Theoretical evaluation of the nature and strength of the F������F intermolecular interactions present in fluorinated hydrocarbons

The nature, strength and directionality of C?CF···F interactions were theoretically evaluated on all symmetry unique dimers present in the CF₄, C₂F₄ and C₆F₆ crystals and on CF₄, CHF₃, CH₂F₂ and CH₃F model dimers placed in two different geometries. On each dimer, the interaction energy was computed at the MP2/aug-cc-pVDZ level, and also an Atoms in Molecule analysis of the dimer electron density was done to find all intermolecular bonds. The characterization was completed by computing the energy components of the dimer interaction energy, using the SAPT method. The results show that in most dimers found in the CF₄, C₂F₄ and C₆F₆ crystals, there are more than one C?CF···F intermolecular bond and sometimes even a C?CF···?? intermolecular bond. By selecting dimers presenting one C?CF···F bond, the following strength can be estimated for a single C?CF···F bond: ?0.21?kcal/mol in C(sp³) atoms, ?0.25?kcal/mol in C(non-aromatic sp²), ?0.41?kcal/mol in C(aromatic sp²). The interaction energy of the dimer grows almost linearly with the number of C?CF···F bonds present. The relative orientation of the C?CF···F bond affects the bond strength. The SAPT calculations indicate that in collinear dimers, C?CF···F interactions are strongly dominated by the dispersion energetic component, while when in non-collinear conformations the electrostatic component can be as important as the dispersion one.     

The microwave spectrum and structure of 1,1,1,3,3,3-hexafluoropropane,freon R236fa

The microwave spectra of three isotopic species of 1,1,1,3,3,3-hexafluoropropane (R236fa) (CF₃CH₂CF₃, ¹³CF₃CH₂CF₃ and CF₃¹³CH₂CF₃) were observed in the region from 4.5 to 18 GHz using a molecular beam Fourier transform microwave spectrometer (MB-FTMW). The rotational and centrifugal distortion constants were determined. The r_s (C–C) bond length and bond angle (C–C–C) of the molecule were determined to be 1.56(5) and 109(3) Å, respectively. The ab initio calculation of R236fa was executed at the MP2/6-31G(d,p) level. Comparison of the bond length and bond angle of R236fa with those in the other fluoropropanes revealed trends for the C–C bond length and CCC angle, depending on the number of fluorine atoms attached to the central carbon. A similar idea had been noted by Mack et al. from the electron diffraction studies of fluoropropanes.     

The reaction of 2′ 2′ 3′ 3′-tetrafluoropropyl-5-iodo-3-oxaoctafluoropentane sulfonate with dimethylsulfoxide and determination of the crystal structure of one of the products

The title reaction gave three known compounds (2, 3 and 4) and two new compounds, CH₃SCH₂(CF₂)₂H (5) and I(CF₂)₂O(CF₂)₂SO₃⁻S+(CH₃)₃ (6). The structure of 6 was confirmed by X-ray diffraction analysis. The crystals of 6 belong to monoclinic space group P2₁/C with a = 9.399, b = 15.651, c=10.934Å, β = 94.80° and z = 4. The structure was solved by heavy-atom method and refined by block-diagonal matrix least-squares procedure to a final R of 0.054 for 1999 independent observed reflexions. The S C bonds around the sulphur atom in trimethylsulphonium are pyramidal with the bond lengths of 1.814 Å, 1.800Å and 1.818 Å and the bond angles C-S-C of 101.06°, 101.52° and 102.53°. The distances of the sulphur atom in trimethylsulphonium to three oxygen atoms in the sulphonate radical are 3.79 Å, 3.64 Å and 3.34 Å respectively. These distances are out of the range of the normal S-O bond length. The structure consists of trimethylsulphonium cations and 5-iodo-3-oxaoctafluoropentane-sulphonate anions.     

