Journal of Structural Chemistry最新文献

Magnesium bis-(dipivaloylmethanato)(N,N,N′,N′-tetramethylethylenediamine) [Mg(tmeda)(thd)₂] is one of the most demanded volatile fluorine-free precursors to deposit MgO films. By means of single crystal and powder X-ray diffraction we have found for the first time that during recrystallization and vacuum sublimation different polymorphs of this complex are formed: space groups P2₁/n I (previously unknown) and C2/c II (new) respectively. The new modification is also stable upon storage but does not exhibit a low-temperature phase transition with crystal splitting and symmetry lowering to (Pbar{1}) III due to the ordering of tert-butyl groups. The thermal behavior of the new polymorph is analyzed by DSC and tensimetry (flow method), which enabled us to determine the thermodynamic parameters of transformations in the condensed phase and sublimation processes. It is determined that although molecules of the complex are packed closer in the P2₁/n crystals, it does not substantially affect the vapor pressure and thermal properties at temperatures used in deposition processes. By the density functional theory with periodic boundary conditions (Quantum Espresso 7.4, PBEsol-D3(BJ)/SSSP Precision) it is shown that differences in the crystal lattice energies of three polymorphs I–III studied do not exceed 2.4 kJ/mol.

A new [Zn(tr₂ad)₂(NO₃)₂]_n (I) (tr₂ad = 1,3-bis(1,2,4-triazole-1-yl)adamantane) metal-organic framework (MOF) is prepared by solvothermal synthesis. According to the XRD data, this MOF is formed by spiral chains, left- and right-handed ones present in equal amounts in the structure. Compound I is studied by powder XRD, elemental analysis, and thermogravimetry. Its photoluminescent properties are considered. It is shown that I exhibits emission with a maximum at 448 nm and a luminescence quantum yield of 7%.

A series of 2α, 2β, 3, 4β polymorphs of 2-, 3-, 4-aminophenylbenzothiazoles (2-pbt, 3-pbt, 4-pbt) is studied by XRD. The polymorphs crystallize in polar space groups. Static orientational disorder in their crystal structures is described. The disorder is a consequence of two factors: 1) presence of pseudosymmetry D_2h in the molecules; 2) absence of strong specific intermolecular interactions. The type of symmetry transformation relating disordered positions and the disorder degree are specific to each polymorph. The highest and lowest minor position occupancies are exhibited by 2α (30%) and 2β (2%), respectively. In the case of 2-pbt polymorphs, the assumption of dynamic or static disorder caused by the intramolecular transfer of the amino group′s H atom to the heterocyclic fragment′s N atom is rejected.

Formation of Ln³⁺ lanthanide complexes with di-(2-ethylhexyl) phosphoric acid (HDEHP) is studied by the density functional theory method. In the calculations, HDEHP is modeled by dimethylphosphoric acid (HDMP). It is shown that formation of the Ln(HDMP)₃(DMP)₃ complex from the Ln(DMP)₃ complex in an organic medium is determined by two factors: lanthanide contraction and solvent polarity. The probability of Ln(HDMP)₃(DMP)₃ formation decreases with increasing lanthanide serial number and increases with decreasing solvent polarity. The presence of complexes with a number of HDMP/DMP‾ ligands larger than six in the organic medium is unlikely.

The crystal structure of 3,4-difluorobenzyloxyme and 2,4,6-trimethylbenzyloxyme is studied by X-ray diffraction. It is established that 3,4-difluorobenzyloxyme molecules form chains due to O–H⋯N hydrogen bonds, which also form dimers in the crystal packing of 2,4,6-trimethylbenzyloxyme. The crystal lattice energies are calculated by the method of pairwise interactions (DLPNO-CCSD(T)/cc-pVTZ, B3LYP-D4/6-31G(d,p) and PWPB95/def2-TZVP) and the electron density topological analysis (Espinosa–Molins–Lecomte correlation, EML). The nature and energy of intermolecular interactions are analyzed by these methods, and it is shown that the EML correlation significantly overestimates the contribution of O–H⋯N hydrogen bonds and fluorine-mediated interactions to the total energy of the molecule′s interactions and underestimates the contribution of weak C–H⋯O(N) hydrogen bonds and H⋯H interactions.

