Roman I. Zubatyuk

Homonuclear versus heteronuclear resonance-assisted hydrogen bonds: tautomerism, aromaticity, and intramolecular hydrogen bonding in heterocyclic systems with different exocyclic proton donor/acceptor.

Tautomerism and resonance-assisted hydrogen bonding have been analyzed on the basis of the results of ab initio calculations at the MP2/AUG-cc-pVDZ level of theory for the series of molecules containing different heterocycles connected with resonance spacer and containing different exocyclic proton donor/acceptor atoms. It is demonstrated that the position of tautomeric equilibrium is controlled mainly by two factors: aromaticity of heterocycle, which could be different for two tautomers, and relative proton affinities of two heteroatoms forming a hydrogen bond. Replacement of exocyclic proton donor/acceptor atom results in change of an aromaticity degree of heterocycle leading to alteration of relative stability of tautomers. Comparison of structure and properties of E and Z conformers of molecules demonstrates resonance-assisted character of intramolecular hydrogen bond. Application of the NBO theory reveals that the pi-component of the electron density within resonant spacer plays the primary role for determination of characteristics of hydrogen bond while sigma-skeleton only reflects the pi-polarization. An analysis of strength of intramolecular hydrogen bond using geometrical, energetic, and AIM and NBO parameters indicates that the homonuclear N...H-N hydrogen bond is considerably weaker than heteronuclear N...H-O and N...H-S hydrogen bonds in the case of the XH tautomers.

Direct Synthesis, Crystal Structures, High-Field EPR, and Magnetic Studies of Heterometallic Polymers Containing Manganese(II) Carboxylates Interconnected by [Cu(en)2]2+

Two heterometallic polymers containing cations [Cu(en)2]2+ and either the [Mn(mal)2(H2O)2]2- (1) or [Mn2(succ)2Cl2]n2n- (2) anions (mal=malonate and succ=succinate) were investigated by X-ray crystallography, high-field electron paramagnetic resonance (EPR) spectroscopy, and magnetic susceptibility measurements. Magnetic susceptibility and EPR spectra characteristic of antiferromagnetically coupled Mn2+-Mn2+ pairs were observed in 2, and the exchange integral J=31 cm(-1) (H=JS1S2) as well as the zero-field-splitting parameter D=-3.046 cm(-1) in the triplet state of the dimanganese entity was determined.

Exploration of density functional methods for one-electron reduction potential of nitrobenzenes.

Performance of the set of density functional approaches for calculation of one‐electron reduction potentials of nitroaromatic compounds was investigated. To select the most precise and affordable method, we selected a set of model molecules and investigated effects of basis set, density functional, and solvation model on the calculation of reduction potentials. It was found that the mPWB1K/TZVP method provides the most accurate gas phase electron affinity values (RMS error is 0.1 eV). This method in conjunction with the PCM (Bondi) method yields also the most accurate difference in solvation energies of neutral oxidized form and anion‐radical reduced form. The final E0 values were calculated with RMS error of 0.10 V, compared with experimental values.

Role of supramolecular synthons in the formation of the supramolecular architecture of molecular crystals revisited from an energetic viewpoint

Analysis of the strengths and directionality of intermolecular interactions in the crystals containing only one type of supramolecular synthon allows the suggestion of a general classification of molecular crystals depending on type of their basic structural motifs. All crystals may be divided on four classes namely (I) crystals with isotropic packing of the building units; (II) columnar crystals where the basic structural motif (BSM) is a chain/column; (III) layered crystals with layers as the BSM; (IV) columnar-layered crystals containing chains/columns as the primary basic structural motif and layers as the secondary BSM. Taking into account the participation of different supramolecular synthons in the formation of different levels of the organization of molecular crystals, they may be considered as basic (responsible for the formation of molecular complexes as building units of crystals), primary, secondary and auxiliary, which are involved in the agglomeration of molecules in primary or secondary basic structural motifs or in the packing of these motifs, respectively. The ranking of supramolecular synthons depends on values of energies of intermolecular interactions and it is individual for each crystal.