Estimation of rate constants for hydrogen atom abstraction by OH radicals using the C?H bond dissociation enthalpies: Haloalkanes and haloethers

We propose a semiempirical procedure for the estimation of the rate constants for hydrogen atom abstraction reactions of OH radicals with haloalkanes and haloethers. Our procedure is derived from the collision theory based kinetic equation, which was originally proposed by Heicklen (Int. J. Chem. Kinet. 1981, 13 , 651). This equation provides the estimates for the rate constants of hydrogen abstraction from the C? H bond dissociation enthalpy for each potential hydrogen atom abstraction site. We reparameterized the equation and then applied this procedure to a series of haloalkane and haloether molecules. The results obtained from the new equations are found to be quite satisfactory. In addition, we also report highly reliable calculated values of the C? H bond dissociation enthalpies for six environmentally important haloether molecules (CH₂FOCH₂F, CHF₂CF₂OCH₂CF₃, CF₃CH₂OCH₂CF₃, CF₃CF₂CH₂OCHF₂, CHF₂OCF₂CHFCl, and CHF₂OCHClCF₃). © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 130–138, 2003     

A gas-phase electron diffraction study op the molecular structure of 1,1,1,2-tetrafluoroethane

The molecular structure of 1,1,1,2-tetrafluoroethane is studied using gas-phase electron diffraction data collected on the Balzers KDG2 instrument. Effective least-squares refinement of the geometry is achieved with values for vibrational amplitudes transferred from normal coordinate calculations on related molecules. The following values for the main independent geometrical parameters are obtained (r_a values with e.s.d. in parentheses): C-C = 1.501(4) Å, C-H = 1.077 (15) Å, C-F(CH₂F) = 1.389(6) Å, C-F(CF₃) = 1.334 (2) Å, ∠CCH= 106.1(12)°, ∠CCF(CH₂F)= 112.3(4) Å, ∠CCF(CF₃)= 110.4(2). Other angles are ∠FCF = 108.6 (2)° and ∠FCH = 111.4(15)°, with ∠HCH constrained at 109.4°. The r_a bond lengths of all the fluoroethanes are compared.     

Thermal decomposition of some silver(I) carboxylates under nitrogen atmosphere

The thermal decomposition reactions of CH₃CH₂C(CH₃)₂COOAg (1), (CH₃)₃SiCH₂COOAg (2), CF₃COOAg (3), (CH₃)₃CCOOAg (4), C₂H₅COOAg (5), C₃F₇COOAg (6), C₆F₁₃COOAg (7) and (CF₂)₃(COOAg)₂ (8) were studied in N₂ atmosphere using thermogravimetry (TG), derivative thermogravimetry and differential thermal analysis. Characterized compounds decomposed in one- or multi-step processes with metallic silver formation in the range 215–465 °C. TG-IR studies of gases evolved during thermolysis revealed products of decomposition, such as carboxylic acids, CO₂ and recombination reactions.     

Thulium(III) trifluoroacetates Tm(CF3COO)3 · 3H2O and Tm2(CF3COO)6 · 2CF3COOH · 3H2O: Synthesis and crystal structure

Thulium trifluoroacetate compounds have been synthesized, Tm(CF₃COO)₃ · 3H₂O (I) and Tm₂(CF₃COO)₆ · 2CF₃COOH · 3H₂O (II). The structure of I has been refined by the Rietveld method on the basis of the structural data for Cd(CF₃COO)₃ · 3H₂O. The structure of II has been solved in a single-crystal X-ray diffraction study. Compound I has been studied by thermal analysis. Crystals of I and II are monoclinic: for I a = 9.062(2) Å, b = 18.678(3) Å, c = 9.687(2) Å, β = 113.93(1)°, Z = 2, space group P2₁/c, R ₁ = 0.062; for II a = 8.560(4) Å, b = 19.866(5) Å, c = 20.813(7) Å, β = 101.69(4)°, Z = 8, space group C2/c, R ₁ = 0.0392. In the molecular structure of I, thulium atoms are bonded in pairs through four bridging trifluoroacetate anions to form dimers. The coordination polyhedron of the thulium atom also includes the three O atoms of the water molecules and the O atom of the monodentate trifluoroacetate group; the coordination number of the thulium atom is eight. In the chain structure of II, there are two crystallographically independent thulium atoms with coordination numbers 8 and 9. The coordination polyhedra of the Tm(1) and Tm(2) atoms are a distorted monocapped tetragonal antiprism and a distorted tetragonal antiprism, respectively. The Tm-O bond lengths are in the range 2.28(1)–2.85(2) Å. The thulium atoms are bound into chains through carboxylate groups. These chains are linked into layers through hydrogen bonds.     

