Jahn—Teller effects in substituted benzene cations. V. Quadratic coupling

A calculation model is derived for taking into account quadratic, in addition to linear, coupling Jahn—Teller effects in determining vibronic energy levels and transitions. Procedures are developed for analysis of Jahn—Teller electronic spectra on this basis and the new features, with respect to the linear coupling approximation, brought about by introduction of quadratic coupling, are discussed. Vibronic analyses of the B?² A″₂-X?²E″ transitions of 1,3,5-C₆F₃H⁺₃, 1,3,5-C₆F₃D⁺₃ and 1,3,5-C₆Cl₃H⁺₃ are carried out, in particular for bands involving excitation of the mode 6 vibration. Experimental evidence for quadratic Jahn—Teller effects is obtained for the sym-trifluorobenzene ions and the linear coupling parameters D₆, ω₆ and quadratic coupling parameter q₆ are derived. Two possible orders of magnitude of the quadratic coupling strength are found to be compatible with the spectra of 1,3,5-C₆Cl₃H⁺₃. The analyses are consistent between the three ions and are not in contradiction with the general findings based on the linear approximation alone.     

Vibrational-state-selected ion—molecule reaction cross sections at thermal energies

A method designed to measure relative ion—molecule reaction rates at thermal collision energies for selected reactant ion vibrational states is described. Relative reaction rates are determined for the three endothermic reactions: H₂⁺ (υ)(He,H)HeH⁺, H₂⁺ (υ)(Ne,H)NeH⁺, D₂⁺(υ)(Ne, D)NeD⁺, and for the two exothermic reactions H₂⁺ (υ)(H₂, H)H₃⁺, D₂⁺(υ)(D₂, D)D₃⁺, whereby data are evaluated for υ = 0–8 for H₂⁺ and for υ = 0–12 in the case of D₂⁺. The results are analyzed in terms of a modified statistical model designed for reactions that go through a collision complex. It is found that all data can be satisfactorily described within this model.     

Molecular fragmentations: Part II. Structures and energies of molecular fragments derived from formamide and its molecular cation

Molecular geometries and heats of formation have been calculated, using MINDO/3, for mass spectral fragment pairs (A⁺ + B) derived from formamide. There are five stable isomeric forms of the molecular ion: [H₂NC(OH)]⁺, (H₃NCO)⁺, [HNC(OH₂)]⁺, [NCH(OH₂)]⁺, and (NCOH₃)⁺ (in order of increasing

, but no isomer (H₂NCHO)⁺. There are three isomeric forms of (M—H)⁺: (H₂NCO)⁺ (HNCOH)⁺, and (NCOH₂)⁺: the only stable form of (M—2H)⁺ is (NCOH)⁺. Other (A/B)⁺ fragment pairs calculated are (CO/NH₃)⁺, (HCO/NH₂)⁺, (H₂O/HCN)⁺, (H₂O/HNC)⁺ [HO^. + (HCNH)⁺], and [HO^. + (H₂NC)⁺]. The structure of the doubly charged ion M²⁺ is also reported.     

Solid‐state architecture of saccharin salts of some diamines

Hydrazinium saccharinate, N₂H₅⁺·C₇H₄NO₃S⁻, crystallizes in a 1:1 ratio, while ethyl­ene­diaminium bis­(saccharinate), C₂H₁₀N₂²⁺·2C₇H₄NO₃S⁻, and butane‐1,4‐diaminium bis­(sac­charin­ate), C₄H₁₄N₂²⁺·2C₇H₄NO₃S⁻, form in a 1:2 cation–anion stoichiometry. The structures contain many strong hydrogen bonds of the N⁺—H⋯N⁻, N⁺—H⋯O, N—H⋯O and N—H⋯N types, with auxiliary C—H⋯O inter­actions.     

