The triethylammonium-pyridine complex cation

The infrared spectra of the hydrogen bonded complex cation (triethylamine H⁺ pyridine) and of the three similar cations resulting from deuterium substitution in pyridine and at the bridge, have been examined in solution. The bridging proton occupies a potential with a single minimum closer to the triethylamine moiety. The V_s band structure is ascribed to Fermi resonance with triethylamine mode combinations. The N · N stretching mode of this complex, and also of the (trimethylamine H⁺ pyridine) complex have been observed in the far-infrared range.The present complex is weaker than the corresponding trimethylamine one.     

Complex hydrogen bonded cations-V further asymmetric ions

Solutions have been prepared containing the complex cations (¹BH²B)⁺, where the differing bases may be pyridine, 4-Me pyridine, NMe imidazole, thiazole, isooxazole, trimethylamine or NMe piperidine. The infrared spectra usually show a double maximum in the v_s band, the intensity of the lower component decreasing as the difference in the pKa's of the bases increases. In the D-bridged analogues only a single v_sband occurs. Other features of the spectra indicate that the bridging proton potential is asymmetric. The lower frequency component of the v_s band of the H-bonded system is attributed to Fermi resonance, not proton tunnelling. The proton potential in these and the related symmetric complex cations is reviewed.     

Synthesis and structure of pseudotetrahedral Co(II) zwitterionic complexes: trichloro(1-methylpiperazin-1-ium-N4)cobalt(II) and trichloro(1,4-dimethylpiperazin-1-ium-N4)cobalt(II)

The pseudotetrahedral cobalt(II) zwitterionic complexes, [CoCl₃(H₂Meppz)] (1) [H₂Meppz⁺=1-methylpiperazin-1-ium cation] and [CoCl₃(HMe₂ppz)] (2), [HMe₂ppz⁺=1,4-dimethylpiperazin-1-ium cation] have been synthesized and characterized in the solid state by X-ray single crystal analysis, IR spectra, magnetic measurements and electronic spectra. In both the compounds the cobalt(II) center is coordinated in a distorted tetrahedral fashion by the three chloride ions and by one nitrogen of the piperazine ring that retains the more stable chair conformation. The distorted coordination polyhedron in complex 1 preserves the C_3v symmetry while in complex 2 it retains only the m symmetry. In complex 1, the (H₂Meppz)⁺ cation binds the Co(II) ion in the equatorial position of the piperazine ring using the unmethylated N1–H nitrogen atom that is less hindered than the methylated one. Complex 2, on the contrary, is a novelty being the first example of a Co(II) ion bound in the axial position of a piperazine ring, this produces a long Co(II)–N bond, 2.108(4) Å. Electronic spectra in the solid state are in perfect accordance with the X-ray crystallographic results indicating a C_3v symmetry for complex 1 and a C_s(m) symmetry for complex 2. These complexes present strong two-center and three-center hydrogen bonds of N⁺–H⋯Cl type.     

Acidité dans le nitrométhane: III. Détermination électrochimique de la basicité du nitrométhane — Corrélation Dn/Eo(Hs+/H2/

The use of the complex acid HAlCl₄ (HCl+AlCl₃) permits the detemrination of the standard potential of the hydrogen electrode in nitromethane. The result (E₀(H_s⁺/H₂)=0.5 V vs. Fc/Fc⁺, Fc=ferrocene) shows that nitromethane is very weakly basic. This measurement is confirmed by showing that the standard potential of the hydrogen electrode in various solvents is linked to Gutmann's donor numbers of these solvents. The E₀(H_s⁺/H₂) value obtained in nitromethane belongs to the correlation line.     

Infrared spectra of the ammonium ion in ammonium metavanadate NH4VO3

The ND stretching modes of isotopically dilute NH₃D⁺ ions in NH₄VO₃ are in agreement with the predicted splitting into C_s, C_s and C₁(2) components under C_s site symmetry for the NH⁺₄ ion. The three bands observed represent the three NH bonding distances in the crystal, and the position, shape and low temperature behaviour of each band confirms the existence of two types of hydrogen bonding in NH₄VO₃. The low temperature infrared modes of NH⁺₄ and ND⁺₄ in NH₄VO₃ and ND₄VO₃, respectively, can be assigned under space group Pbcm. Temperature dependence of these modes also reflects the presence of both normal and bifurcated hydrogen bonds in NH₄VO₃.     

