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 Co4O(piv)6 dominate in the vapor. The complex geometry possesses the C3 symmetry with bond lengths Co-Oc = 1.975(5) Å and Co-O = 1.963(5) Å, as well as bond angles Oc-Co-O = 111.8(3)°, Co-Oc-Co = 110.4(6)°, O-Co-O = 107.1(3)° in the central OcCo4 fragment and four OcCoO3 fragments. The presence of an open 3d shell for each Co atom leads to the possibility of the existence of electronic states of the Co4O(piv)6 complex with Multiplicities 1, 3, 5, 7, 9, 11, and 13. For them, the CASSCF and XMCQDPT2 calculations predict similar energies, identical shapes of active orbitals, and geometric parameters, the difference between which is comparable with the error of determination by the electron diffraction experiment. QTAIM and NBO analysis show that the Co-Oc and Co-O bonds can be attributed to ionic (or coordination) bonds with a significant contribution of the covalent component. The high volatility and simple vapor composition make it possible to recommend cobalt (II) oxopivalate as precursors in the preparation of oxide films or coatings in the CVD technologies. The features of the electronic and geometric structure of the Co4O(piv)6 complex allows for the conclude that only a very small change in energy is required for the transition from antiferromagnetically to ferromagnetically coupled Co atoms.

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 Re2F8 is present in the gas phase. The geometric structure of the Re2F8 molecule corresponding to D4h symmetry was found, and the following geometric parameters of the rh1 configuration were determined: rh1(Re-Re) = 2.264(5) Å, rh1(Re-F) = 1.846(4) Å, α(Re-Re-F) = 99.7(0.2)°, φ(F-Re-Re-F) = 2.4 (3.6)°. Calculations by the self-consistent field in full active space approximation showed that for Re2F8, the wave function of the 1A1g ground electronic state can be described by the single closed-shell determinant. For that reason, the DFT method was used for a structural study of Re2X8 molecules. The description of the nature of the Re-Re bond was performed in the framework of Atom in Molecules and Natural Bond Orbital analysis. The difference in the experimental values of r(Re-Re) in the free Re2F8 molecule and the [Re2F8]2- dianion in the crystal corresponds to the concept of a triple σ2π4 (ReIV-ReIV) bond and a quadruple σ2π4δ2 (ReIII-ReIII) bond, respectively, which are formed between rhenium atoms due to the interaction of d-atomic orbitals. The enthalpy of dissociation of the Re2F8 molecular form in two monomers ReF4 (ΔdissH°(298) = 109.9 kcal/mol) and the bond energies E(Re-Re) and E(Re-X) in the series Re2F8→Re2Cl8→Re2Br8 molecules were estimated. It is shown that the Re-Re bond energy weakly depends on the nature of the halogen, while the symmetry of the Re2Br8 (D4d) geometric configuration differs from the symmetry of the Re2F8 and Re2Cl8 (D4h) molecules.

Gas-Phase Structure of 3,7,9-tris(trifluoromethylsulfonyl)-3,7,9-triazabicyclo[3.3.1]nonane by GED and Theoretical Calculations.

The molecular structure and conformational and rotational composition of 3,7,9-tris(trifluoromethylsulfonyl)-3,7,9-triazabicyclo[3.3.1]nonane 1 have been investigated by synchronous gas-phase electron diffraction/mass spectrometry GED/MS and theoretical calculations (B3LYP and M06-2X with cc-pVTZ and aug-cc-pVTZ basis sets) and compared to the X-ray structure. All 16 possible conformers and rotamers were calculated, differing by the conformations of the two piperazine rings, orientation of the CF3 groups relative to these rings, and non-equivalence of the two wings of the butterfly structure. The optimized geometry of the most stable 1-c-out-2-c-out conformer coincides with that in the crystal. In contrast to only one conformer determined by X-ray, the GED analysis revealed the presence of five conformers, 1-c-out-2-c-out (I), 1-c-in-2-c-out (II), 1-c-out-2-c-in (III), 1-b-out-2-c-out (IV), 1-c-out-2-b-out (V) in the ratio of I:(II + III):IV:V = 36(10):42(6):22(10):0(10). The experimental results are better reproduced by calculations performed for 428 K (the temperature of the GED experiment) than for 298 K (standard), and most satisfactorily at the M06-2X/aug-cc-pVTZ level of theory.

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.% of cyclic dimers with two O-H...O hydrogen bonds. The main geometrical parameters of gaseous monomers and dimers of POBA are obtained. The distance r(O…O) = 2.574(12) Å in the cyclic fragment of the gaseous dimer is close to that in the crystal structure (2.611 Å). In the mass spectrum of the POBA recorded the ions of low intensity with a mass exceeding the molecular mass of the monomer were detected. The presence of ions, whose elemental composition corresponds to the dissociative ionization of the dimer, confirms the results of the GED experiment on the presence of POBA dimers in the gas state. The results of GED studies of acetic acid, benzoic acid, and POBA were compared. It is shown that the COOH fragment saves its geometric structure in monomers, as well as the COOH...HOOC fragment with two hydrogen bonds in dimers of different acids. The intermolecular interaction energy in considered acid dimers was estimated using QC calculations (B97D/6-311++G **). The significant value of last (>84 kJ/mol) is the reason for the noticeable presence of dimers in the gas phase.