Molecular fragmentations: Part IX. Structures and energies of mass spectral fragments derived from xanthan hydride, 5-amino-1,2,4-dithiazolin-3-thione

Structures and energies have been calculated, in the MNDO approximation, for xanthan hydride (C₂H₂N₂S₃) and its molecular cation, and for the mass spectral fragment ions H₂NCNCS⁺, HNCNCS⁺, CS₂⁺, H₂N₂CS⁺ (two isomers), HN₂CS⁺, S₂⁺, H₂NCS⁺ (three isomers), HNCS⁺ (two isomers), H₃N₂C₂⁺ (four isomers), CS⁺ and HNCS⁺² (two isomers), together with the corresponding neutral fragments.     

Isomorphous crystals of strychninium 4‐chloro­benzoate and strychninium 4‐nitro­benzoate

In strychninium 4‐chloro­benzoate, C₂₁H₂₃N₂O₂⁺·C₇H₄ClO₂⁻, (I), and strychninium 4‐nitro­benzoate, C₂₁H₂₃N₂O₂⁺·C₇H₄NO₄⁻, (II), the strychninium cations form pillars stabilized by C—H⋯O and C—H⋯π hydrogen bonds. Channels between the pillars are occupied by anions linked to one another by C—H⋯π hydrogen bonds. The cations and anions are linked by ionic N—H⁺⋯O⁻ and C—H⋯X hydrogen bonds, where X = O, π and Cl in (I), and O and π in (II).     

Semi-empirical Scf-Mo study of the mass spectral fragmentation of tetramethyldiphosphine

Structures and enthalpies of formation have been calculated, in the MNDO approximation using UHF wave-functions for open shell species, for tetramethyldiphosphine, Me₄P₂, and the major ions in its mass spectrum: Me₄P₂⁺, Me₃P₂H⁺, Me₃P₂⁺, Me₂P₂H₂⁺ (3 forms), Me₂P₂H⁺ (3 forms), Me₂P₂⁺ (3 forms), MePPCH₂⁺ (3 forms), MeP₂⁺ and MePCH₂⁺, together with all the corresponding neutral fragments. Appearance potentials are calculated for all the ions, and possible fragmentation pathways deduced.     

On the sudden approximation of cross: computational tests and factorization of cross sections and related scattering phenomena

A sudden approximation recently derived by Cross using a semiclassical treatment of the orbital motion is recast into a form which permits factorization of differential and integral degeneracy averaged cross sections, opacities as a function of final angular momentum quantum number, the scattering amplitude, and the phenomenological cross section which describes spectral line broadening. Calculations are done using an average of initial and final orbital angular momentum quantum numbers for the partial wave parameter for ArN₂, ArTIF, H⁺H₂ and Li⁺H₂. The results indicate that the method is a good approximation for integral cross sections and opacities when the energy sudden approximation is valid and when the coupling of the orbital motion is important.     

Structure and properties of H2CN,H2CC−, H2BO and H2CO+

Ab initio SCF—MO calculations are presented for H₂CN, H₂CC^?, H₂BO and H₂CO⁺, including geometry optimization. One-electron properties are presented and compared with experiment where possible, particularly ESR hyperfine data.     

Photofragmentation of 2‐Deoxy‐D‐Ribose Molecules in the Gas Phase

We have measured the synchrotron‐induced photofragmentation of isolated 2‐deoxy‐D ‐ribose molecules (C₅H₁₀O₄) at four photon energies, namely, 23.0, 15.7, 14.6, and 13.8 eV. At all photon energies above the molecule′s ionization threshold we observe the formation of a large variety of molecular cation fragments, including CH₃⁺, OH⁺, H₃O⁺, C₂H₃⁺, C₂H₄⁺, CH_xO⁺ (x=1,2,3), C₂H_xO⁺ (x=1–5), C₃H_xO⁺ (x=3–5), C₂H₄O₂⁺, C₃H_xO₂⁺ (x=1,2,4–6), C₄H₅O₂⁺, C₄H_xO₃⁺ (x=6,7), C₅H₇O₃⁺, and C₅H₈O₃⁺. The formation of these fragments shows a strong propensity of the DNA sugar to dissociate upon absorption of vacuum ultraviolet photons. The yields of particular fragments at various excitation photon energies in the range between 10 and 28 eV are also measured and their appearance thresholds determined. At all photon energies, the most intense relative yield is recorded for the m/q=57 fragment (C₃H₅O⁺), whereas a general intensity decrease is observed for all other fragments— relative to the m/q=57 fragment—with decreasing excitation energy. Thus, bond cleavage depends on the photon energy deposited in the molecule. All fragments up to m/q=75 are observed at all photon energies above their respective threshold values. Most notably, several fragmentation products, for example, CH₃⁺, H₃O⁺, C₂H₄⁺, CH₃O⁺, and C₂H₅O⁺, involve significant bond rearrangements and nuclear motion during the dissociation time. Multibond fragmentation of the sugar moiety in the sugar–phosphate backbone of DNA results in complex strand lesions and, most likely, in subsequent reactions of the neutral or charged fragments with the surrounding DNA molecules.     