Volatile dimethylgold(III) β-iminovinylthionates: Synthesis,structure, and properties

Volatile dimethylgold(III) β-iminovinylthionates, (CH₃)₂Au(CH₃CSCHC(NH)CH₃) (I) and (CH₃)₂Au(CF₃CSCHC(NH)CH₃) (II), were studied. For complexes I and II, the synthesis is described and data from elemental analysis, IR and UV/Vis spectra, DTA, and X-ray diffraction are given. The structures of I and II are composed of monomeric complexes combined into polymeric stack-type associates. The distorted square environment of gold is formed by sulfur and nitrogen atoms of the chelating ligand and two carbon atoms of the methyl groups. For complex I, the average Au-S bond length is 2.260 Å, the Au-N bond length is 2.137 Å, and the chelate angle SAuN is 94.1°; for II, these values are 2.355 Å, 2.088 Å, and 93.7°, respectively.     

A study of the structure and properties of mixed-ligand Cu(II) complexes with hexafluoroacetylacetone and methyl-, phenyl-ketoimines

The synthesis and X-ray single crystal study of two mixed-ligand Cu(II) complexes are performed: (CH₃C(NCH₃)CHC(O)CH₃)(CF₃C(O)CHC(O)CF₃)Cu (1) (space group P2₁/c, a = 7.0848(12) Å, b = 17.854(3) Å, c = 11.837(2) Å, β = 100.495(6)°, V = 1472.4(4) ų, Z = 4), (CH₃C(NC₆H₅)CHC(O)CH₃)· (CF₃C(O)CHC(O)CF₃)Cu (2) (space group P-1, a = 9.1119(4) Å, b = 9.6954(4) Å, c = 11.1447(6) Å, α = 113.784(2)°, β = 92.383(2)°, γ = 95.402(2)°, V = 893.52(7) ų, Z = 2). The structures are molecular, formed from neutral mixed-ligand copper complexes. The central copper atom has the (3O+N) coordination environment with average Cu-O distances of 1.948 Å and Cu-N of 1.932 Å; the chelate O-Cu-N angle (average) is 94.0°. In the structures, the complexes are linked into dimeric associates with Cu…Cu distances of 3.197 Å (for 1) and 3.246 Å (for 2). The volatility of mixed-ligand complexes 1 and 2 is in between of that of the starting homo-ligand complexes.     

A density functional theory study of dimers of hydrophosphoryl compounds and proton transfer in them

The structures of dimers of several types of dimethylphosphinous acid (CH₃)₂POH and dimethylphosphine oxide (CH₃)₂P(O)H and dimers of the corresponding perfluorinated derivatives (CF₃)₂POH and (CF₃)₂P(O)H were studied in detail by density functional theory with the PBE gradient-corrected functional and the TZ2p basis set. Fairly strong dimeric associates (2.50–10.5 kcal/mol) were shown to form thanks to O-H···O, O-H···P, and C-H···O H-bonds and dipole-dipole interactions of polar phosphoryl groups P → O of two monomer molecules. The existence of C-H···O and the absence of P-H···O H-bonds in (CH₃)₂P(O)H dimers was substantiated by an AIM (atoms in molecules) analysis of their structures according to Bader. The reaction coordinates were calculated for synchronous transfer of two protons in (CH₃)₂POH and (CF₃)₂P(O)H dimers. Both rearrangements were shown to occur via symmetrical six-membered planar transition states with activation barriers of less than 20 kcal/mol, which was much lower than for intramolecular transfer in the corresponding monomers (47 kcal/mol for the (CH₃)₂P(O)H → (CH₃)₂POH pair). The tautomeric transitions between the phosphinous acid and phosphine oxide forms observed experimentally in nonpolar media under mild conditions in the absence of molecules that could act as proton carriers were shown to proceed as bimolecular reactions with the intermediate formation of the corresponding dimers.     

