Natalya V. Belova

A study of saturated vapor over the pyridine N-oxide-boron trifluoride (PyO-BF₃) adduct was carried out at T = 448(5) K by a synchronous gas electron diffraction/mass spectrometry (GED/MS) experiment. Due to the absence of ions in the mass spectrum, indicating the presence of a structure with an O-B dative bond, several models of vapor composition were tested by the GED method. It was found that the dominant molecular form (up to 100%) in vapor is the PyO-BF₃ adduct. Using the DFT/M06-2X/aug-cc-pVTZ method, geometric optimization of the molecular ion [PyO-BF₃]⁺ was carried out, which showed its intrinsic instability and dissociation into a [PyO]⁺ cation and a BF₃ molecule. This study certainly demonstrates the significant advantage of the GED method to determine the qualitative and quantitative gas-phase composition of dative-bonded adducts and other noncovalent complexes as well, whereas the interpretation of mass spectra may be ambiguous due to the possible intrinsic instability of ions containing a dative bond. The nature of the O-B bond is discussed in terms of the natural bond orbitals (NBOs) and the quantum theory of atoms in molecules (QTAIM). A comparison of structural and energetic parameters for PyO-BF₃ and the previously studied BF₃ adducts allows the theoretical comprehension of the nature of the O-B bond to be extended and to explain the different thermal stabilities of these compounds.

The enthalpies of sublimation of five substituted pyridine N-oxides were determined by the Knudsen effusion method with mass spectrometric control of the vapor composition within the framework of the second law of thermodynamics. The sublimation enthalpy of mono-substituted compounds 4-X-PyO depends on the nature of the substituent X and increases in the order CH₃→NO₂→OCH₃. A difference is noted in the nature of dissociative ionization of disubstituted derivatives 2-CH₃-4-NO₂PyO and 3-CH₃-4-NO₂PyO. The relationship between the packing of molecules in crystals and the ΔH°_subl values is considered.

The molecular structures of potassium tetrakis(hexafluoroacetylacetonato)lanthanide(III) complexes [KLn(hfa)₄] (Ln=La, Gd, Lu; hfa=C₅HF₆O₂,) were studied by synchronous gas‐phase electron diffraction/mass spectrometry (GED/MS) supported by quantum‐chemical (DFT/PBE0) calculations. The compounds sublime congruently and the vapors contain a single molecular species: the heterobinuclear complex [KLn(hfa)₄]. All molecules are ofC₁symmetry with the lanthanide atom in the center of an LnO₈coordination polyhedron, while the potassium atom is coordinated by three ligands with formation of three K−O and three K−F bonds. One hfa ligand is not bonded to the potassium atom. Topological analysis of the electron‐density distributions confirmed the existence of ionic‐type K−O and K−F bonding. The structures of the free [KLn(hfa)₄] molecules are compared with those of the related compounds [KDy(hfa)₄] and [KEr(hfa)₄] in their crystalline state. The complex nature of the chemical bonding is discussed on the basis of electron‐density topology analyses.

The Gibbs energies of solvation of 2,2'-dipyridyl (2,2'-Dipy) in methanol (MeOH), acetonitrile (AN), dimethylsulfoxide (DMSO), and N, N-dimethylformamide (DMF) are calculated via quantum...

The enthalpies of solvation of piperidine (Ppd) in methanol (MeOH), ethanol (EtOH), N, N‑dimethylformamide (DMF), and dimethylsulfoxide (DMSO) are calculated by means of quantum-chemical...

A quantum chemical study of the structure of different molecular configurations of 18-crown-6 ether (18C6) in the free state, as well as in methanol, ethanol, dimethylsulfoxide,...