Simultaneous electron diffraction and mass-spectrometric study of the structure of the MoF5 molecule

Electron diffraction data for the MoF₅ molecule are analyzed in terms of an r_a structure. Three models of the geometrical structure, which have D_3h, C_4v, and C_2v symmetry, are considered. It is confirmed that a distorted bipyramid of C_2v symmetry is the best model that is in agreement with experimental electron diffraction data. The model has three different types of nuclear Mo-F distances: r_α(Mo-F_1eq) = 1.720(5) Å, r_α(Mo-F_2eq) = 1.826(7) Å, r_α(Mo-F_ax) = 1.825(7) Å. The bond angle between the pseudoaxial bonds is 168.1(0.6)?, and the angle between the Mo-F_2eq pseudoequatorial bonds is 122.6(0.8)?. The r_a(Mo-F_leq) and r_a(Mo-F_2eq) distances differ significantly. Possible reasons for this are discussed.     

Spatiotemporal dynamics of an NPZ model with prey-taxis and intratrophic predation

Nonlinear Dynamics - Spatiotemporal dynamics of plankton community and the nutrients in a vertical column of water are considered. In this paper, the temporal model is first researched to determine...     

Molecular structure of TmCl3 by synchronous electron diffraction and mass spectrometric experiment

The molecular structure of lanthanide trihalides has been discussed since 1959, when the first electron diffraction data were obtained for LaHal₃ and NdHal₃ [1]. The diffraction pattern was initially interpreted [1] with the assumption that the molecules have a planar structure. Later, more elaborate procedures for recording and interpreting electron diffractograms led to structure determination for three lanthanide trifluorides (PrF₃, GdF₃, HoF₃) [2], six trichlorides (LaCl₃, PrCl₃, GdCl₃, TbCl₃, H0Cl₃, LuCl₃) [3-7], three tribromides (LaBr₃, GdBr₃, LuBr₃) [8, 9], and five triiodides (Prl₃, Ndl₃, Gdl₃, Lul₃ [10], Cel₃ [11]). It was found that all of these molecules have an effective nonplanar configuration. An attempt was made to trace the tendencies of bond angle variation for the equilibrium configuration in the series LaHal₃-LuHal₃ and LnF₃-LnI₃ [12]. This molecular structure study performed on TmCl₃ is aimed to clarify details of molecular structure variation in the second half of the LnCl₃ series. Translated from Zhumal Struktumoi Khimii, Vol. 41, No. 1, pp. 182-186, January–February, 2000.     

Energies of the gas-phase deprotonation of nitro-substituted benzenesulfonic and benzoic acids: The role of the conformation isomerism of sulfonic acids

The Gibbs energies of deprotonation Δ_r G ₂₉₈ ^○ of gaseous benzoic acid (BA), benzenesulfonic acid (BSA) and their six mono-, di-, and trinitro-substituted derivatives are calculated by means of B3LYP/cc-pVTZ and MP2/6-311++G**. The dependences of Δ_r G ₂₉₈ ^○ on the number and the position of nitro groups in an aromatic ring are revealed, as is the possibility of intramolecular hydrogen bond (IHB) formation in ortho-substituted acids. It is found that the deprotonation of conformers of ortho-nitro-substituted BSA without IHBs requires less energy (by 4–5 kcal/mol) than for conformers with IHBs. It is shown that the Δ_r G ₂₉₈ ^○ values for substituted BA are ～22 kcal/mol higher than the corresponding values for substituted BSA. A trend of diminishing Δ_r G ₂₉₈ ^○ for nitro-substituted acids is observed when the number of nitro groups is increased, and di- and trinitro-substituted BSA may therefore be considered superstrong acids.     

The Effect of Intramolecular Hydrogen Bond Type on the Gas-Phase Deprotonation of ortho-Substituted Benzenesulfonic Acids. A Density Functional Theory Study