Photoelectron—photoion-coincidence measurements on 2,4-hexadiyne

2,4-Hexadiyne cations in their first excited electronic state òE_ureveal a decay by an effective competition between fluorescence and fragmentation. The present photoelectron—photoion-coincidence study of 2,4-hexadiyne cation provides individual breakdown diagrams for the parent ion and the seven dominant fragment ions, C₆H₅⁺, C₆H₄⁺, C₅H₃⁺, C₄H₄⁺, C₄ H₃⁺, C₄H₂⁺, C₃H₃⁺ in the ionisation energy regions populated by He(Iα) excitation. Additional information concerning the rate constants and the kinetic energy released on the formation of C₆H₅⁺ and C₄H₃⁺ are deduced from the time-of-flight (TOF) distributions of these ions. The appearance potentials for the two fragments C₄H₃⁺ and C₄H₂⁺ could also be measured, as these lie well within the third band of the He(Iα)-PE spectrum.     

Electronic structures and configurational transformations of some protonated compounds

The equilibrium geometries of HCHOH⁺, CH₃CHOH⁺, (CH₃)₂COH⁺, HCO₂H⁺₂, and CH₃CO₂H⁺₂ were determined by means of the semiempirical INDO—SCF method. The total-energy difference between the protonated isomers was found to be reasonable as compared with that obtained from the NMR observations. The computed barriers of the transformation between the isomers via the pure or distorted rotation or the bending motion were in good agreement with the experimental results.     

Three‐dimensional networks in bis(imidazolium) 2,2′‐dithiodibenzoate and 4‐methylimidazolium 2‐[(2‐carboxyphenyl)disulfanyl]benzoate

Cocrystallization of imidazole or 4‐methylimidazole with 2,2′‐dithiodibenzoic acid from methanol solution yields the title 2:1 and 1:1 organic salts, 2C₃H₅N₂⁺·C₁₄H₁₀O₄S₂²⁻, (I), and C₄H₇N₂⁺·C₁₄H₁₀O₄S₂⁻, (II), respectively. Compound (I) crystallizes in the monoclinic C2/c space group with the mid‐point of the S—S bond lying on a twofold axis. The component ions in (I) are linked by intermolecular N—H...O hydrogen bonds to form a two‐dimensional network, which is further linked by C—H...O hydrogen bonds into a three‐dimensional network. In contrast, by means of N—H...O, N—H...S and O—H...O hydrogen bonds, the component ions in (II) are linked into a tape and adjacent tapes are further linked by π–π, C—H...O and C—H...π interactions, resulting in a three‐dimensional network.     

Eclipsed and staggered conformations of (SIH3)2F+: An ab initio study

Ab initio calculations at 6–31G**, 6–31++G**, and MP2/6–31G** levels were performed on disilyl–fluoronium, (SiH₃)₂F⁺, with the SiH₃ group eclipsed or staggered. Optimized geometries, total energies, dipole moments, atomic charges, electronic density, and vibrational frequencies were computed. The results were compared with calculated structural parameters and vibrational frequencies of H₃SiF, H₂SiF⁺, H₂SiF^?, and H₄SiF⁺ ions. The basis-set effects were studied. Several thermochemistry parameters—ZPE, thermal energy, rotational constants, and entropies—were also calculated. © 1994 John Wiley & Sons, Inc.     