The [Pt(NH₃)₄]₃[Ta(C₂O₄)₄]₂·2H₂O (I) and [Rh(NH₃)₆][TaO(C₂O₄)₃]·2.5H₂O (II) double complex salts (DCSs) are prepared and characterized by single crystal XRD, powder XRD, and IR spectroscopy methods. Crystal data for I: P2₁/c space group, a = 7.4894(3) Å, b = 17.4414(5) Å, c = 15.4949(5) Å, β = 92.958(10)°, Z = 2. Crystal data for II: (Pbar{1}) space group, a = 7.8194(2) Å, b = 15.5143(5) Å, c = 15.8494(5) Å, α = 90.991(10)°, β = 92.096(10)°, γ = 101.549(10)°, Z = 2. Oxalic acid tantalum(V) solutions are studied by mass spectrometry; a number of complex forms in such solutions are established. Thermal decomposition processes of I and II in inert and reducing atmospheres are considered.

The interaction of 14-bromousnic acid with hydrazine dithiocarbamate is investigated. The reaction is found to proceed in two parallel paths: with modifying the bromoacetyl group into the 1,3,4-thiadiazine ring and the triketone fragment of the C ring into the pyrazole ring annelated to positions 1,2 or to 2,3 of the dibenzofuran core. Conditions are determined for the selective formation of one of the regioisomers in the structure of which the pyrazole ring is annelated to positions 1,2. It is revealed that this compound inhibits the activity of human DNA repair enzyme tyrosyl–DNA–phosphodiesterase 1 (TDP1) with a half-maximal inhibitory concentration of 1.25 µM, which enables its consideration as the basis for the synthesis of effective inhibitors of this enzyme - components of the antitumor drug.

The possibility is studied to obtain middle-entropy perovskite PbSc_1/4In_1/4Nb_1/4Ta_1/4O₃ by the sol-gel method from citric acid solutions containing F^– ions. According to synchrotron X-ray diffraction data, the synthesis passes through a low-temperature stage of forming a phase with the pyrochlore structure (500-600 °C). As the temperature increases (800 °C), this phase transforms into a phase with the perovskite structure. The composition of the synthesis product appreciably deviates from the set one and corresponds to formula Pb_1–0.9Sc_0.431±0.016In_0.142±0.014Nb_0.228±0.013Ta_0.199±0.005O_3–δF_δ. Indium, niobium, and tantalum concentrations are underestimated in it with regard to the volatility of their fluorides removed from the system at early stages of the xerogel formation during evaporation of the solution. The fluorine concentation decreases in the samples with increasing temperature due to high-temperature vapor phase hydrolysis. There is the optimal fluorine concentration (~0.04 at. % per PSINT mol) reached at 800 °C and stabilizing the perovskite structure. When the F^– concentration decreases up to zero after annealing at 1100 °C, perovskite almost completely transforms into pyrochlore.

A series of copper and zinc pentafluorobenzoate (pfb) and trifluoroacetate compounds with phosphorus-containing pyrrolidine derivatives are synthesized: [Cu(L₁–F)₂(CF₃COO)₂] (1, L₁–F - (3-(3-fluorobenzylidene)pyrrolidin-2-yl-)di(p-hexyl)phosphinoxide), [Cu(L₂–Cl)₂(CF₃COO)₂] (2, L₂–Cl - (3-(4-chlorobenzylidene)pyrrolidin-2-yl-)di(p-hexyl)phosphinoxide), [Cu(L₂–Br)₂(CF₃COO)₂] (3, L₂–Br - (3-(4-bromobenzylidene)pyrrolidin-2-yl-)di(p-hexyl)phosphinoxide), [Zn₂(L₂–Cl)₂(CF₃COO)₄] (4), [Zn₂(L₃–Et)₂(C₆F₅COO)₄] (5, L₃–Et - (1-(ethylsulfonide)pyrrolidin-2-yl)diphenylphosphinoxide), [Cu₂(L₃–Et)₂(C₆F₅COO)₄]·2MeCN (6), [Cu₂(L₃–Vi)₂(C₆F₅COO)₄] (7, L₃–Vi - (1-(vinylsulfonyl)pyrrolidin-2-yl)diphenylphosphinoxide). The coordination compounds obtained are characterized by single crystal X-ray diffraction, IR spectroscopy, and the CHNS analysis. The structures and crystal packings of the obtained complexes are studied in detail and the main structure-forming non-covalent interactions are revealed in the crystals.