Is There an Adduct of Pyridine -Oxide and Boron Trifluoride in the Gaseous State? Gas Electron Diffraction vs Mass Spectrometry.

A study of saturated vapor over the pyridine -oxide-boron trifluoride (PyO-BF) adduct was carried out at = 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-BF adduct.

First Examples of -Metal Complexes with Subporphyrazine and Its Phenylene-Annulated Derivatives: DFT Calculations.

Using quantum chemical calculation data obtained by the DFT method with the B3PW91/TZVP and M062X/def2TZVP theory levels, the possibility of the existence of four Be(II) coordination compounds, each of which contains in the inner coordination sphere and the double deprotonated forms of subporphyrazine (H), mono[benzo]subporphyrazine (H), di[benzo]subporphyrazine (H), and tri[benzo]subporphyrazine (subphthalocyanine) (H) with a ratio Be(II) ion/ligand = 1:1, were examined Selected geometric parameters of the molecular structures of these (666)macrotricyclic complexes with closed contours are given; it was noted that BeN3 chelate nodes have a trigonal-pyramidal structure and exhibit a very significant (almost 30°) deviation from coplanarity; however, all three 6-membered metal-chelate and three 5-membered non-chelate rings in each of these compounds are practically planar and deviate from coplanarity by no more than 2.5°. The bond angles between two nitrogen atoms and a Be atom are equal to 60° (in the [Be] and [Be]) or less by no more than 0.

The Perfluoro-o-phenylene-mercury Trimer [Hg(o-CF)] - a Textbook Example of Phase-Dependent Structural Differences.

The geometric and electronic structure of [Hg(o-CF)] (1) in the gas phase, i. e. free of intermolecular interactions, was determined by a synchronous gas-phase electron diffraction/mass spectrometry experiment (GED/MS), complemented by quantum chemical calculations.

Molecular Structure of Gaseous Oxopivalate Co(II): Electronic States of Various Multiplicities.

Synchronous electron diffraction/mass spectrometry was used to study the composition and structure of molecular forms existing in a saturated vapor of cobalt(II) oxopivalate at T = 410 K. It was found that monomeric complexes CoO(piv) dominate in the vapor. The complex geometry possesses the C symmetry with bond lengths Co-O = 1.

Dimer Rhenium Tetrafluoride with a Triple Bond Re-Re: Structure, Bond Strength.

Based on the data of the gas electron diffraction/mass spectrometry (GED/MS) experiment, the composition of the vapor over rhenium tetrafluoride at T = 471 K was established, and it was found that species of the ReF is present in the gas phase. The geometric structure of the ReF molecule corresponding to D symmetry was found, and the following geometric parameters of the r configuration were determined: r(Re-Re) = 2.264(5) Å, r(Re-F) = 1.

Accurate single crystal and gas-phase molecular structures of acenaphthene: a starting point in the search for the longest C-C bond.

The molecular structure of acenaphthene has been determined experimentally in the gas phase using gas electron diffraction intensities and literature-available rotational constants. Supplementary high-level quantum-chemical calculations were utilized in refinements of the semi-empirical equilibrium structure. In this work we investigate on how different schemes of GED data averaging and weighting can be used for obtaining the most accurate and precise structural parameters.

Cyclic Dimers of 4-n-Propyloxybenzoic Acid with Hydrogen Bonds in the Gaseous State.

A comprehensive study of saturated vapors of 4-n-propyloxybenzoic acid (POBA) by gas electron diffraction (GED) and mass spectrometric (MS) methods supplemented by quantum chemical (QC) calculations was carried out for the first time. An attempt was made to detect dimeric forms of the acid in the gaseous state. It has been established that at the temperature of GED experiment, vapor over a solid sample contains up to 20 mol.

Gas-phase equilibrium molecular structures and thermochemistry of anthracene and rubrene.

Semi-experimental gas-phase structures of anthracene and rubrene (5,6,11,12-tetraphenyltetracene) were determined by means of gas electron diffraction (GED). The use of the flexible restraints in the refinement of the GED data successfully resolves non-equivalent C-C bond lengths. The tetracene core of an isolated rubrene molecule was found to exhibit a twist distortion of about 18°; this is less than DFT calculations predict (30-40°).

Molecular Structure, Vibrational Spectrum and Conformational Properties of 4-(4-Tritylphenoxy)phthalonitrile-Precursor for Synthesis of Phthalocyanines with Bulky Substituent.

By DFT method with B3LYP, PBE, CAM-B3LYP, and B97D functionals, it was found that the molecule 4-(4-tritylphenoxy)phthalonitrile (TPPN) has four conformers. The geometric structure, vibrational frequencies, electronic characteristics, and thermodynamic functions of conformers, as well as the structure and energy of transition states, were determined. IR spectrum of TPPN film contains vibrational bands belonging to different conformers.

