G. V. Girichev

Structure and Energetics of β-Diketonates. XII. Structure of Lanthanide tris-Dipivaloylmethanates for Er(thd)3 Used as an Example

A simultaneous electron diffraction and mass spectroscopic study of saturated vapors of erbium tris-dipivalylmethanate has revealed that at 136(5)°C, the vapor consists solely of Er(thd)3 molecules. Electron diffraction data may be described by two alternative models (of C_3 and D_3 symmetry), for which ra, rg, and rα structural parameters have been determined. D3 symmetry is recognized to be preferable for free Er(thd)3 molecules. The main structural parameters of the model are rα (Er − O) 2.218(5), rα (O − C) 1.279(5), rα (C − Cr) 1.404(6), rα (C − Ct) 1.512(3), rα(Ct − Cm) 1.542(5), rα (rm Cm− H) 1.804(4) Å, The ErO 75.0(0.4)°. The ErO6 coordination polyhedron has a structure close to an antiprism. A rotational angle of the O–O–O trigonal face relative to the position in a regular prism is 20.7(0.8)°. Possible reasons for the differences in the structure of Er(thd)3 molecules in the gas phase and crystal are discussed.

The structure of a thiadiazole-containing expanded heteroazaporphyrinoid determined by gas electron diffraction and density functional theory calculations.

The molecular structure of a macrocycle with a 24-membered ring, a thiadiazole-containing expanded heteroazaporphyrinoid, has been, for the first time, directly characterised by a synchronous gas electron diffraction and mass spectrometric experiment and DFT calculations; the molecule has the equilibrium structure of C(3h) symmetry with a planar macrocycle.

The structure of oxotitanium phthalocyanine: a gas-phase electron diffraction and computational study

The gas-phase molecular structure of oxotitanium phthalocyanine (TiOPc) has been studied by a synchronous gas electron diffraction and mass spectrometric experiment, and density functional theory calculations using the B3LYP hybrid method and cc-pVTZ basis sets. The molecule has an equilibrium structure of C4v symmetry with a convex macrocycle. The titanium atom is out-of-the-plane of the four central nitrogen atoms and forms a square pyramid with them, with the following parameters: r(Ti-N)=2.090(5) A, r(NN)=2.813(9) A (the side of the pyramid base), z(Ti)-z(N)=0.614 A (the height of the pyramid). Compared to solid-state crystal structures, the Ti-O distance in gas-phase TiOPc is shortened and the Ti-N distance is elongated, which can be attributed to significant intermolecular interaction in the crystals.

Structure and vibrational frequencies of aluminum trifluoride and gallium trifluoride

AlF3 and GaF3 were studied by gas-phase diffraction. These molecules have D/sub 3h/ symmetry. Treatment of the experimental data in terms of vibrational potential function parameters gave the equilibrium internuclear distances and the frequency of the fully symmetrical vibration.

Gas electron diffraction and quantum chemical studies of the molecular structure of 2-nitrobenzenesulfonic acid

A combined gas electron diffraction and quantum chemical (B3LYP/6-311+G**, B3LYP/cc-pVTZ) study of the molecular structure of 2-nitrobenzenesulfonic acid (2-NBSA) is performed. Quantum chemical calculations show that the 2-NBSA molecule has five conformers, and the Gibbs energy of one of them is lower by more than 4.5 kcal/mol than the energy of the other conformers. It is found experimentally that the saturated vapor of 2-NBSA at T = 394(5) K contains only the low-energy conformer that has an intramolecular hydrogen bond between the H atom of the hydroxyl group and one of the O atoms of the NO2 group. The C-C-S-O(H) torsion angle determining the position of the S-O(H) bond is −72(7)°, while the NO2 group is substantially turned relative to the benzene ring plane (C1-C2-N-O = 40(5)°). The following experimental values of the internuclear distances are obtained for this conformer (Å): rh1(C-H)av = 1.07(2), rh1(C-C)av = 1.401(4), rh1(C-S) = 1.767(6), rh1(S=O)av = 1.412(4), rh1(S-O) = 1.560(6), rh1(N-O)av = 1.217(5), rh1(C-N) = 1.461(8), rh1(O-H) = 0.99(3).

Structure and Energy Studies of β-Diketonates. X. Molecular Structure of Sc(aa)3 According to Gas-Phase Electron Diffraction Data

Synchronous electron diffraction and mass spectrometric investigation of the saturated vapor of scandium tris-acetylacetonate was carried out. It was stated that at 155(5)°C the vapor contains only monomeric Sc(aa)3 molecules, whose structural parameters ra, rg, and rα were determined. The internuclear distances in the chelate ring were found to be rα(Sc–O) = 2.076(4) Å, rα(O–C) = 1.271(3) Å, rα(C–Cr) = 1.386(4) Å. The coordination polyhedron ScO6 has a nearly antiprism structure of D3 symmetry. The angle of rotation of the O–O–O trigonal faces relative to their position in a regular prism is 26.8(1.1)°.