Complex hydrogen bonded cations: III. Asymmetric ions

Spectroscopic evidence is presented for the occurrence of a number of asymmetric complex cations, of formula (B¹B²)⁺ where B¹ and B² differ, and may be pyridine, 4-methylpyridine, 2,6- and 3,5-dimethylpyridine, 2,4,6-trimethyl-pyridine, 2-fluoropyridine, 3-chloropyridine or quinoline. In the H-bridged cations, the NH stretching band v_s is doubled, the ratio of the intensities of the components varying regularly with AΔpK_a of the component bases. In the D-bridged cations, only a single v_s band is observed. All features in the spectra evolve continuously from those of the symmetric cations (B¹ = B²).     

Structural roles of water in potassium nitrilosulphonate dihydrate,K3N(SO3)3.2H2O

The structural roles of the two types of lattice water in K₃N(SO₃)₃.2H₂O have been determined from the geometries of their immediate environments. Through hydrogen bonds of different lengths (and hence strengths), H₂O(1) links adjacent N(SO₃)₃^3?ions belonging to the same unit cell and lying on the same crystallographic mirror plane as O(1).H₂O(2) links identical N(SO₃)₃^3?ions contained in unit cells adjacent in the b direction, by very weak, equivalent hydrogen bonds. The hydrogen atoms of H₂O(1) are assigned to C_s sites in the unit cell and those of H₂O(2) are assigned to C₁ sites. The proposed site occupancies are verified by infrared spectroscopy using the “isotopic dilution” technique.     

The line profiles of single rotational lines of the H 2 B - X(3, 0) band in an intense infrared light field

The first investigation of the lineshape of single rotational lines of the H ₂ B - X(3, 0) band in an intense infrared light field (λ = 1064 nm) at intensities between 10¹⁰ W/cm² and 10¹² W/cm² is reported. The B - X(3, 0) band is excited with low intensity vacuum ultraviolet radiation (λ ≈ 106 nm). B-state excitation is observed by multiphoton ionization and dissociation of H ₂ with H ⁺ as final product. The lineshapes of the B-X(3, 0) band behave differently in both decay channels. This indicates that they branch before the molecule is photoionized. The intensity dependence of the lineshapes seems to show that at certain intensities in the focused infrared light beam the AC-Stark effect induces transient resonances into the multiphoton excitation process starting at the B(v = 3, J) rotational levels. A qualitative analysis of the states which may influence the B(v = 3, J) multiphoton excitation rate is given.     

The far infrared spectra of metal chloride complexes of pyridine in relation to their structures

The infrared spectra of the complexes [M(py)₂Cl₂] (py = pyridine; M = Mn, Fe, Co, Ni, Cu, Zn) have been determined within the range 650–150 cm^?1. Assignments of the metal—nitrogen and metal—halogen stretching frequencies (vM—N and vM—Cl) are made on the basis of the band shifts induced by deuteration of the pyridine ring and by varying the coordinated metal ion. If the band of lowest frequency is assigned to a bending mode, the number of vM—N and vM—Cl bands observed agrees with the number required by symmetry considerations based on the known structures of the complexes. On the basis of this work, some earlier assignments have been revised.     

Infrared and paH correlation of proton transfer in and bridges in acetonitrile

Hydrogen bond complexing (BHB)⁺ between N-bases and their cations has been examined by infrared spectroscopy and potentiometry. In the acetonitrile (AN) solution there have been studied hetero-systems (B + B₁H⁺), where the differing bases, B, may be triethylamine, N-methylpiperidine, morpholine, N-methylimidazole, pyridine, 2- and 3-chloropyridine, quinoline and trimethyl-N-oxide with B₁H⁺ : trimethyl-N-oxideH⁺ and N-methylimidazoleH⁺. Homocomplex (Me₃NO)₂H⁺ has been distinguished. In the H-bridges cation the stretching band ν_s (NH⁺) and (−OH⁺) are dependent directly on the p_aH and formation constant K_f of the component bases.     