Molecular Structure of Nickel Octamethylporphyrin-Rare Experimental Evidence of a Ruffling Effect in Gas Phase.

The structure of a free nickel (II) octamethylporphyrin (NiOMP) molecule was determined for the first time through a combined gas-phase electron diffraction (GED) and mass spectrometry (MS) experiment, as well as through quantum chemical (QC) calculations. Density functional theory (DFT) calculations do not provide an unambiguous answer about the planarity or non-planar distortion of the NiOMP skeleton. The GED refinement in such cases is non-trivial.

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

Structural factors have been identified that determine the gas-phase acidity of -substituted benzenesulfonic acid, 2-XCH-SOH, (X = -SOH, -COOH, -NO, -SOF, -C≡N, -NH, -CH, -OCH, -N(CH), -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.

Accurate equilibrium structure of 3-aminophthalimide from gas electron diffraction and coupled-cluster computations and diverse structural effects due to electron density transfer.

For the first time, the molecular structure of 3-aminophthalimide has been determined by the gas electron diffraction (GED) method supported by a mass-spectrometric analysis of the gas phase and results of quantum-chemical computations up to coupled-cluster level of theory, CCSD(T). The semiexperimental equilibrium structure, rsee, has been derived from the GED data by taking into account harmonic and anharmonic vibrational corrections estimated from the quantum-chemical force field (up to cubic terms). High accuracy structures have been exploited for the observation of fine structural effects arising due the presence of the electron-donating amino group and the formation of a hydrogen bond.

Gas-Phase Structures of Potassium Tetrakis(hexafluoro- acetylacetonato) Lanthanide(III) Complexes [KLn(C HF O ) ] (Ln=La, Gd, Lu).

The molecular structures of potassium tetrakis(hexafluoroacetylacetonato)lanthanide(III) complexes [KLn(hfa) ] (Ln=La, Gd, Lu; hfa=C HF O ,) 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) ]. All molecules are of C symmetry with the lanthanide atom in the center of an LnO coordination polyhedron, while the potassium atom is coordinated by three ligands with formation of three K-O and three K-F bonds.

Molecular Structure of Pyrazinamide: A Critical Assessment of Modern Gas Electron Diffraction Data from Three Laboratories.

Accuracy and precision of molecular parameters determined by modern gas electron diffraction have been investigated. Diffraction patterns of gaseous pyrazinamide have been measured independently in three laboratories, in Bielefeld (Germany), Ivanovo (Russia), and Moscow (Russia). All data sets have been analyzed in equal manner using a highly controlled background elimination procedure and flexible restraints in molecular structure refinement.

Molecular structure and electron distribution of 4-nitropyridine N-oxide: Experimental and theoretical study of substituent effects.

The molecular structure of 4-nitropyridine N-oxide, 4-NO-PyO, has been determined by gas-phase electron diffraction monitored by mass spectrometry (GED/MS) and by quantum chemical calculations (DFT and MP2). Comparison of these results with those for non-substituted pyridine N-oxide and 4-methylpyridine N-oxide CH-PyO, demonstrate strong substitution effects on structural parameters and electron density distribution. The presence of the electron-withdrawing -NO group in -position of 4-NO-PyO results in an increase of the ipso-angle and a decrease of the semipolar bond length (N→O) in comparison to the non-substituted PyO.

Ligand Coordination in Bis(β-diketonato) d Metals: The Mn(II) Case of D versus D Symmetry.

The structure of free manganese(II) bis-acetylacetonate [Mn(acac)] was determined experimentally by gas-phase electron diffraction. The vapor at 197(5) °C is composed of a single conformer of Mn(acac) in D symmetry with a central structural motif of an elongated MnO tetrahedron with a Mn-O distance ( r) of 2.035(5) Å and a bond angle in chelate rings (∠O-Mn-O) of 89.

The molecular structure of 4-methylpyridine-N-oxide: Gas-phase electron diffraction and quantum chemical calculations.

The molecular structure of 4-methylpiridine-N-oxide, 4-MePyO, has been studied by gas-phase electron diffraction monitored by mass spectrometry (GED/MS) and quantum chemical (DFT) calculations. Both, quantum chemistry and GED analyses resulted in molecular symmetry with the planar pyridine ring. Obtained molecular parameters confirm the hyperconjugation in the pyridine ring and the sp hybridization concept of the nitrogen and carbon atoms in the ring.

The Structure of Mn(acac) -Experimental Evidence of a Static Jahn-Teller Effect in the Gas Phase.

The structure of free manganese(III) tris(acetylacetonate) [Mn(acac) ] was determined by mass-spectrometrically controlled gas-phase electron diffraction. The vapor of Mn(acac) at 125(5) °C is composed of a single conformer of Mn(acac) in C symmetry with the central structural motif of a tetragonal elongated MnO octahedron and 47(2) mol % of acetylacetone (Hacac) formed by partial thermal decomposition of Mn(acac) . Three types of Mn-O separations have been refined (r =2.

