Accurate DMBE Potential Energy Surface For the N(2D) + H2(1Σ g + ) Reaction Using an Improved Switching Function Formalism

A single-sheeted double many-body expansion (DMBE) potential energy surface is reported for the 1 ² A′′ state of NH₂. To approximate its true multi-sheeted nature, a novel switching function that imposes the correct behavior at the H₂(X ¹Σ _g ⁺)+ N(² D) and NH(X ³Σ^-) + H(² S) dissociation limits has been suggested. The new DMBE form is shown to fit with high accuracy an extensive set of new ab initio points (calculated at the multi-reference configuration interaction level using the full valence complete active space as reference and aug-cc-pVQZ and aug-cc-pV5Z basis sets) that have been semiempirically corrected at the valence regions by scaling the n-body dynamical correlation terms such as to account for the finite basis set size and truncated configuration interaction expansion. A detailed study of the N(² D) ... H₂(X ¹Σ _g ⁺) van der Waals region has also been carried out. These calculations predict a nearly free rigid-rotor with two shallow van der Waals wells of C _2v and C _{∞ v} symmetries. Such a result contrasts with previous cc-pVTZ calculations which predict a single T-shaped van der Waals structure. Except in the vicinity of the crossing seam, which is replaced by an avoided intersection, the fit shows the correct physical behavior over the entire configurational space. The topographical features of the new DMBE potential energy surface are examined in detail and compared with those of other potential functions available in the literature. Amongst such features, we highlight the barrier for linearization (11,802 cm^-1) which is found to overestimate the most recent empirical spectroscopic estimate by only 28 cm^-1. Additionally, the T-shaped N(² D) ... H₂ van der Waals minimum is predicted to have a well depth of 90 cm^-1, being 11 cm^-1 deeper than the C _{∞ v} minimum. The title DMBE form is therefore recommendable for dynamics studies of both non-reactive and reactive N(² D)+H₂ collisions.     

The molecular and crystal structure of bipolar,mesogenic biphenyls: a comparison of similar compounds HO(CH 2) 6 OC 6 H 4 C 6 H 4 R with R = cyano and nitro terminal groups

The crystal and molecular structures of 4,4′-disubstituted biphenyls of formula HO(CH₂)₆ OC₆H₄C₆H₄ R with R = cyano and nitro terminal groups have been determined including co-crystallized materials of both of the compounds. The extended molecules arrange in an antiparallel fashion with dipole-dipole interactions, exhibiting a sheet-like structure for the compound with the cyano terminal group, and for the other two materials an extended head to tail string-like structure caused by dipolar interaction, also packed in sheets in an antiparallel fashion by van der Waals interactions. Knowledge of the interaction of the compounds in the crystalline state serves as a prerequisite for the determination of interactions in the liquid crystalline state of the same or similar compounds.     

Calculations on the vertical and adiabatic ionization energies of (H2S)2

After determining reliable procedures for calculating the ionization energy of H₂S using many-body perturbation theory and electron propagator theory, the same procedures are used to calculate the vertical ionization energy of the van der Waals molecule (H₂S)₂. The adiabatic ionization energy calculated for a dimer cation with a H₃S⁺...SH structure is in satisfactory agreement with photoionization threshold experiments. An alternative dimer cation structure with a three-electron S-S bond is also discussed.     

Halogen–C2H2 Binding in Ultramicroporous Metal–Organic Frameworks (MOFs) for Benchmark C2H2/CO2 Separation Selectivity

Acetylene (C₂H₂) capture is a step in a number of industrial processes, but it comes with a high-energy footprint. Although physisorbents have the potential to reduce this energy footprint, they are handicapped by generally poor selectivity versus other relevant gases, such as CO₂ and C₂H₄. In the case of CO₂, the respective physicochemical properties are so similar that traditional physisorbents, such as zeolites, silica, and activated carbons cannot differentiate well between CO₂ and C₂H₂. Herein, we report that a family of three isostructural, ultramicroporous (<7 Å) diamondoid metal–organic frameworks, [Cu(TMBP)X] (TMBP=3,3′,5,5′-tetramethyl-4,4′-bipyrazole), TCuX (X=Cl, Br, I), offer new benchmark C₂H₂/CO₂ separation selectivity at ambient temperature and pressure. We attribute this performance to a new type of strong binding site for C₂H₂. Specifically, halogen ⋅⋅⋅ HC interactions coupled with other noncovalent in a tight binding site is C₂H₂ specific versus CO₂. The binding site is distinct from those found in previous benchmark sorbents, which are based on open metal sites or electrostatic interactions enabled by inorganic fluoro or oxo anions.     