Molecular structure and vibrational characteristics of thorium tetrafluoride

The molecular structure of ThF4 is studied by synchrotron electron diffractometry and mass spectrometry. The thermally mean values of internuclear distances are found at a temperature of 1370±20 K: rg(Th-F) = 2.124(5) å, rg(F-F) = 3.418(31) å, δ(F-F) = 0.049(32) å, and LF-Th-F = 107.2(1.7)‡. These distances agree with the tetrahedral structure of the molecule. The missing vibration frequencies of the ThF4 molecule are calculated in a combined analysis of electron diffraction and spectroscopic data: v1 = 620(30) cm-1 and v2 = 115(15) cm-1.

A theoretical study of keto-enol isomerism and internal rotation in the H2Salen molecule, N,N′-ethylene-bis(salicylidenimine) — schiff base

Geometric parameters, vibrational spectra, and the energies of isomerization of seven keto-enol isomeric forms of the H2Salen molecule (N,N′-ethylene-bis(salicylidenimine)) are calculated using electron density functional theory (DFT/B3LYP) and correlation consistent valence triple-zeta Gaussian basis sets (cc-pvtz). The isomer with two enol groups (EE1) and C2 symmetry configuration is most energetically favorable. Calculations of the keto-enol equilibrium show that at T ≥ 250 K the H2Salen gas phase is a mixture of four conformers (rotamers of the main isomer EE1). The contribution of other isomers does not exceed a few percent. The NBO analysis reveals that the system of π-conjugated bonds involves not only the atoms of the benzene moiety, but also the O, C, and N atoms nearest to the benzene ring. The energy stabilization of the isomer EE1 is shown to be due to the presence of two strong intramolecular N...H hydrogen bonds. Intramolecular N...H and O...H hydrogen bonds are observed in all other isomers. The bathochromic shift of O-H and N-H vibrational frequencies, caused by the effect of hydrogen bonds, is 520–790 cm−1.

A QUANTUM CHEMICAL STUDY OF THE STRUCTURE AND ENERGY OF β-DIKETONATES. XVII. INTERNAL ROTATION OF RADICAL SUBSTITUENTS IN β-DIKETONATE MOLECULES

A quantum chemical study of the internal rotation of CX3 (X = H, F, CH3) radical substituents in scandium and calcium β-diketonate complexes is performed. Calculations are carried out using the GAUSSIAN-03 program at the HF and DFT/B3LYP levels with relativistic effective core pseudo-potentials and valence double zeta basis sets. Analytical expressions V(φ) are obtained that describe the potential energy variation during the rotation of CX3 groups. The rotation of CH3 and CF3 groups is shown to be described by a simple potential of the form V = V0/2 + V3cos(3φ), while for the description of the rotation of tert-butyl groups it is required to use a more complex function V = V0/2 + V3cos(3φ) + V6cos(6φ). Based on the obtained expressions for V(φ), the effective torsion angles φef of the rotation of CX3 groups are calculated for different temperatures. It is shown that φef obtained based on the quantum chemical calculations are close to the values obtained in electron diffraction experiments.

Molecular structure of lutetium trichloride monomer and dimer

This paper reports on a simultaneous electron diffraction and mass spectrometric study of the saturated vapor of lutetium trichloride at T = 1070(10) K. It is found that the vapor consists of the monomer LuCl3 [91.6(1.2) mol. %] and dimer Lu2Cl6. The following parameters were obtained for LuCl3 (rg configuration): rg(Lu-Cl) = 2.403(5) Å, rg(CL.Cl) = 4.119(18) Å,g(Cl-Lu-Cl) = 117.9(1.3)ℴ. Calculation of vibrational corrections for a transition from rg to rα geometry gave a planar equilibrium configuration for LuCl3 with D3h symmetry, whereas our previous electron diffraction study recommended a pyramidal configuration. Possible reasons for this controversy are discussed. The geometry of the Lu2Cl6 molecule of D2h symmetry is described by the following parameters (ra configuration): rα(Lu-Clt) = 2.366(5) Å, rα(Lu-Clα) = 2.589(24) Å, ZClt-rLu-Clt = 119(7)ℴ, ZClb-Lu-Clb = 84(2)ℴ. The mean energies of the terminal [E(Lu-Clt) = 485 kJ/mole] and bridging [E(Lu-Clb) = 292 kJ/mole] bonds of Lu2Cl26 are estimated.