The proton‐coupled proton transfer mechanism,H2O catalysis,and hydrogen tunneling effects in the reaction of HNCH2 with HCOOH in the interstellar medium

The reaction HNCH₂ + HCOOH → H₂NCH₂COOH is supposed to be an important reaction related to the possible origin of amino acids on the early Earth. We find that it has an energy barrier of 87.37 kcal mol⁻¹ obtained with MP2/6‐311+G** in the gas phase, but it is likely enhanced to occur in the interstellar medium (ISM) through a proton‐coupled proton transfer reaction, initiated by HNCH₂ coupled with H₂⁺, H₃⁺, or H₃⁺O. H₂⁺, H₃⁺, and H₃⁺O serve as a donor of energy in the coupled reactions. H⁺, which is a key species to the coupled reactions, further, plays a catalytic role in reducing a barrier up to 14.14 kcal mol⁻¹. In the coupled reaction with H₃⁺O, H₂O, which can seize, transport, and deliver a proton from HCOOH to H₂NCH₂⁺, reduces a barrier up to 14.96 kcal mol⁻¹. A significant hydrogen‐tunneling pathway is predicted by the temperature dependences of k_H^CVT/SCT, calculated using the small curvature tunneling (SCT) approximation and canonical variational transition state theory (CVT). Hydrogen tunneling is another important mechanism to make the reaction happen in the ISM. The achieved results can be applied to discuss the origin of amino acids from the materials of the Earth itself. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Three‐dimensional networks in 5‐methylimidazolium 3‐carboxy‐4‐hydroxybenzenesulfonate and bis(5‐methylimidazolium) 3‐carboxylato‐4‐hydroxybenzenesulfonate

The two title proton‐transfer compounds, 5‐methylimidazolium 3‐carboxy‐4‐hydroxybenzenesulfonate, C₄H₇N₂⁺·C₇H₅O₆S⁻, (I), and bis(5‐methylimidazolium) 3‐carboxylato‐4‐hydroxybenzenesulfonate, 2C₄H₇N₂⁺·C₇H₅O₆S²⁻, (II), are each organized into a three‐dimensional network by a combination of X—H...O (X = O, N or C) hydrogen bonds, and π–π and C—H...π interactions.     

catena‐Poly­[[di­aqua­lithium(I)]‐μ‐[9H‐purine‐2,6(1H,3H)‐dionato‐O2:N7]]

In the title compound, [Li(C₅H₃N₄O₂)(H₂O)₂]_n, the coordinate geometry about the Li⁺ ion is distorted tetrahedral and the Li⁺ ion is bonded to N and O atoms of adjacent ligand mol­ecules forming an infinite polymeric chain with Li—O and Li—N bond lengths of 1.901 (5) and 2.043 (6) Å, respectively. Tetrahedral coordination at the Li⁺ ion is completed by two cis water mol­ecules [Li—O 1.985 (6) and 1.946 (6) Å]. The crystal structure is stabilized both by the polymeric structure and by a hydrogen‐bond network involving N—H?O, O—H?O and O—H?N hydrogen bonds.     

N—H...S and C—H...S hydrogen bonds in two tetraalkylammonium dithiobiurea(1–) inclusion compounds

Two inclusion compounds of dithiobiurea and tetrapropylammonium and tetrabutylammonium are characterized and reported, namely tetrapropylammonium carbamothioyl(carbamothioylamino)azanide, C₁₂H₂₈N⁺·C₂H₅N₄S₂⁻, (1), and tetrabutylammonium carbamothioyl(carbamothioylamino)azanide, C₁₆H₃₆N⁺·C₂H₅N₄S₂⁻, (2). The results show that in (1), the dithiobiurea anion forms a dimer via N—H...N hydrogen bonds and the dimers are connected into wide hydrogen‐bonded ribbons. The guest tetrapropylammonium cation changes its character to become the host molecule, generating pseudo‐channels containing the aforementioned ribbons by C—H...S contacts, yielding the three‐dimensional network structure. In comparison, in (2), the dithiobiurea anions are linked via N—H...S interactions, producing one‐dimensional chains which pack to generate two‐dimensional hydrogen‐bonded layers. These layers accommodate the guest tetrabutylammonium cations, resulting in a sandwich‐like layer structure with host–guest C—H...S contacts.     