Thermal electron attachment processes in gas mixtures containing H2S,HCl and HBr

The kinetics of thermal electron capture reactions by H₂S, HCl and HBr in mixtures with CO₂ have been investigated using the electron swarm method. A mechanism involving van der Waals molecules (H₂S)₂, (HCl·CO₂) and (HBr·CO₂) has been proposed and the rate constants have been calculated. Some tentative conclusions have been made concerning the influence of electronegativity and the dipole moment of the electron scavenger on the mechanism of the electron capture process.     

Syntheses of(C_8H_8)Ln(C_9H_7)·(THF)_2(Ln=Pr,Nd)and crystal structure of(C_8H_8)Pr(C_9H_7)·(THF)_2

This paper reports two lanthanide complexes of formula (C_9H_7)Ln(C_8H_8)·(THF)_2 whereLn is Pr or Nd,C_9H_7 is indenyl,and C_8H_8 is cyclooctatetraene (COT).The complexes were preparedby the reaction of LnCl_3 with K(C_9H_7) and K_2(C_8H_8) in THF.(C_9H_7)Pr(C_8H_8)·(THF)_2 crystallizes inTHF at - 15℃ in the monoclinic space group P2_1:with unit cell dimensions a=8.446(0),b=10.083(2),c=13.407(3),β=105.48(1)°,V=1100.43(35)~3,Dc=1.52g/cm~3 and Z=2.The final R valueis 0.033,R_w value is 0.030,respectively.In (C_9H_7)Pr(C_8H_8)·(THF)_2 a five-membered ring centroid ofC_9H_7,the C_8H_8 ring centroid and the two oxygen atoms from the two THF molecules form a distortedtetrahedral geometry around the metal.     

Synthesis,characterization and in vitro antitumor activity of some arylantimony ferrocenecarboxylates and crystal structures of C5H5FeC5H4CO2SbPh4 and (C5H5FeC5H4CO2)2Sb(4‐CH3C6H4)3

A series of arylantimony ferrocenecarboxylates with the formula (C₅H₅FeC₅H₄CO₂)_nSbAr_(5?n) (n = 1, 2; Ar = C₆H₅, 4‐CH₃C₆H₄, 3‐CH₃C₆H₄, 2‐CH₃C₆H₄, 4‐ClC₆H₄, 4‐FC₆H₄) were synthesized and characterized by elemental analysis, IR, ¹H NMR and mass spectra. The crystal structures of (C₅H₅FeC₅H₄CO₂)₂Sb(4‐CH₃C₆H₄)₃ and C₅H₅FeC₅H₄CO₂SbPh₄ were determined by X‐ray diffraction. Four human neoplastic cell lines (HL‐60, Bel‐7402, KB and Hela) were used to screen these compounds. The results indicate that these compounds at 10 µM show certain in vitro antitumor activities. Copyright © 2003 John Wiley & Sons, Ltd.     

Reactivity of the Indenyl Radical (C9H7) with Acetylene (C2H2) and Vinylacetylene (C4H4)

The reactions of the indenyl radicals with acetylene (C₂H₂) and vinylacetylene (C₄H₄) is studied in a hot chemical reactor coupled to synchrotron based vacuum ultraviolet ionization mass spectrometry. These experimental results are combined with theory to reveal that the resonantly stabilized and thermodynamically most stable 1-indenyl radical (C₉H₇^.) is always formed in the pyrolysis of 1-, 2-, 6-, and 7-bromoindenes at 1500 K. The 1-indenyl radical reacts with acetylene yielding 1-ethynylindene plus atomic hydrogen, rather than adding a second acetylene molecule and leading to ring closure and formation of fluorene as observed in other reaction mechanisms such as the hydrogen abstraction acetylene addition or hydrogen abstraction vinylacetylene addition pathways. While this reaction mechanism is analogous to the bimolecular reaction between the phenyl radical (C₆H₅^.) and acetylene forming phenylacetylene (C₆H₅CCH), the 1-indenyl+acetylene→1-ethynylindene+hydrogen reaction is highly endoergic (114 kJ mol⁻¹) and slow, contrary to the exoergic (−38 kJ mol⁻¹) and faster phenyl+acetylene→phenylacetylene+hydrogen reaction. In a similar manner, no ring closure leading to fluorene formation was observed in the reaction of 1-indenyl radical with vinylacetylene. These experimental results are explained through rate constant calculations based on theoretically derived potential energy surfaces.     