Polarisation effects in electron transfer reactions with laser excited Na(3P) at medium energies

We report new experimental data for the investigation of the role of electronic orbital alignment and orientation in charge transfer processes, in the medium energy range where the collision velocityv _c and the velocity of the active electronv _e are of the same order of magnitude. The results obtained for the H ₂ ⁺ -Na(3p) and He⁺-Na(3p) collisions are discussed in comparison with the experimental and theoretical findings obtained for the H⁺-Na(3p) system. Recent time-of-flight measurements for charge transfer in Li⁺-Na(3s and 3p) collisions are also presented.     

Reactions of HBr+ ions in the 2Π i , v + quantum states with H2 and HBr molecules

The mechanisms and kinetics of low-temperature ion-molecular reactions between the Br⁺, HBr⁺, and DBr⁺ions and the HBr, DBr, H₂, and D₂ molecules were studied. The HBr⁺ (i,v ⁺) and DBr⁺(i,v ⁺) ions were prepared in separate spin-orbit (i) and vibrational (v ⁺) states by resonance multiphoton ionization in a free flow of halogen halides (HBr and/or DBr) with hydrogen, deuterium, or inert gases (Ar, He). The effectiveness of various reaction channels, including the exchange of charges, H and D atoms, and H⁺andD⁺ ions, was studied. The quantitative data on the kinetics of these reactions were obtained for separate quantum states of the ions. The resonance ionization of one of the two ion isotopomers H⁷⁹Br⁺(D⁷⁹Br⁺) or H⁸¹Br⁺(D⁸¹Br⁺) was used to study and compare the effectiveness of various ion-molecular reaction channels.     

The structure of the NH2 group and its basicity

The fundamental symmetric (v^s) and antisymmetric (v^as) NH₂ stretching frequencies of some amine-containing compounds (aliphatic and aromatic amines, benzyl amines, and amides) have been measured in dilute CCl₄ solutions. The s-character of the hybrid orbitals of the N-H bonds (b²) has been calculated from v^s and v^as. The basicities (pK_BH⁺) of a number of compounds have been determined. The relationship between pK_BH⁺ and the amount of s-character of the N-H, bonds of the amino groups of the corresponding compounds has been obtained. Separate linear relationships have been found between the indicated values for each group of compounds. For anilines, which have the most highly electron-accepting substituents, there are deviations from the linear dependence b² = f(pK_BH⁺). Differences in the correlation character b² = f(pK_BH⁺) have been explained by a combination of the variations of the N-atom hybrid state and the population of the orbital's lone pair under the influence of substituents.     

Steric conditions and polarizability of structurally symmetrical interamoleculer hydrogen bonds in R-DI(α-pyridyl) hydroperchlorates

Seven R-di-(α-pyridyl) hydroperchlorates (R = (1) CH₂, (2) NH, (3) CO, (4) (CH₂)₂, (5) (CH₂)₃, (6) (CH₂)₄ and (7) S-S) were prepared and studied in acetonitrile-d₃ solutions by NMR and IR spectroscopy. With the hydroperchlorates of compounds 1 and 4, an equilibrium between non-hydrogen-bonded NH⁺ groups and intramolecular-bonded NH⁺ groups is present. With compounds 2, 3 and 5–7, the intramolecular hydrogen bonds are formed quantitatively. In compounds 4–7, the potential wells in these intramolecular structurally symmetrical N⁺H· N ? N · H⁺N bonds, are double minima. These hydrogen bonds are easily polarizable. With compounds 1–3, the distance between the N atoms given by the steric conditions of the molecules is smaller than with usual linear hydrogen bonds. Therefore, strong bent intramolecular structurally symmetrical hydrogen bonds are found, with relatively narrow single-minimum potential wells. These bonds cause a band in the region 3000–2500 cm^?1 instead of the continuum. Thus they are not easily polarizable.     

Nascent Rotational Distributions of MgH in Reaction of Mg(4s 1S0) with H2 and HD

The nascent rotational distributions of MgH(X²σ⁺, v″ = 0, 1) resulting from the reaction of Mg(4s¹S₀) with H₂ and HD have been determined by using the laser pump-probe technique. Like the case of Mg(¹P₁), the distributions appear to be bimodal which peak mainly at high N(26) with minor peaks at low N(6). There are no apparent differences when the escaping mass is doubled. The similarity between product rotational distributions from the 4S state and those from the 3P state, and no evidence of a kinematic isotope effect, reveal that a harpoon-type mechanism may be operative. Our ab initio calculations reveal that in the entrance channel on the 3¹A₁ surface in C_2v symmetry or ¹σ⁺ surface in C_∞v symmetry for 4S state, the reaction may lake place via a series of non-adiabatic curve crossings with the ionic Mg⁺H₂^? potential surface.     

