Photoionization of the Ar2 dimer

The relative photoionization cross section for Ar₂ was measured in the wavelength region 820–860 Å. The spectrum shows detailed autoionization structure throughout this region with no contribution from direct ionization. The appearance potential of Ar⁺₂ corresponds to 856.5 ± 1.5 Å.     

Three-dimensional Potential Energy Surface and Bound States of the Ar2-Ne Complex

The first three-dimensional interaction potential energy surface (PES) of the Ar₂-Ne complex is developed using the single and double excitation coupled cluster theory with noniterative treatment of triple excitations CCSD(T). The aug-cc-pVQZ basis sets are employed for all atoms, including an additional (3s3p2d2f1g) set of midpoint bond functions. The calculated single point energies are fitted to an analytic two-dimensional potential model at each of seven fixed r_Ar2 values. The seven model potentials are then used to construct the three-dimensional PES by interpolating along (r—r_e) using a sixth-order polynomial. The PES is used in the following rovibrational energy levels calculations. The comparisons of theoretical transition frequencies and spectroscopic constants with the experimental results are given.     

The first synthesis, isolation and X-ray structure of a phosphonium phosphide, (Ph3PMe){[C6H2(CF3)3-2,4,6]2P}

The synthesis of a bulky secondary phosphine, Ar₂PH [Ar=C₆H₂(CF₃)₃-2,4,6], and its use in the first synthesis and isolation of a phosphonium phosphide, (Ph₃PMe)+(Ar₂P)⁻, via the deprotonation of Ar₂PH with a nonstabilised phosphorus ylide, Ph₃P=CH₂, are reported. An X-ray structure of this salt reveals that cations and anions are weakly associated in the solid state through C–HP interactions.     

Konformationsisomerie und isomerisierungen der tetraarylsysteme Ar4Z

The topological properties of tetraaryl systems Ar₄Z with a framework belonging to symmetry group S₄ are investigated considering conformational isomerism and isomerization. All the interconversion paths can be described by 9 mechanisms whose consequences are displayed with graphs and tables.     

A flash photolysis study of the elimination of dinitrogen from trans-(N2)2W(dppe)2; dppe = 1,2-bis-diphenylphosphinoethane

Flash photolysis of trans-(N2)2W(dppe)2 (1) at ?60, ?30, ?10°C, and room temperature indicates that loss of dinitrogen occurs stepwise via the following proposed intermediates. Photodissociation of 1 gives the transient A decaying with k1 ～ 4450 s?1 to the doubly coordinatively unsaturated species [W(dppe)2], B. Further reactions of B are dependent on the type of gas used to saturate the solutions. In N2-saturated media, B is efficiently reconverted into the starting complex 1 via (N2)W(dppe)2], C(N2), kN22 = 450 s?1, which in turn takes up a second molecule of N2, kN23 = 3.7 s?1. In CO-saturated solutions, trans-(CO)2W(dppe)2 is produced as the final product and the corresponding rate constants are kCO2 1500 s?1 for B → C(CO) and kCO3 = 1.14 s?1 for C(CO) → product. In Ar-saturated solvents, B is transformed, again in two steps; kAr2 = 1 s?1 and kAr3 = 0.1 s1?, to products of unknown structure.The different rate constants kN22, kCO2, kAr2 and kN23, kCO3 and kAr3, together the common activation energy of ca. 11 kcal/mol?1 for the three processes A → B, B → C(N2) and C(N2) → 1 suggest that the reactions of B and C occur by SN2-type displacement of coordinated solvent molecules by the incoming ligands.     