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. The assignment of bands was performed basing the distribution of normal vibration energy on internal coordinates. A synchronous electron diffraction/mass spectrometric experiment was performed to determine the structure of conformers in a saturated TPPN vapor. The elemental composition of the ions recorded in the mass spectrum indicates the thermal stability of TPPN at least up to T = 200 °C. The difference in the structure of tetrasubstituted metal phthalocyanines, which can be synthesized from different TPPN conformers, has been shown.

Spectroscopic Properties, Conformation and Structure of Difluorothiophosphoryl Isocyanate in the Gaseous and Solid Phase.

Difluorothiophosphoryl isocyanate, F2P(S)NCO was characterized with UV/vis, NMR, IR (gas and Ar-matrix), and Raman (liquid) spectroscopy. Its molecular structure was also established by means of gas electron diffraction (GED) and single crystal X-ray diffraction (XRD) in the gas phase and solid state, respectively. The analysis of the spectroscopic data and molecular structures is complemented by extensive quantum-chemical calculations. Theoretically, the Cs symmetric syn-conformer is predicted to be the most stable conformation. Rotation about the P-N bond requires about 9 kJ mol-1 and the predicted existence of an anti-conformer is dependent on the quantum-chemical method used. This syn-orientation of the isocyanate group is the only one found in the gas phase and contained likewise in the crystal. The overall molecular structure is very similar in gas and solid, despite in the solid state the molecules arrange through intramolecular O⋅⋅⋅F contacts into layers, which are further interconnected by S⋅⋅⋅N, S⋅⋅⋅C and C⋅⋅⋅F contacts. Additionally, the photodecomposition of F2P(S)NCO to form CO, F2P(S)N, and F2PNCO is observed in the solid Ar-matrix.

Inter- and Intramolecular Aryl-Aryl Interactions in Partially Fluorinated Ethylenedioxy-bridged Bisarenes*.

Several ethylenedioxy-bridged bisarenes with a variety of type and number of aryl groups were synthesized to study non-covalent dispersion-driven inter- and intramolecular aryl-aryl interactions in the solid state and gas phase. Intramolecular interactions are preferably found in the gas phase. DFT calculations with and without dispersion correction show larger interacting aromatic groups increase the stabilization energy of folded conformers and decrease the intermolecular centroid-centroid distance. Single-molecule structures generally adopt folded conformations with short intramolecular aryl-aryl contacts. Gas electron diffraction experiments were performed exemplarily for 1-(pentafluorophenoxy)-2-(phenoxy)ethane. A new procedure for structure refinement was developed to deal with the conformational complexity of such molecules. The results are an experimental confirmation of the existence of folded conformations of this molecule with short intramolecular aryl-aryl distances in the gas phase. Solid-state structures are dominated by stretched structures without intramolecular aryl-aryl interactions but interactions with neighboring molecules.

Solid-State and Gas-Phase Structures and Energetic Properties of the Dangerous Methyl and Fluoromethyl Nitrates.

An improved synthesis of the simplest nitric acid ester, methyl nitrate, and a new synthesis of fluoromethyl nitrate use the metathesis of the corresponding iodomethanes with silver nitrate. Both compounds were identified by spectroscopy and the structures determined for in situ grown crystals by X-ray diffraction as well as in the gas phase by electron diffraction. Fluorination leads to structures with shorter C-O and N-O bonds, has an energetically destabilizing effect and increases friction sensitivity, but decreases detonation performance.

Intramolecular π-π Interactions in Flexibly Linked Partially Fluorinated Bisarenes in the Gas Phase.

Three compounds with phenyl and pentafluorophenyl rings bridged by (CH2 )3 and (CH2 )2 SiMe2 units were synthesized by hydrosilylation and C-C coupling reactions. Their solid-state structures are dominated by intermolecular π stacking interactions, primarily leading to dimeric or chain-type aggregates. Analysis of free molecules in the gas phase by electron diffraction revealed the most abundant conformer to be significantly stabilized by intramolecular π-π interactions. For the silicon compounds, structures characterized by σ-π interactions between methyl and pentafluorophenyl groups are second lowest in energy and cannot be excluded completely by the gas electron diffraction experiments. C6 H5 (CH2 )3 C6 F5 , in contrast, is present as a single conformer. The gas-phase structures served as a reference for the evaluation of a series of (dispersion-corrected) quantum-chemical calculations.

Gas phase structures of peroxides: experiments and computational problems.

Gas-phase structures of several organic and inorganic peroxides X-O-O-X and X-O-O-X', which have been determined experimentally by gas electron diffraction and/or microwave spectroscopy, are discussed. The OO bond length in these peroxides varies from 1.481(8) Å in Me3 SiOOSiMe3 to 1.214(2) Å in FOOF and the dihedral angle ϕ(XO-OX) between 0° in HC(O)O-OH and near 180° in Bu(t) O-OBu(t) . Some of the peroxides cause problems for quantum chemistry, since several computational methods fail to reproduce the experimental structures. Extreme examples are MeO-OMe and FO-OF. In the case of MeO-OMe only about half of the more than 100 computational methods reported in the literature reproduce the experimentally determined double-minimum shape of the torsional potential around the OO bond correctly. For FO-OF only a small number of close to 200 computational methods reproduce the OO and OF bond lengths better than ±0.02 Å.