氰化物与吡咯复合物氢键强度的理论研究

The R-C≡N…pyrrole (R=H, CH3, CH2F, CHF2, CF3, NH2, BH2, OH, F, CH2Cl, CHCl2, CCl3, Li, Na) complexes were considered as the simple sample for measure of hydrogen bonding strength. Density functional theory B3LYP/6-311 G^** level was applied to the optimization of geometries of complexes and monomers. Measure of hydrogen bonding strength based on geometrical and topological parameters, which were derived from the AIM theory, was analyzed. Additionally, natural bond orbital (NBO) analysis and frequency calculations were performed.From the computation results it was found that the electronic density at N-H bond critical points was also strictly correlated with the hydrogen bonding strength.     

Kinetics and mechanism of atmospheric reactions of partially fluorinated alcohols

Gas-phase reactions typical of the Earth’s atmosphere have been studied for a number of partially fluorinated alcohols (PFAs). The rate constants of the reactions of CF₃CH₂OH, CH₂FCH₂OH, and CHF₂CH₂OH with fluorine atoms have been determined by the relative measurement method. The rate constant for CF₃CH₂OH has been measured in the temperature range 258–358 K (k = (3.4 ± 2.0) × 10¹³exp(?E/RT) cm³ mol^?1 s^?1, where E = ?(1.5 ± 1.3) kJ/mol). The rate constants for CH₂FCH₂OH and CHF₂CH₂OH have been determined at room temperature to be (8.3 ± 2.9) × 10¹³ (T = 295 K) and (6.4 ± 0.6) × 10¹³ (T = 296 K) cm³ mol^?1 s^?1, respectively. The rate constants of the reactions between dioxygen and primary radicals resulting from PFA + F reactions have been determined by the relative measurement method. The reaction between O₂ and the radicals of the general formula C₂H₂F₃O (CF₃CH₂? and CF₃?HOH) have been investigated in the temperature range 258–358 K to obtain k = (3.8 ± 2.0) × 10⁸exp(?E/RT) cm³ mol^?1 s^?1, where E = ?(10.2 ± 1.5) kJ/mol. For the reaction between O₂ and the radicals of the general formula C₂H₄FO (? HFCH₂O, CH₂F?HOH, and CH₂FCH₂?) at T = 258–358 K, k = (1.3 ± 0.6) × 10¹¹exp(?E/RT) cm³ mol^?1 s^?1, where E = ?(5.3 ± 1.4) kJ/mol. The rate constant of the reaction between O₂ and the radicals with the general formula C₂H₃F₂O (?F₂CH₂O, CHF₂?HOH, and CHF₂CH₂?) at T = 300 K is k = 1.32 × 10¹¹ cm³ mol^?1 s^?1. For the reaction between NO and the primary radicals with the general formula C₂H₂F₃O (CF₃CH₂? and CF₃?HOH), which result from the reaction CF₃CH₂OH + F, the rate constant at 298 K is k = 9.7 × 10⁹ cm³ mol^?1 s^?1. The experiments were carried out in a flow reactor, and the reaction mixture was analyzed mass-spectrometrically. A mechanism based on the results of our studies and on the literature data has been suggested for the atmospheric degradation of PFAs.     

Gas phase molecular structure of bis(trifluoromethyl). mercury (CF3)2 Hg

The molecular structure of bis(trifluoromethyl)mercury has been determined by electron diffraction of gases. The best agreement between experiment and model was obtained for freely rotating CF₃ groups and the following geometric parameters (r°_α values): C-F = 1.345(3) Å, Hg-C = 2.101(5) Å and <FCF = 106.8°(0.2). The effect of CH₃/CF₃ substitution on the Hg-C bond length is discussed.     

Gas-phase electron diffraction studies of the molecular structures of pentafluoroethane,C2F5H,and monofluoroethane,C2H5F

The molecular structures of C₂F₅H and C₂H₅F have been studied using gas-phase electron diffraction data collected on the Balzers KDG2 instrument. The following values for the main independent geometrical parameters were obtained (r_a values with e.s.d. in parentheses): in C₂F₅H, C-C = 1.525(4) Å, C-F(CHF₂) = 1.347 Å, C-F(CF₃) = 1.327 Å [C-F(av.) = 1.335(2) Å], ∠CCF(av.) = 110.0(2)°; in C₂H₅F, C-C = 1.502(5) Å, C-F = 1.397(4) Å, C-H = 1.097(2) Å. ∠CCF = 110.4(2)°, ∠CCH(av.) = 113.6(4)°. Evidence is presented to show that the electron diffraction data for C₂H₅F are not compatible with values for the bond angles deduced spectroscopically.     