Assembly of diverse structural types of organotellurium compounds in the reactions of (4-MeO-C6H4)2TeO with pyridine carboxylic acids

The reactions of Ar₂TeO (Ar = 4-MeO-C₆H₄) with 2-, 3- and 4-pyridine carboxylic acids (LH) afforded different organotelluroxane structural types depending on the stoichiometry of the reactants and the conditions of the reaction. Ar₂Te(L)OH (1a-1c) are formed in a 1:1 reaction of Ar₂TeO with LH in the presence of water. On the other hand a 1:2 reaction under anhydrous conditions leads to the formation of Ar₂TeL₂ (2a-2c). A 2:2 reaction under anhydrous conditions affords the ditelluroxanes Ar₂Te(L)OTe(L)Ar₂ (3a-3c) while tritelluroxanes Ar₂Te(L)OTeAr₂OTe(L)Ar₂ (4a-4c) are formed in 3:2 reactions. Interestingly, 3a-3c are formed in the reaction of 2a-2c with Ar₂TeO. The former can be hydrolyzed to 1a-1c while the latter upon reaction with Ar₂TeO lead to the formation of the tritelluroxanes 4a-4c. Attempts to metalate 2a with PdCl₂(MeCN)₂ leads to a transfer of the carboxylate ligand to palladium affording Ar₂TeCl₂ and PdL₂. X-ray crystal structures of representative examples of the family of 1, 2 and 3 reveal interesting supramolecular structures and the formation of a novel [TeO]₂ structural unit. The latter results from intermolecular secondary Te?O interactions.     

Ab initio determination of the ground-state potential energy curve for Ar2

A totally ab initio potential energy curve for Ar₂ is constructed by adding individually damped dispersion terms to an accurate single configuration self-consistent-field repulsive interaction curve. However, the well depth (77 cm^?1) of our computed curve is significantly less than the experimentaly deduced value (99.4 cm^?1)     

Fast calculation of excited-state potentials for rare-gas diatomic molecules: Ne2 and Ar2

A fast method for obtaining excited-state potentials of rare-gas diatomic molecules is described. Two types of excited orbitals are used: molecular orbitals calculated in the field of a singly charged molecular ion, and atomic orbitals (properly symmetrized) obtained in a similar atomic system. The RPA equations are solved within the manifold of excitations from the highest occupied orbital in each symmetry to the lowest excited orbital of either type in each symmetry. A simple model for estimating the dynamic correlation correction to excitation (and ionization) energies is given. Applications to excited states of Ne₂(^1,3Σ⁺_{g, u}, ^1,3Π_{g, u}) and Ar₂(^1,3Σ⁺_{g, u}) are described. Two-electron integral transformations involve only three orbitals of each symmetry, and the RPA matrices are four-dimensional. The computational effort required for all excited-state potentials adds less than one-tenths (in terms of computer time) to the effort involved in the preliminary ground state Hartree—Fock calculations. The resulting potentials compare favorably with more elaborate CI calculations and give good agreement with spectroscopic and scattering data. Potential curves for the molecular ions are also given.     

Dissociation dynamics of Ar3 in the time-dependent self-consistent field (TDSCF) approximation

The TDSCF approximation is applied to dissociation of Ar₃, which exhibits strong-coupling behavior (efficient internal energy transfer). The TDSCF results are in excellent agreement with those of exact classical dynamics. Combined with earlier findings for weak-coupling cases, this suggests validity of TDSCF for dissociation at all coupling strengths.     

Pyridine and benzonitrile adducts of bis(4-nonafluorobiphenyl)zinc

Treatment of (Ar_F′)₂Zn(OEt₂)₂ (Ar_F′ = 4-C₆F₅C₆F₄) with 2 equiv. of benzonitrile, 4-(phenyl)benzonitrile, 4-(pyrrolyl)benzonitrile, pyridine, 4-(phenyl)pyridine or 4-(pyrrolyl)pyridine in dichloromethane afforded the corresponding adducts (Ar_F′)₂ZnL₂ in near quantitative yield. The 2,2′-bipyridine adduct was prepared similarly. Multinuclear NMR spectroscopy indicated that zinc′s four-coordinate character was maintained in solution. The pyridine complex crystallized from dichloromethane with a solid-state structure free of face-to-face aryl–aryl interactions. In contrast, the 4-(pyrrolyl)pyridine adduct crystallized from both dichloromethane and 1,2-difluorobenzene, with solvent of crystallization, but otherwise essentially identical supramolecular architectures assembled through aryl–aryl synthons, including a face-to-face pentafluorophenyl–pyrrole interaction.     