Coordination behaviour of the multidentate Schiff base 2,6-bis(2-hydroxyphenyliminomethyl)pyridine towards the fac-[Re(CO)3] and [ReO] cores

The seven-coordinate rhenium(III) complex cation [Re^III(dhp)(PPh₃)₂]⁺ was isolated as the iodide salt from the reaction of cis-[Re^vO₂I(PPh₃)₂] with 2,6-bis(2-hydroxyphenyliminomethyl)pyridine (H₂dhp) in ethanol. In the complex fac-[Re(CO)₃(H₂dhp)Br], prepared from [Re(CO)₅Br] and H₂dhp in toluene, the H₂dhp ligand acts as a neutral bidentate N,N-donor chelate. The complexes were characterized by elemental analysis, infrared and ¹H NMR spectroscopy and X-ray crystallography.     

A surface hopping quasiclassical trajectory study of the H2+ + H2 and (H2 + D2)+ systems

In this work we use a complete surface hopping quasiclassical trajectory method to determine cross sections for the reactions H₂⁺ + H₂ → H₃⁺ + H and the isotopic variants (H₂⁺ + D₂ and D₂⁺ + H₂). Initial translational energies ranged between 0.5 and 6 eV. The vibrational quantum number (v⁺) of the charged diatom is either 0 or 3. Comparing these results with our previous results with a partial treatment of surface hopping, we find essentially no change for v⁺ = 0 and reductions in cross sections of up to 30% for v⁺ = 3 trajectories.     

Tabulation of infrared spectral data : David Dolphin and Alexander E. Wick,John Wiley,New York,London, Sydney and Toronto, 1977, pp. xvi + 549, price £14.65

The infrared spectra of the isotopically isolated NH₃D⁺ and HDO species have been examined in seven ammonium Tutton salts. The observed spectra are in good agreement with predictions based on the known crystallographic features of these salts. Linear regression of the ND stretching frequencies v₁(NH₃D⁺) of the isotopically isolated NH₃D⁺ ion on hydrogen-bonded distance d(N ? O) indicated the existence of a correlation ; subsequent fitting of the data to a more plausible empirical function v₁(NH₃D⁺) = v_1,∞,-k₁ exp(-k₂,d) resulted in a coefficient of determination of 0.94 and a standard deviation of 10 cm^?1 for the goodness of fit. The structural differences caused by the distortion of the metal coordination octahedron in the copper(II) Tutton salts are discussed. For this purpose the spectra of isotopically dilute HDO in the salts M₂ⁱ[Cu(H₂O)₆](SO₄)₂ (Mⁱ = K, Rb, Cs) have also been measured. No evidence of phase transformations between room and liquid-nitrogen temperatures was detected in the spectra of any of the saltri studied in this work.     

State-selected ion-molecule reactions: H+2(ν) + He → HeH+ + H and He + H+ + H

Total cross sections for production of HeH⁺ and H⁺ in the reaction of state-selected H⁺₂ (v = 0 to 6) with He at 3.1 eV c.m. collision energy are measured by means of the threshold-photoelectron/photoion coincidence method, using pulsed synchrotron radiation. Both reaction cross sections are observed to rise with vibrational energy. The H⁺/HeH⁺ branching ratio, which is determined directly, remains approximately constant at about 0.3 for v ⩽ 3 and rises gradually for higher levels to reach the value 1.3 for v = 6. For v ⩽ 3 both reactions involve hard-type collisions and result in large-angle scattering. In contrast, at higher v levels, the HeH⁺ becomes essentially forward scattered with respect to the incident He direction, but with a velocity greater than that expected from the spectator stripping model. The H⁺ products are backward scattered with respect to the incident H⁺₂ for v ⩽ 1 and receed faster from the He atom than the H products. This observation directly leads to the conclusion that collision-induced dissociation from v = 0 and 1 involves transitions to the first excited potential-energy surface.