Nina I. Giricheva

Compounds of metals with organic moieties cover the widest classes of chemical substances, with various applications in the chemical industry, catalysis, microelectronics, sensors, medicine, pharmacology, etc

Using a combination of experimental methods (polarizing optical microscopy, IR spectroscopy), the two-component systems consisting of 4-dodecyloxybenzoic acid (BA) and 4-(4-alkoxyphenylazo)benzonitriles (BN-n, n = 8, 10, 12) have been studied. The mesophase existence ranges of the systems depending on the length of alkyl substituents of the component BN-n were established. The possibility of formation as well as stability of heterodimeric complexes with a hydrogen bond –COOH···NC – were analyzed by DFT/B97D/6-311++G** method. In all obtained equimolar BN-n:BA (1:1) systems SmA phase was induced, which manifests itself enantiotropically in wide temperature ranges. With the help of computer simulation, it was shown that, unlike homodimers, the expected BN···BA H-complex has an angular structure, which cannot ensure the formation of the SmA phase. To elucidate the mechanism of mesophase formation in BN-n:BA systems, we calculated the energies of intermolecular interaction in homo- and heterodimers, and analyzed the experimental IR spectra of equimolar BN-n:BA systems. The spectra represent a superposition of the spectra of associates BN···BN and cyclic dimers of acid BA···BA. Therefore, we suggest that the BN···BA type H-complexes cannot form in equimolar BN-n:BA mixtures. Instead, a structure consisting of alternating layers of BA···BA dimers and BN···BN associates is formed. The layers of the acid dimer play the main role in the formation of SmA phase. It is noted that –COOH group, in contrast to such proton-donor groups as –NH2, –NH–, –OH, does not form hydrogen bonds with the proton-acceptor –CN group.

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–O_c = 1.975(5) Å and Co–O = 1.963(5) Å, as well as bond angles O_c–Co–O = 111.8(3)°, Co–O_c–Co = 110.4(6)°, O–Co–O = 107.1(3)° in the central O_cCo₄ fragment and four O_cCoO₃ 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–O_c 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.

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 D_4h symmetry was found, and the following geometric parameters of the r_h1 configuration were determined: r_h1(Re-Re) = 2.264(5) Å, r_h1(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 ¹A_1g 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 (Re^IV-Re^IV) bond and a quadruple σ²π⁴δ² (Re^III-Re^III) 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 (Δ_dissH°(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 (D_4d) geometric configuration differs from the symmetry of the Re₂F₈ and Re₂Cl₈ (D_4h) molecules.

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.

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.

С помощью экспериментальных и теоретических методов показано, что в двухкомпонентных системах состава 1:1 на основе 4-пиридил-4’-н-алкилоксибензоатов (n = 7, 12) с 4-(фенилазо)бензойной кислотой и 4-(фенилазо)фенолом формируются водородосвязанные молекулярные комплексы. Методами квантовой химии (DFT (B3LYP)/cc-pVTZ) определены конформационные свойства молекул 4-(фенилазо)бензойной кислоты, 4-(фенилазо)фенола. Показано, что введение в молекулу азобензола 4-карбокси- и 4-гидгрокси-групп практически не влияет на энергетические характеристики процесса транс-цис изомеризации. Выполнена оценка энергетических, геометрических и электронных характеристик межмолекулярных водородных связей в исследуемых комплексах. Результаты расчетов показали, что H-комплексы 4-пиридил-4-н-пропилоксибензоата с 4-(фенилазо)бензойной кислотой и 4-(фенилазо)фенолом значительно отличаются друг от друга по геометрическому строению: комплекс с 4-(фенилазо)бензойной кислотой – стержнеобразный, комплекс с 4-(фенилазо)фенолом – ангулярный. Сравнение энергетических характеристик H-комплексов, а также характеристик водородных связей показало, что в комплексе с участием 4-(фенилазо)бензойной кислотой формируется более прочная водородная связь, чем в комплексе с 4-(фенилазо)фенолом. Результаты моделирования димеров молекул 4-(фенилазо)бензойной кислотой, 4-(фенилазо)фенола, воспроизводящих межмолекулярные взаимодействия в кристаллах, и их H-комплексов с 4-пиридил-4’-алкилоксибензоатами позволили сделать вывод, что в процессе самоорганизации в исследуемых системах состава 1:1 будут разрушаться ассоциаты молекул 4-(фенилазо)бензойной кислоты, ассоциаты молекул 4-(фенилазо)фенола и формироваться H-комплексы с 4-пиридил-4’-алкилоксибензоатами. Изменения экспериментальных ИК спектров, зарегистрированных для исходных компонентов и для систем состава 1:1, подтверждают формирование молекулярных комплексов. Структурными единицами исследуемых систем на основе 4-пиридил-4’-н-алкилоксибензоатов с 4-(фенилазо)бензойной кислотой и 4-(фенилазо)фенолом состава 1:1 можно считать супермолекулы, образующиеся за счет водородной связи. Строение молекулярных комплексов и наличие у них геометрической анизотропии свидетельствуют об их потенциальной мезогенности. Полученный образец H-комплексов 4-(фенилазо)фенола и 4-пиридил-4’-додецилоксибензоата (состава 1:1) был исследован на предмет проявления мезоморфных свойств с помощью метода поляризационной термомикроскопии. Зарегистрированные в поляризационном микроскопе текстуры позволяют заключить, что H-комплекс обладает смектической мезофазой в температурном интервале 101,4-109,4 °С. Для цитирования: Федоров М.С., Филиппов А.А., Филиппов И.А., Гиричева Н.И., Сырбу С.А., Киселев М.Р. Водородная связь в потенциально мезогенных молекулярных комплексах 4-(фенилазо)бензойной кислоты и 4-(фенилазо)фенола с производными пиридина. Изв. вузов. Химия и хим. технология. 2022. Т. 65. Вып. 12. С. 12-23. DOI: 10.6060/ivkkt.20226512.6665.