Syntheses and crystal structures of [Mg(HF)2](SbF6)2 and [Ca(HF)2](SbF6)2: new examples of HF acting as a ligand to metal centres

[Mg(HF)₂](SbF₆)₂ and [Ca(HF)₂](SbF₆)₂ monocrystals were grown from the corresponding hexafluoroantimonates(V) dissolved in anhydrous hydrogen fluoride. [Mg(HF)₂](SbF₆)₂ crystallizes in the space group Pnma (no. 62) with a=1249.1(4) pm, b=1230.2(4) pm, c=699.1(2) pm, V=1.0742(6) nm³, Z=4. Magnesium is octahedrally coordinated by six fluorine atoms from which two belong to two HF molecules. The structure can be represented by alternating rows of magnesium and antimony atoms running parallel to the c-axis. Magnesium atoms are connected by cis bridging Sb(2)F₆ units along the a-axis and by trans bridging Sb(1)F₆ units along the b-axis. In this way a three-dimensional network is formed.[Ca(HF)₂](SbF₆)₂ crystallizes in the space group P2₁/n (no. 14) with a=935.2(3) pm, b=1088.7(3) pm, c=1104.8(3) pm, β=106.697(5)°, V=1.0774(5) nm³, Z=4. The coordination sphere around the calcium atom consists of eight fluorine atoms which define the vertices of an Archimedean antiprism. The two HF molecules directly coordinate the calcium atom and their fluorine atoms are placed in the corners of different square faces of the Archimedean antiprism. The Ca-F(HF) distances are shorter than the Ca-F(Sb) distances. The Sb(1)F₆ and Sb(2)F₆ groups have four equatorial bridging fluorine atoms, while the Sb(3)F₆ groups have only two bridging trans F ligands. The Ca atoms in the [−1,0,1] plane are connected by equatorial F ligands of Sb(1)F₆ and Sb(2)F₆ units, forming a [Ca(SbF₆)⁺]_n layer. These layers are connected by trans bridging Sb(3)F₆ groups. HF molecules occupy the space between these layers and additionally contribute to the connection between the layers by hydrogen bonding.     

trans-Pd(OAc)2(Cy2NH)2 catalyzed Suzuki coupling reactions and its temperature-dependent activities toward aryl bromides

A new catalytic system based on Pd-simple amines for Suzuki coupling reactions of aryl bromides is described. A well-defined air-stable complex, trans-Pd(OAc)₂(Cy₂NH)₂ effectively promotes Suzuki couplings of aryl bromides with a range of aryl boronic acids to give diaryl products in high yields. It also exhibits temperature-dependent activity toward aryl bromides bearing different electronic substituents under reaction conditions.     

[RuCl3(H2O)n]-catalyzed direct arylations

Catalytic amounts of economically attractive [RuCl₃(H₂O)_n] allow for direct arylations via C-H bond functionalization with aryl bromides under phosphine ligand-free reaction conditions. Thereby, a variety of functionalized (hetero)aryl bromides, bearing either electron-withdrawing or electron-releasing substituents, can be employed for direct arylations of pyridine, oxazoline, pyrazole, or ketimine derivatives as pronucleophiles.     

Reductive elimination reaction of rhenium complexes trans-(η-C5Me5)Re(CO)2(chloroaryl)Cl

Thermal reaction of the chloroaryl-chloride complexes trans-(η⁵-C₅Me₅)Re(CO)₂(Ar^Cl)Cl (Ar^Cl = 3-ClC₆H₄, 3-ClC₆H₃(4-Me) and 3,5-Cl₂C₆H₃) in acetonitrile did not interconvert to the cis isomer, instead the complex ReCl(CO)₂(NCMe)₃ and the corresponding 5-Ar^Cl-1,2,3,4,5-pentamethylcyclopentadiene were formed. Similar reductive elimination products were obtained when the starting rhenium complexes were reacted with trimethylphosphite in toluene.     