Measurements of the hyperfine dimer spectrum for H2-Ne,H2-Ar,H2-Kr by the magnetic beam renosance technique

Measurements are performed on ortho H₂(I = 1, j = 1, vibrational ground state)-X dimers with X = Ne, Ar, Kr; the dimers H₂-X occur in their van der Waals stretch ground state. The dimer end-over-end rotational states (quantum number L) are investigated for L ?2. The rf hyperfine-transition frequencies are measured, 30 ? v ? 600 kHz. Combining our results with scattering data from the Göttingen group, for H₂Ne the full potential could be described with high accuracy. For the other systems, a simple molecular parameter is derived pertaining to the dimer system. As our spectroscopy mainly permits a sensitive probing of the well region, new scattering data are needed to determine accurate model potentials over the full range.     

Crystal structure and interaction with bovine serum albumin of the Cu(I/II) complex [C20H32Cu2I3N4] n

[C₂₀H₃₂Cu₂I₃N₄] _n was synthesized and characterized by elemental analysis, ESI-MS spectrometry, and IR spectra. The crystal structure was determined by X-ray single-crystal diffraction. The binding of the complex with bovine serum albumin (BSA) was studied by fluorescence spectroscopy under simulated physiological conditions. The binding constant (K _b), the number of binding sites (n), and the corresponding thermodynamic parameters ΔH, ΔS, ΔG were calculated based on the van’t Hoff equation. The complex had strong ability to quench the fluorescence from BSA, and the quenching mechanism of this complex to BSA was static quenching. Hydrogen bonds and van der Waals forces are the interactions between the Cu(I/II) complex and BSA. According to the Förster non-radiation energy transfer theory, the binding average distance between the donor (BSA) and the acceptor (Cu(I/II) complex) was obtained. The effect of the complex on the BSA conformation was also studied by using synchronous fluorescence spectroscopy.     

Reactivity Studies of Iridium Pyridylidenes [TpMe2Ir(C6H5)2(C(CH)3C(R)NH] (R=H,Me, Ph)

The reactivity of a series of iridium? pyridylidene complexes with the formula [Tp^Me2Ir(C₆H₅)₂(C(CH)₃C(R)N H] ( 1 a – 1 c ) towards a variety of substrates, from small molecules, such as H₂, O₂, carbon oxides, and formaldehyde, to alkenes and alkynes, is described. Most of the observed reactivity is best explained by invoking 16 e^? unsaturated [Tp^Me2Ir(phenyl)(pyridyl)] intermediates, which behave as internal frustrated Lewis pairs (FLPs). H₂ is heterolytically split to give hydride? pyridylidene complexes, whilst CO, CO₂, and H₂C?O provide carbonyl, carbonate, and alkoxide species, respectively. Ethylene and propene form five‐membered metallacycles with an IrCH₂CH(R)N (R=H, Me) motif, whereas, in contrast, acetylene affords four‐membered iridacycles with the IrC(?CH₂)N moiety. C₆H₅(C?O)H and C₆H₅C?CH react with formation of Ir? C₆H₅ and Ir? C?CPh bonds and the concomitant elimination of a molecule of pyridine and benzene, respectively. Finally the reactivity of compounds 1 a – 1 c against O₂ is described. Density functional theory calculations that provide theoretical support for these experimental observations are also reported.     

Quenching of Li (2P) by H2: potential energy surfaces, conical intersection seam, and diabatic bases

The quenching of Li (1s ²2p; ²P) to Li (1s ²2s; ²S) by H₂ is considered using coupled-cluster and multireference configuration-interaction techniques. C _{2 v} (²A₁, ²B₂) and C _{∞ v} (²Π,²Σ⁺) sections of the 1²A^′ and 2²A^′ potential energy surfaces are determined. The C _{2 v} portion of the 1²A^′−2²A^′ seam of conical intersection is studied. Perhaps the most significant finding is a surprising trifurcation of this seam into a portion with only C _s symmetry and the aforementioned C _{2 v} portion. The adiabatic-to-diabatic state transformation is considered in the vicinity of the seam of conical intersection using both perturbation theory and the dipole moment operator. The ²B₂ section of the 2²A^′ potential energy surface exhibits an exciplex in the general vicinity of the seam of conical intersection. The ²Π section of the 2²A^′ potential energy surface possesses a global minimum lying 1.86kcal/mol below the Li (²P)+H₂ asymptote. A van der Waals-like minimum with C _{∞ v} symmetry was found on the 1²A^′ potential energy surface. Received: 14 August 1998 / Accepted: 20 August 1998 / Published online: 11 November 1998     

l‐Phenyl­alanine–4‐nitro­phenol (1/1)

