks.     

The lowest order relativistic corrections for the hydrogen molecule

We have calculated the lowest order relativistic corrections for the X ¹Σ, B¹Σ, a³Σ, b³Σ, I¹Π_g, C¹Π_u, i³Π_g, c³Π_u, J¹Δ_g, and j³Δ_g states of the hydrogen molecule using variational Monte Carlo methods and compact, explicitly correlated trial wavefunctions. Our values are in good agreement with earlier calculations on the X¹Σ and B¹Σ states. For the other states, our work provides the first estimate of these properties. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Proof of the Existence of a Linear,Centrosymmetric Polyiodide Ion I: the crystal structure of Cu(NH3)4 I4

Tetrammine-copper(II)-tetraiodide Cu(NH₃)₄I₄ crystallizes in the monoclinic space group C 2/m. The crystal structure has been determined from X-ray diffractometer data and refined to R_w = 2.2%. Four coplanar nitrogen atoms and two axial iodine atoms form an octahedral coordination around Cu(II) with a pronounced 4 + 2 tetragonal distortion. A connection of the Cu(II) atoms by linear, centrosymmetric I polyiodide ions results in infinite chains of [Cu(NH₃) I]-units. The central I-I-bond distance in I is 2.802(1) Å; a considerable amount of I-I bonding is indicated by the distance of 3.342(1) Å found for the terminal bonds. These intramolecular bond distances correspond to calculated I-I-bond orders of 0.80 and 0.43.     

Röntgenographische Untersuchungen und Strukturchemie von Chalkogenomolybdaten und -wolframaten

X-Ray Investigations and Structure Chemistry of Chalkogenomolybdates and - tungstates. I. Crystallographic data of compounds of the type A₂MeX₄, A₂MeOX₃, and A₂MeO₂X₂ (A = K, NH, Rb, Cs; (Me = Mo, W; X = S, Se) are discussed and general trends are illustrated. The molybdates and tungstates A₂MeX₄ and A₂MeOX₃ (A = K, NH, Rb, Cs; X = S, Se) crystallize in the rhombic space group D? Pnma. The compounds (NH₄)₂MeO₂X₂ (Me = Mo, W; X = S, Se) crystallize in the monoclinic space group C? C2/c.     

Hydrogen Generation by Visible Light Irradiation of Aqueous Solutions of Metal Complexes. An approach to the photochemical conversion and storage of solar energy

We describe a photochemical system for the generation of hydrogen by water reduction under visible light or sunlight irradiation of aqueous solutions containing the following components: a photosensitizer, the Ru (bipy) complex, for visible light absorption; a relay species, the Rh (bipy) complex, which mediates water reduction by intermediate storage of electrons via a reduced state; an electron donor, triethanolamine (TEOA) which provides the electrons for the reduction process and a redox catalyst, colloïdal platinum, which facilitates hydrogen formation. The conditions for efficient hydrogen production and the influence of the concentration of the components have been investigated; the metal complexes act as catalysts with high turnover numbers; excess bipyridine facilitates the reaction. The process contains two catalytic cycles: a ruthenium cycle and a rhodium cycle. The Ru cycle involves oxidative quenching of the *Ru(bipy) excited state by Rh(bipy) forming Ru(bipy) which is converted back to Ru(bipy) by oxidation of the electron donor TEOA, which is thus consumed. The Rh cycle comprises a complicated set of transformations of the initial Rh(bipy) complex. The reduced rhodium complex formed in the quenching process undergoes a series of transformations involving the Rh(bipy) complex and hydridorhodium-bipyridine species, from which hydrogen is generated by reaction with the protons of water. In view of the storage of two electrons in the reduced rhodium species, the process is formally a dielectronic water reduction. The properties and eventual participation of [Rh(III)(bipy)₂LL′]ⁿ⁺(L,L′ = H₂O, OH^?) species are investigated. It is concluded that at neutral pH in presence of excess bipyridine, the cycle involving regeneration of the Rh(bipy) complex is predominant. A number of experiments have been performed with modified systems. Hydrogen evolution is observed with other photosensitizers (like proflavin), other relay species (like Rh(dimethylbipy) or Co(II)-bipyridine complexes), other donor species, or in absence of the platinum catalyst. It also occurs in absence of photosensitizer by sunlight of UV. irradiation of Rh(bipy) or by visible light irradiation of iridium (III)-bibyridine complexes. These systems deserve further investigations. The present photochemical hydrogen generating system represents the reductive component of a complete water splitting process. Its role in solar energy conversion and in photochemical fuel production is discussed.     

Structure and dissociation energy of weakly bound H (n = 5−8) complexes

The geometrical parameters, vibrational frequencies, and dissociation energies for H (n = 5–8) clusters have been investigated using high level ab initio quantum mechanical techniques with large basis sets. The highest level of theory employed in this study is TZ2P CCSD(T). The C₁ structure of H is predicted to be a global minimum, while the C_s structure of H is calculated to be a transition state. Harmonic vibrational frequencies are also determined at the DZP and TZ2P CCSD levels of theory. The dissociation energies, D_e, for H (n = 5–8) have been predicted using energy differences at each optimized geometry, and zero‐point vibrational energies (ZPVEs) are considered to compare with experimental values. The dissociation energies (D_o) have been predicted to be 1.69, 1.65, 1.65, and 1.46 kcal · mol for H, H, H (C₁ symmetry) and H, respectively, at the TZ2P CCSD(T) level of theory. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Chemie der Seltenen Erden in geschmolzenen Alkalihalogeniden. XI. Spezifische elektrische Leitfähigkeiten und Aktivierungsenergien von Lanthaniden(III)-jodid–Alkalijodid-Schmelzen

Specific electrical conductivities and activation energies of the molten binary systems RJ₃–MeJ (R = La, Nd, Gd, Dy; Me = Na; K, Cs) have been investigated. In the mixtures with Me = K, Cs there are clear indications to species like RJ, RJ or R₂J.     

Gaussian wave functions for CH3 and NH

Ground state single determinant LCAO-MO-SCF wave functions, using a large contracted Gaussian basis set (6^s, 2^p, 1^d/3^s, 1^p), have been computed for the 9 electron molecular systems of CH₃ and NH. The minimum energies obtained using Roothaan's open shell SCF procedure for the planar equilibrium geometries were ?39.5703 Hartree for CH₃ and ?55.8945 Hartree for NH. Additional properties such as electron populations and multiple moments were calculated from the planar wave functions.