Rate constants for the gas-phase reactions of Cl atoms with a series of hydrofluorocarbons and hydrochlorofluorocarbons at 298 ± 2 K

A relative rate method has been used to determine rate constants for the gas-phase reactions of a series of hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) at 298 ± 2 K and atmospheric pressure of air. Based on a rate constant for the reaction of the Cl atom with CH₄ of (1.0 ± 0.2) ? 10^?13 cm³ molecule^?1 s^?1 at 298 K, the following Cl atom reaction rate constants (in units of 10^?15 cm³ molecule^?1 s^?1) were obtained: CH₃F, 340 ± 70; CH₃CHF₂, 240 ± 50; CH₂FCl, 110 ± 25; CHFCl₂, 21 ± 4; CHCl₂CF₃, 14 ± 3; CHFClCF₃, 2.7 ± 0.6; CH₃CFCl₂, 2.4 ± 0.5; CHF₂Cl, 2.0 ± 0.4; CH₂FCF₃, 1.6 ± 0.3; CH₃CF₂Cl, 0.37 ± 0.08; and CHF₂CF₃, 0.24 ± 0.05. These Cl atom reaction rate constants are compared with literature data and with the corresponding OH radical reaction rate constants. © John Wiley & Sons, Inc.     

Experimental and chemical kinetic study of the pyrolysis of trifluoroethane and the reaction of trifluoromethane with methane

A detailed reaction mechanism is developed and used to model experimental data on the pyrolysis of CHF₃ and the non-oxidative gas-phase reaction of CHF₃ with CH₄ in an alumina tube reactor at temperatures between 873 and 1173 K and at atmospheric pressure. It was found that CHF₃ can be converted into C₂F₄ during pyrolysis and CH₂CF₂ via reaction with CH₄. Other products generated include C₃F₆, CH₂F₂, C₂H₃F, C₂HF₃, C₂H₆, C₂H₂ and CHF₂CHF₂. The rate of CHF₃ decomposition can be expressed as 5.2×10¹³ [s−1] e−295[kJ mol−1]/RT. During the pyrolysis of CHF₃ and in the reaction of CHF₃ with CH₄, the initial steps in the reaction involve the decomposition of CHF₃ and subsequent formation of CF₂ difluorocarbene radical and HF. It is proposed that CH₄ is activated by a series of chain reactions, initiated by H radicals. The NIST HFC and GRI-Mech mechanisms, with minor modifications, are able to obtain satisfactory agreement between modelling results and experimental data. With these modelling analyses, the reactions leading to the formation of major and minor products are fully elucidated.     

Coordination polymer of Ag trifluoroacetate with 2-methylpyrazine: Synthesis and structure of [Ag(CF3CO2)(2-Me-Pyz)]

The [Ag(CF₃CO₂)(2-Me-Pyz)] complex (where 2-Me-Pyz is 2-methylpyrazine) was synthesized and its structure was determined. The crystals are monoclinic, space group P2₁/n, a = 12.440(2) Å, b = 2.605(3) Å, c = 12.646(3) Å, β = 95.95(3)°, V = 1972.3(7) ų, ρ = 2.122 g/cm³, Z = 8. The structure consists of the polymer zigzag chains of [Ag(C₅H₆N₂)] _? ^∞ united into a three-dimensional framework through (CF₃CO₂)^? anions.     

Synthesis and crystal structure of the mixed-ligand coordination silver polymer [Ag(CH<Subscript>3</Subscript>SO<Subscript>3</Subscript>)(2,3-Et<Subscript>2</Subscript>Pyz)] · H<Subscript>2</Subscript>O