In the 1:1 adduct formed between l ‐phenyl­alanine and 4‐nitro­phenol [alternative IUPAC name: (2S)‐2‐ammonio‐3‐phenyl­propanoate–4‐nitro­phenol (1/1)], C₉H₁₁NO₂·C₆H₅NO₃, the l ‐phenyl­alanine mol­ecule is in the zwitterionic state. The overall structure is stabilized via strong hydrogen bonding between polar zones and van der Waals inter­actions between non‐polar zones, which alternate with the polar zones.     

Isotope effect in Ni + C2H4 (C2D4) association reaction

The association reactions of atomic nickel with ethene and fully deuterated ethene in carbon dioxide buffer gas at 295 K have been investigated in the pressure range 5–100 torr, using a laser photolysis-laser fluorescence technique. By comparison with results of ab initio quantum chemistry calculations for the complex Ni[C₂H₄], the data are shown to be consistent with reaction on both ground and excited state potential energy surfaces. A simple rate equations treatment is described which shows the form of the pressure dependence of the second-order recombination rate coefficient in this case. Under conditions which are expected to hold for the Ni + C₂H₄ (C₂D₄) reaction, the pressure dependence has the standard Lindemann-Hinshelwood form, with the limiting high pressure rate constant given by an apparent value which reflects the degree to which the participating electronic states are coupled by nonadiabatic transitions. The limiting high pressure behavior of the recombination rate coefficient for Ni + C₂H₄ is not strongly affected by deuterium isotope substitution. However, the effect on the low pressure rate constant is large and consistent with RRKM unimolecular reaction theory. This validates the use of RRKM calculations for estimating the binding energy of the complex from kinetic data. The binding energy of Ni[C₂H₄] is estimated to be 35.2 ± 4.2 kcal mol^?1. © 1994 John Wiley & Sons, Inc.     

Halogen bonding in a series of Br(CF2)nBr–DABCO adducts (n = 4, 6, 8)

Halogen bonding (XB) is a highly‐directional class of intermolecular interactions that has been used as a powerful tool to drive the design of crystals in the solid phase. To date, the majority of XB donors have been iodine‐containing compounds, with many fewer involving brominated analogues. We report the formation of adducts in the vapour phase from a series of dibromoperfluoroalkyl compounds, BrCF₂(CF₂)_n CF₂Br (n = 2, 4, 6), and 1,4‐diazabicyclo[2.2.2]octane (DABCO). Single‐crystal X‐ray diffraction studies of the colourless crystals identified 1,4‐diazabicyclo[2.2.2]octane–1,4‐dibromoperfluorobutane (1/1), C₄Br₂F₈·C₆H₁₂N₂, (I), 1,4‐diazabicyclo[2.2.2]octane–1,6‐dibromoperfluorohexane (1/1), C₆Br₂F₁₂·C₆H₁₂N₂, (II), and 1,4‐diazabicyclo[2.2.2]octane–1,8‐dibromoperfluorooctane (1/1), C₈Br₂F₁₆·C₆H₁₂N₂, (III), each of which displays a one‐dimensional halogen‐bonded network. All three adducts exhibit N…Br distances less than the sum of the van der Waals radii, with butane analogue (I) showing the shortest N…Br halogen‐bond distances yet reported between a bromoperfluorocarbon and a nitrogen base [2.809 (3) and 2.818 (3) Å], which are 0.58 and 0.59 Å shorter than the sum of the van der Waals radii.     

Tailoring a robust Al-MOF for trapping C2H6 and C2H2 towards efficient C2H4 purification from quaternary mixtures

Light hydrocarbon separation is considered one of the most industrially challenging and desired chemical separation processes and is highly essential in polymer and chemical industries. Among them, separating ethylene (C₂H₄) from C2 hydrocarbon mixtures such as ethane (C₂H₆), acetylene (C₂H₂), and other natural gas elements (CO₂, CH₄) is of paramount importance and poses significant difficulty. We demonstrate such separations using an Al-MOF synthesised earlier as a non-porous material, but herein endowed with hierarchical porosity created under microwave conditions in an equimolar water/ethanol solution. The material possessing a large surface area (793 m² g⁻¹) exhibits an excellent uptake capacity for major industrial hydrocarbons in the order of C₂H₂ > C₂H₆ > CO₂ > C₂H₄ > CH₄ under ambient conditions. It shows an outstanding dynamic breakthrough separation of ethylene (C₂H₄) not only for a binary mixture (C₂H₆/C₂H₄) but also for a quaternary combination (C₂H₄/C₂H₆/C₂H₂/CO₂ and C₂H₄/C₂H₆/C₂H₂/CH₄) of varying concentrations. The detailed separation/purification mechanism was unveiled by gas adsorption isotherms, mixed-gas adsorption calculations, selectivity estimations, advanced computer simulations such as density functional theory (DFT), grand canonical Monte Carlo (GCMC) and ab initio molecular dynamics (AIMD), and stepwise multicomponent dynamic breakthrough experiments.