Gas-phase structure of 1,8-bis[(trimethylsilyl)ethynyl]anthracene: cog-wheel-type vs. independent internal rotation and influence of dispersion interactions.

The gas-phase structure of 1,8-bis[(trimethylsilyl)ethynyl]anthracene (1,8-BTMSA) was determined by a combined gas electron diffraction (GED)/mass spectrometry (MS) experiment as well as by quantum-chemical calculations (QC). DFT and dispersion corrected DFT calculations (DFT-D3) predicted two slightly different structures for 1,8-BTMSA concerning the mutual orientation of the two -C-C[triple bond, length as m-dash]C-SiMe units: away from one another or both bent to the same side. An attempt was made to distinguish these structures by GED structural analysis.

Accurate Determination of Equilibrium Structure of 3-Aminophthalonitrile by Gas Electron Diffraction and Coupled-Cluster Computations: Structural Effects Due to Intramolecular Charge Transfer.

For the first time, the molecular structure of 3-aminophthalonitrile with unique electronic properties has been determined by the gas electron diffraction (GED) method supported by a mass spectrometric analysis of the gas phase. Moreover, it has been optimized at the high-level quantum-chemical coupled-cluster theory, CCSD(T), in conjunction with the triple-ζ basis set. The equilibrium structure has been determined from the GED data taking into account harmonic and anharmonic vibrational corrections estimated from the quantum-chemical force field (up to cubic terms).

1,8-Bis(phenylethynyl)anthracene - gas and solid phase structures.

1,8-Bis(phenylethynyl)anthracene (1,8-BPEA) was synthesized by a twofold Kumada cross-coupling reaction. The molecular structure of 1,8-BPEA was determined using a combination of gas-phase electron diffraction (GED), mass spectrometry (MS), quantum chemical calculations (QC) and single-crystal X-ray diffraction (XRD). Five rotamers of the molecule with different orientations of phenylethynyl groups were investigated by DFT calculations.

Structures and intriguing conformational behavior of 1- and 2-naphthalenesulfonamides as determined by gas-phase electron diffraction and computational methods.

The saturated vapors of 1- and 2-naphthalenesulfonamides (1-NaphSA and 2-NaphSA) were studied by the gas-phase electron diffraction/mass-spectrometric method at 413(9) and 431(9) K. According to quantum chemical calculations (DFT/B3LYP and MP2 with cc-pVDZ, aug-cc-pVDZ, cc-pVTZ, and aug-cc-pVTZ basis set) 1-NaphSA possesses four conformers with different orientations of the SO2NH2 fragment relative to the naphthalene frame and eclipsed or staggered orientation of the N-H and S═O bonds, whereas 2-NaphSA possesses only two conformers with different orientations of the N-H and S═O bonds. It was experimentally established that vapors over 1-NaphSA and 2-NaphSA exist predominantly (up to 75 mol %) of low-energy conformers of C1 symmetry in which the C-S-N planes deviate from perpendicular orientation relative to the naphthalene skeleton with near eclipsed orientation of the N-H and S═O bonds of the SO2NH2 fragment.

Tautomeric properties and gas-phase structure of acetylacetone.

The tautomeric and structural properties of acetylacetone, CH3C(O)CH2C(O)CH3, have been studied by gas-phase electron diffraction (GED) and quantum chemical calculations (B3LYP and MP2 approximation with different basis sets up to aug-cc-pVTZ). The analysis of GED intensities resulted in the presence of 100(3)% of the enol tautomer at 300(5) K and 64(5)% of the enol at 671(7) K. The enol tautomer possesses Cs symmetry with a planar ring and strongly asymmetric hydrogen bond.

The re-determination of the molecular structure of antimony(III) oxide using very-high-temperature gas electron diffraction (VHT-GED).

The molecular structure of a fundamental binary compound [antimony(III) oxide] has been re-determined to a far higher accuracy and precision than previously reported. The structure is compared to those determined by various ab initio methods, X-ray diffraction and to a previous gas-phase structure determined by electron diffraction prior to modern-day developments for data extraction and manipulation. The experiments utilised a new very-high-temperature (VHT) inlet nozzle system that has been designed and constructed for the gas electron diffraction (GED) apparatus now based at the University of Canterbury (formerly at the University of Edinburgh).

Molecular structure and bonding in octamethylporphyrin tin(II), SnN4C28H28.

Gas-phase electron diffraction was applied for the molecular structure determination of octamethylporphyrin tin(II), SnN(4)C(28)H(28), at the temperature of 706(10) K. The molecule was found to possess C(4v) symmetry with the Sn atom 1.025(30) Å above the plane of the N atoms and the following main internuclear distances (r(h1), Å): Sn-N = 2.