Supramolecular architecture of molecular crystals possessing shearing mechanical properties: columns versus layers

The supramolecular architectures of crystals of substituted benzenes possessing shearing mechanical properties have been analyzed from the viewpoint of energy of intermolecular interactions. It is demonstrated that suggested earlier layered structure of these crystals do not correspond to the character of intermolecular interactions. Analysis of the topology of intermolecular interactions indicates that the crystals have a columnar supramolecular architecture with weak interactions between the columns. The presence of shearing mechanical properties is caused by localization of intercolumnar interactions within some layers and a relatively small (less than 12 kcal mol−1) barrier of shift of molecules within this layer.

Low-melting molecular complexes. Halogen bonds in molecular complexes of bromoform

Single crystals of three new low-melting molecular complexes of bromoform have been grown in situ, their crystal structures characterized by X-ray crystallography and compared with those of their chloroform analogues. The calculations of pair-wise energies of intermolecular interactions in these structures reveal that in some cases the strongest interactions exist between the molecules which are not linked by any short direction-specific intermolecular contacts. A high versatility of bonding modes of bromoform in comparison to chloroform is demonstrated and the relative role of various intermolecular interactions (including halogen bonds) in studied molecular complexes is discussed.

Influence of Deuteration and Fluorination on the Supramolecular Architecture of Pyridine N‐Oxide Crystals

To understand how deuterium and fluorine substituents influence the supramolecular architecture of pyridine N-oxide crystals, the crystal structure of 3-fluoropyridine N-oxide (PNO-3F) was determined and the crystal packing motives of non-deuterated pyridine-N-oxide (PNO), partial-deuterated pyridine-N-oxide (PNO-D) and PNO-3F were analyzed based on ab initio quantum-chemical calculations of the intermolecular interaction energy, using the MP2/6-311G(d,p) method. The appearance of the weak-directing substituents deuterium and fluorine leads to significant changes in the crystal organization of the isotropic packing of PNO molecules.

Synthesis and structure of N-alkyl(aryl)aminocarbonyl-1,4-benzoquinone imines

New N-alkyl(aryl)aminocarbonyl-1,4-benzoquinone imines were synthesized by reaction of isocyanates with the corresponding substituted 4-aminophenols, and their structure was determined on the basis of 1H and 13C NMR spectra and X-ray diffraction data.

Role of different molecular fragments in formation of the supramolecular architecture of the crystal of 1,1-dioxo-tetrahydro-1λ6-thiopyran-3-one

The crystal structure of 1,1-dioxo-tetrahydro-1λ6-thiopyran-3-one has been determined and analyzed in terms of the topology of intermolecular interactions between the basic molecule located in the asymmetric part of the unit cell and its first coordination sphere. Supramolecular architecture of the crystal represents packing of strongly bonded flat layers formed mainly due to the SO⋯H–C hydrogen bonds. Comparison of the crystal structure of the title compound and its analogues demonstrates the major role of the sulfonic group in the crystal organization. A layered structure is observed also for cyclic sulfone without the carbonyl group and in the case of replacement of the CO bond by a cyclic oxygen atom. Presence of a saturated six-membered ring is a second factor influencing the crystal structure of the title compound. Absence of a ring in the dimethylsulfone results in formation of a highly corrugated columnar structure. Similar architecture of the crystal is found also for the cyclohexanone. A highly corrugated columnar structure is observed also in the case of replacement of the carbonyl group of the title compound by a considerably more polar sulfoxide S–O bond which is more active in the formation of intermolecular hydrogen bonds than a sulfone SO2 group.

INVESTIGATION OF TOPOLOGY OF INTERMOLECULAR INTERACTIONS IN THE BENZENE-ACETYLENE CO-CRYSTAL BY DIFFERENT THEORETICAL METHODS

Crystal structure of benzene–acetylene co-crystal was analysed based on calculated energies of intermolecular interactions between basic molecules located in asymmetric part of unit cell and their neighbours belonging to their first coordination sphere. It is demonstrated that the basic structural motif of the crystal is represented by infinite chains formed by the hydrogen-bonded benzene and acetylene molecules. Energy of interaction of the basic pair of molecules to neighbours within the chain is 2.2 times higher than the energy of interactions with molecules of any neighbouring chain. This ratio almost does not depend on method of calculation of interaction energy. Also, results of calculations were compared with analysis of topology of electron density distribution in crystal. The possibility to find the basic structural motif of the crystal based on properties of intermolecular bond critical points is demonstrated.