The coordination polymer [Ag(CH₃SO₃)(2,3-Et₂Pyz)] · H₂O (2,3-Et₂Pyz is diethylpyrazine, C₈H₁₂N₂) was synthesized and its crystal structure was determined. The crystals are triclinic, space group P \(\bar 1\), a = 7.212(1)Å, b = 8.446(1) Å, c = 11.394(1) Å, α = 107.58(1)°, β = 100.35(1)°, γ = 99.52(1)°, V = 632.7(1) ų, ρ_calc = 1.875 g/cm³, Z = 2. In this structure, pairs of silver atoms are linked by bridging methanesulfonate anions CH₃SO ₃ ^? into dimeric units Ag₂(CH₃ SO₃)₂. The distance between the silver atoms in this dimer is 5.16 Å.In addition to two oxygen atoms of the CH₃SO₃ ligands, the Ag⁺ ion coordinates two nitrogen atoms of the neutral ligand 2,3-Et₂Pyz. As a result, polymeric chains [Ag(Et₂Pyz)] _∞ ⁺ are formed along the [100] vector, which are associated in pairs by methanesulfonate anions into infinite columns. Water molecules form H-bonds with oxygen atoms of adjacent CH₃SO ₃ ^? anions.     

Crystal and molecular structures of bis(2,2,6,6-tetramethyl-3-methylaminoheptan-5-onate) copper(II) and nickel(II)

Two bis-chelates M(tmih)₂ (M = Cu(II), Ni(II), tmih = (CH₃)₃C(NCH₃)CHCOC(CH₃)₃)^? are synthesized and their crystal structures are determined using XRD (Bruker APEX-II diffractometer with a CCD detector, λMoK _α, λCuK _α, graphite monochromator, T = 240(2) K and 296(2) K): Cu(tmih)₂ (I) (space group P2₁/c, a = 12.9670(8) Å, b = 18.4921(9) Å, c = 11.0422(6) Å, β = 93.408(4)°, V = 2643.1(3) ų, Z = 4) and Ni(tmih)₂ (II) (space group P2₁/c, a = 12.810(2) Å, b = 18.529(2) Å, c = 11.243(2) Å, β = 91.959(7)°, V = 2667.1(6) ų, Z = 4). The complexes are isostructural; the coordination polyhedron of metal atoms is a flattened tetrahedron formed from two O atoms (Cu-O of 1.901(2) Å, 1.892(2) Å, Ni-O of 1.845(2) Å, 1.833(2) Å) and two N atoms (Cu-N of 1.976(3) Å, 1.972(3) Å, Ni-N of 1.911(2) Å, 1.920(2) Å) of the ligand; the chelate OMN angles (M = Cu(II), Ni(II)) are in the 87.4–93.1° range; the OMO and NMN angles are 162.2° and 167.2° in I, 171.1° and 173.2° in II. The complexes have the molecular structures formed from isolated molecules bonded by van der Waals interactions. Using a quantum chemical hybrid M06 method, the structures of copper(II) chelates with the H, CH₃, CH₂CH₃, CH(CH₃)₂, and C(CH₃)₃ substituents at the nitrogen atom are calculated. Found that with a bulky substituent at the nitrogen atom, the formation of chelates is hindered due to the intraligand repulsion between the atoms of this substituent and the tert-butyl group.     

Two Modifications of Y2Piv6(Hpiv)6 crystals: Synthesis and structures

Crystals of two modifications of yttrium pivalate solvate Y₂Piv₆(HPiv )₆(HPiv = (CH₃)₃CCOOH) are synthesized and studied by single-crystal X-ray diffraction analysis. The 3α-modification crystallizes in the monoclinic system, a = 16.394(2) Å, b = 11.948(4) Å, c = 20.352(3) Å, β = 108.73(3)°, Z = 4, space group P2₁/n, R ₁ = 0.105. Crystals of the β-modifications are also monoclinic, a = 21.617(4) Å, b = 36.559(4) Å, c = 29.930(4) Å, β = 104.40(2)°, Z = 12, space group P2₁/c, R ₁ = 0.050. The molecular structures of crystals of the α-and β-modifications consist of the Y₂(μ₂-Piv)₄(Piv)₂(HPiv)₆ dimers. The Y atoms with a distorted antiprismatic coordination surrounding of the O atoms (Y-O 2.23–2.53 Å) are linked by four bridging bidentate pivalate anions and form the structural fragment shaped into a distorted lantern. Monodentate Hpiv molecules participate in the formation of intramolecular hydrogen bonds with Piv ligands. Crystal structures of the α-and β-modifications differ in packing of the Y₂Piv₆(HPiv)₆ dimers and in centrosymmetric nature of the dimers in the structure of the α-modification.