Industrially important C₂H₄ purification from multi-component hydrocarbon mixtures.     

Synthesis and characterization of a Cu(II) complex of 2-benzylmercapto-5-methyl-1,3,4-thiadiazole (C10H10N2S2)

A Cu(II) complex of 2-benzylmercapto-5-methyl-1,3,4-thiadiazole was synthesized and characterized. The crystal structure of the copper complex and the free ligand were determined by single-crystal X-ray diffraction at room temperature: {[Cu(C₁₀H₁₀N₂S₂)₂(Cl)₂], P 1 triclinic, a = 8.1450(2) Å, b = 8.1690(2) Å, c = 10.8180(3) Å, α = 97.4040(12)°, β = 101.6270(11)°, γ = 116.1431(14)°; C₁₀H₁₀N₂S₂ ligand, Pbca orthorhombic, a = 8.7938(7) Å, b = 9.6491(7) Å, c = 25.3552(18) Å}. The metal complex framework consists of discrete units that provide crystalline stability through a network of van der Waals contacts. The Cu(II) is coordinated by two chloride ions and two 2-benzylmercapto-5-methyl-1,3,4-thiadiazole monodentate ligands showing a distorted square planar configuration. Both thiadiazole ligands coordinate through the N atom bonded to the benzylthio substituted C atom.

The FTIR spectroscopic data are consistent with this structural model. Analysis of the magnetic susceptibility from 5 K to room temperature indicates the presence of paramagnetic Cu(II), confirmed by the EPR spectrum.     

Structure of molecular complexes in liquid CO2 solutions of water

The calculated anharmonic frequencies and intensities of simultaneous vibrational transitions in CO₂−H₂O and (CO₂)₂−H₂O hydrogen-bonded complexes are compared with known experimental data. Hydrogen-bonded complexes form in liquid CO₂ solutions of water under normal conditions, unlike the gas phase in which the CO₂ and H₂O molecules are coupled by van der Waals bonds. The majority of these complexes are 2∶1 complexes. N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 375–379, March–April, 1995. Translated from E. Taskaeva     

Interaction potential for He/H2 including the region of the van der waals minimum

The energy of He/H₂ in its ground state is calculated in an ab-initio way using the IEPA PNO method for three different H-H distances, three different angles and for distances between He and the midpoint of H₂ ranging from 3 to 20a₀.A van der Waals minimum of ≈21°K is found for the linear arrangement and a saddle point of ≈14°K for the C_2v geometry. The computed hypersurface is compared with experiment and with the R^?6 term known from perturbation theory. The anisotropy of the potential is much larger than what is predicted asymptotically.     

Synthesis,Crystal Structure,and Characterization of a New Adduct 3-Ammoniumphenyl Sulfone Dihydrogenphosphate Phosphoric Acid [C12H14N2SO2](H2PO4)2H3PO4

Abstract

A new adduct 3-ammoniumphenyl sulfone dihydrogenphosphate phosphoric acid, [C₁₂H₁₄N₂O₂S](H₂PO₄)₂H₃PO₄, has been synthesized by slow evaporation at room temperature using 3-aminophenyl sulfone as the structure-directing agent. The structure, determined by single-crystal X-ray diffraction at 293 K, can be described as inorganic layers built by H₂PO₄ ^? groups and H₃PO₄ molecules, parallel to the (a, c) planes at y = 0.5, between which molecules of the organic group [C₁₂H₁₄N₂O₂S]²⁺ are inserted. In this atomic arrangement, hydrogen bonds and van der Waals interactions between the different species play an important role in the tri-dimensional network cohesion. Solid-state ¹³C and ³¹P MAS NMR spectroscopies are in agreement with the X-ray structure.

[Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental resource: Tables S1 and S2. Figures S1 and S2.]

GRAPHICAL ABSTRACT