Structural factors have been identified that determine the gas-phase acidity of ortho-substituted benzenesulfonic acid, 2-XC₆H₄–SO₃H, (X = –SO₃H, –COOH, –NO₂, –SO₂F, –C≡N, –NH₂, –CH₃, –OCH₃, –N(CH₃)₂, –OH). The DFT/B3LYP/cc-pVTZ method was used to perform conformational analysis and study the structural features of the molecular and deprotonated forms of these compounds. It has been shown that many of the conformers may contain anintramolecular hydrogen bond (IHB) between the sulfonic group and the substituent, and the sulfonic group can be an IHB donor or an acceptor. The Gibbs energies of gas-phase deprotonation Δ_rG⁰₂₉₈ (kJ mol^–1) were calculated for all compounds. It has been set that in ortho-substituted benzenesulfonic acids, the formation of various types of IHB is possible, having a significant effect on the Δ_rG⁰₂₉₈ values of gas-phase deprotonation. If the –SO₃H group is the IHB donor, then an ion without an IHB is formed upon deprotonation, and the deprotonation energy increases. If this group is an IHB acceptor, then a significant decrease in Δ_rG⁰₂₉₈ of gas-phase deprotonation is observed due to an increase in IHB strength and the A⁻ anion additional stabilization. A proton donor ability comparative characteristic of the –SO₃H group in the studied ortho-substituted benzenesulfonic acids is given, and the Δ_rG⁰₂₉₈ energies are compared with the corresponding values of ortho-substituted benzoic acids.     

Molecular structure and conformations of para-methylbenzene sulfonamide and ortho-methylbenzene sulfonamide: gas electron diffraction and quantum chemical calculations study

The molecular structure and conformational properties of para-methylbenzene sulfonamide (4-MBSA) and ortho-methylbenzene sulfonamide (2-MBSA) have been studied by gas electron diffraction (GED) and quantum chemical methods (B3LYP/6-311+G** and MP2/6-31G**). Quantum chemical calculations predict the existence of two conformers for 4-MBSA with the S-N bond perpendicular to the benzene plane and the NH2 group either eclipsing or staggering the S-O bonds of the SO2 group. Both conformers possess CS symmetry. The eclipsed form is predicted to be favored by DeltaE = 0.63 kcal/mol (B3LYP) or 1.00 kcal/mol (MP2). According to the calculations, the S-N bond in 2-MBSA can possess planar direction opposite the methyl group (phi(C2C1SN) = 180 degrees ) or nonplanar direction (phi(C2C1SN) approximately 60 degrees ). In both cases, the NH2 group can adopt eclipsed or staggered orientation, resulting in a total of four stable conformers. The nonplanar eclipsed conformer (C1 symmetry) and the planar eclipsed form (CS symmetry) are predicted to be favored. According to the GED analysis, the saturated vapor over solid 4-MBSA at T = 151(3) degrees C consists as mixture of the eclipsed (78(19) %) and staggered (22(19) %) forms. The saturated vapor over solid 2-MBSA at T = 157(3) degrees C consists as a mixture of the nonplanar eclipsed (69(11) %) and planar eclipsed (31(11) %) forms.     

The composition of saturated and superheated vapors and molecular structure of Lu(C5O2HF6)3

The molecular structure of lutetium tris-hexafluoroacetylacetonate Lu(hfa)₃ was studied in a synchronous electron diffraction and mass spectrometric experiment and quantum-chemically by the HF and DFT/B3LYP methods. Saturated vapor over Lu(hfa)₃ was found to be oligomerized to a substantial extent. The mass spectrum of saturated Lu(hfa)₃ vapor was studied over the temperature range 76–100°C; it contained peaks of ions with one to three metal atoms. The peak of the highest intensity corresponded to the M₂L ₅ ⁺ stoichiometry. It was found in experiments with vapor superheating in a double two-temperature effusion cell that oligomeric forms disappeared above 150°C, whereas the decomposition of the monomeric form became noticeable above 250°C. The results obtained in theoretical and experimental studies allowed us to determine the structure of the Lu(hfa)₃ molecule.     

Gas-phase structure and conformational properties of 3,3,6,6-tetramethyl-1,2,4,5-tetroxane

The geometric structure and conformational properties of 3,3,6,6-tetramethyl-1,2,4,5-tetroxane (diacetone diperoxide) have been studied by gas electron diffraction and quantum chemical calculations (MP2 and B3LYP methods with 6-31G(d,p) and 6-311+G(2df,p) basis sets). The molecule possesses a chair conformation with C2h symmetry and the following geometric parameters for the six-membered ring (rh1 values) have been determined: O-O = 1.463(5) A, C-O = 1.432 (4) A, O-C-O = 108.2(7) degrees, C-O-O = 107.7(4) degrees, phi(C-O-O-C) = 63.7(4) degrees, and phi(O-O-C-O) = -63.9(4) degrees. A small contribution of less than 3.5% of a twist conformer with C2 symmetry cannot be excluded. Quantum chemical calculations predict a contribution between 1 and 2%. Additional calculations for the parent compound 1,2,4,5-tetroxane (diformaldehyde diperoxide) demonstrate that methyl substitution at the carbon atoms has a minor effect on the ring geometry but a strong effect on the conformational properties. Methyl substitution reduces the energy difference between twist and chair conformers by more than 5 kcal/mol.