From [M≡N] and [M—N—E] Complexes to Models for Metal Oxidoreductases

The article reviews results of research that was initially aiming at complexes containing new and unusual [M—N—E] element combinations (M = transition metal, E = main group element), but soon turned into studies on model complexes for metal enzymes such as nitrogenases, hydrogenases or CO dehydrogenases, because several of the resulting [M—N—E] complexes exhibited reactions relevant to these enzymes. It could be shown that alkylation of transition metal thiolate nitride complexes gives alkylimido complexes when bulky and mild alkylation reagents, e.g. Ph₃C⁺, are used. Hydride addition to [Ru(NO)(py^buS₄)]⁺ yielded [Ru(HNO)(py^buS₄)], which contains a bifurcated [M—N(X, Y)] bridge. The diazene complex [μ‐N₂H₂{Ru(PCy₃)(S₄)}₂] undergoes H⁺/D⁺ and H⁺/D₂ exchange reactions that enabled to rationalize the until then inexplicable ‘N₂ dependent HD formation’ catalyzed by nitrogenases. Out of a larger number of [Ni(NE)(S₃)] complexes, the compound [Ni(NHPPr₃)(S₃)] proved capable to model structure and reactivity features of [NiFe] hydrogenases. The [Ni(L)(S₃)] complexes with L = N₃^— and N(SiMe₃)₂^— exhibit extremely high reactivity towards CO, CO₂ and SO₂. The reactions lead to NCO^—, CN^— and NSO^— complexes and bear potential relevance for carbon monoxide dehydrogenase reactions.     

Polysulfonylamine. CLXIII [1] Kristallstrukturen von Metall‐di(methansulfonyl)amiden. 12 [1] Das orthorhombische Doppelsalz Na2Cs2[(CH3SO2)2N]4·3H2O: Ein dreidimensionales Koordinationspolymer aus (Caesium‐Anion‐Wasser)‐Schichten und intercalierten Natriumionen

Polysulfonylamines. CLXIII. Crystal Structures of Metal Di(methanesulfonyl)amides. 12. The Orthorhombic Double Salt Na₂Cs₂[(CH₃SO₂)₂N]₄·3H₂O: A Three‐Dimensional Coordination Polymer Built up from Cesium‐Anion‐Water Layers and Intercalated Sodium Ions The packing arrangement of the three‐dimensional coordination polymer Na₂Cs₂[(MeSO₂)₂N]₄·3H₂O (orthorhombic, space group Pna2₁, Z′ = 1) is in some respects similar to that of the previously reported sodium‐potassium double salt Na₂K₂[(MeSO₂)₂N]₄·4H₂O (tetragonal, P4₃2₁2, Z′ = 1/2). In the present structure, four multidentately coordinating independent anions, three independent aquo ligands and two types of cesium cation form monolayer substructures that are associated in pairs to form double layers via a Cs(1)—H₂O—Cs(2) motif, thus conferring upon each Cs⁺ an irregular O₈N₂ environment drawn from two N, O‐chelating anions, two O, O‐chelating anions and two water molecules. Half of the sodium ions occupy pseudo‐inversion centres situated between the double layers and have an octahedral O₆ coordination built up from four anions and two water molecules, whereas the remaining Na⁺ are intercalated within the double layers in a square‐pyramidal and pseudo‐C₂ symmetric O₅ environment provided by four anions and the water molecule of the Cs—H₂O—Cs motif. The net effect is that each of the four independent anions forms bonds to two Cs⁺ and two Na⁺, two independent water molecules are involved in Cs—H₂O—Na motifs, and the third water molecule acts as a μ₃‐bridging ligand for two Cs⁺ and one Na⁺. The crystal cohesion is reinforced by a three‐dimensional network of conventional O—H···O=S and weak C—H···O=S/N hydrogen bonds.