Photodissociation of the dimer ions Ar+2, Ne+2, and (CO2)+2

The tandem quadrupole photodissociation mass spectrometer has been used to study photodissociation reactions of Ar⁺₂, Ne⁺₂, and (CO₂)⁺₂. The cross sections for photodissociation of Ar⁺₂ exhibited a strong dependence on ion source pressure, varying from 2 × 10 ^?18cm² at 0.1 torr to 6 × 10^?19cm² at 0.5 torr. A large photodissociation cross section (2 × 10^?17cm² for the reaction (CO₂)⁺₂ → CO⁺₂+ CO₂ was observed at the red end of the visible spectrum (580–620 nm) suggesting that this may be an important reaction in CO₂ rich planetary ionspheres such as that of Mars.     

Potassium trifluoroperoxotitanate(IV) trihydrate,K[Ti(O2)F3] · 3H2O

Potassium trifluoroperoxotitanate(IV) trihydrate, K[Ti(O₂)F₃] · 3H₂O, with the peroxide (O₂^2?) being bonded to the Ti(IV) centre in a triangular bidentate manner (C_2ν) as evidenced from the IR and laser Raman spectroscopic studies, has been synthesised from the reaction of a solution of TiO₂in 40% HF with an excess of 30% H₂O₂ and KOH, followed by the addition of aqueous HF to adjust the pH of the reaction solution between 8 and 9.     

The coordination chemistry of (py)2BF2 and related difluoroboron cations

The substitution and decomposition reactions of the difluorobis(pyridine)boron(III) cation, and of several substituted pyridine and other difluoroboron cations (D)₂BF₂⁺, are explored. Donor molecule displacement is greatly accelerated by the presence of electron-withdrawing meta and para pyridine substituents in (substituted pyridine)₂BF₂⁺ cations, and by electron-donating substituents on pyridine when the substituted pyridine is the attacking species. Increased steric hindrance of D in D₂BF₂⁺, and of the attacking base D′, slows or prevents displacement of D by D′. (py)₂BF₂⁺·PF₆⁻ undergoes slow decomposition in acetone, giving initially py·BF₃ and finally py·H⁺·BF₄⁻ as the major fluoroboron species. A second decomposition pathway, giving rise to BF₃OH⁻ and several additional fluorine-containing products, is favoured by the presence of strong bases such as amidines and by the presence of NH and OH bonds. Increased susceptibility to ligand displacement facilitates the synthesis of new fluoroboron cations, but also increases the susceptibility to decomposition.     

FTIR spectra of (HF)2 and (HF)3 species in solid argon at 12K

Condensation of argon/HF mixtures at 12 K revealed sharp new 3825.5 and 3702.0 cm^?1 absorptions which exhibited different growth behaviour on sample warming. Mixed HF/DF samples revealed a single mixed isotopic satellite near the DF counterpart of the former band assigned to (HF)₂ and a group of satellites for the latter band assigned to (HF)₃.     

Enthalpies de formation de l'acide fluorhydrique dans les solutions ternaires HF/HX/H2O (HX  HCl ou H2SO4) I—technique experimentale,methodes de calcul

The apparatus used for the determination of the enthalpies of formation of HF in the ternary solutions HF/HX/H₂O (HX  HCl or H₂SO₄) and the methods of calculation are described.     

Spectroscopic properties of guanidinium zinc sulphate [C(NH2)3]2Zn(SO4)2 and ab initio calculations of [C(NH2)3]2 and HC(NH2)3

Raman and FTIR spectra of guanidinium zinc sulphate [C(NH₂)₃]₂Zn(SO₄)₂ are recorded and the spectral bands assignment is carried out in terms of the fundamental modes of vibration of the guanidinium cations and sulphate anions. The analysis of the spectrum reveals distorted SO₄²⁻ tetrahedra with distinct S–O bonds. The distortion of the sulphate tetrahedra is attributed to Zn–O–S–O–Zn bridging in the structure as well as hydrogen bonding. The CN₃ group is planar which is expressed in the twofold symmetry along the C–N (1) vector. Spectral studies also reveal the presence of hydrogen bonds in the sample. The vibrational frequencies of [C(NH₂)₃]₂ and HC(NH₂)₃ are computed using Gaussian 03 with HF/6-31G* as basis set.