Home – Home – Jornals – Advanced Search

An X-ray study of (3Z)-(±)-4-(2′-hydroxypropyl)amino- and (3Z)-4-(2′-hydroxyethyl)aminopent-3-en-2-ones is reported. The bond lengths inside the H ring are equalized due to the classical N-H…O hydrogen bond between the carbonyl oxygen and the amino group. In the 4-(2′-hydroxyethyl)aminopent-3-en-2-one crystal, due to the classical N-H…O bonds, infinite zigzag chains are formed along the 0b axis and arranged into a layered structure due to the weak C-H…O interactions. In (±)-4-(2′-hydroxypropyl)amino-pent-3-en-2-one crystal, however, centrosymmetric dimers are formed, which are then linked by weak
C-H…O intermolecular interactions, which form a layered structure along the a0b plane.

Pseudohalogen-containing compounds have attracted significant interest among nonmetal chemists and theorists, not only owing to their potential use in various fields but also due to difficulties in their experimental preparation and characterization. Since its introduction in 1925, the pseudohalide principle has been used extensively and, therefore, a remarkable progress has been made in the experimental and theoretical research on the compounds of this kind. In this work, we review studies on structural investigations and theoretical characterizations of several pseudohalide-containing compounds in order to contribute to better understanding of the chemistry of many such species.

Non-empirical RHF/6-31G* and MP2/6-31G* quantum chemical methods are used to calculate the molecular structure of trichlorophosphazene compounds: Cl₃P=NC(CF₃)₃ (I) and Cl₃P=NCCl(CCl₃)₂ (II). The corresponding geometric parameters obtained from the calculations are compared with X-ray diffraction analysis data reported in the literature. Conformational differences between the molecules of I and II, previously found by X-ray diffraction in the crystals of these compounds, are confirmed by non-empirical calculations of the molecules in the free state. The features of their geometry caused by intramolecular interactions are discussed.

Based on graph theory fundamentals, a general formula to calculate formal unsaturation of chemical compounds that contain atoms of any valence is deduced and the mathematical meaning of this widely used chemical concept is shown.

Using the results of Monte Carlo simulation, equations of state of hard sphere liquids are calculated for 106 values of the fill factor η = 0.005-0.530 (step of 0.005). In the region of liquid phase stability the absolute accuracy of about 0.00001-0.00008 is reached. Correctness of the accuracy estimate is discussed. The results obtained are compared with reported equations of state of the hard sphere liquid.

Primary data of the X-ray diffraction experiment on DyBr₃ and YbBr₃ aqueous solutions in salt:water molar ratios of 1:20 are presented. The occurrence of a pre-main peak in the curves of normalized scattering intensities determines the average distance between cations in these solutions, and hence, directs to a model description of the structure of solutions. Based on the determination of boundaries of the cation complex and taking into account the deficit of solvent, the model of the cation complex is supposed to consist of two coordination shells involving at least two anions.

The crystal structure and the formation conditions of crystals of the LiFe₅O₈ ordered phase obtained from the solution-melt of the Bi₂O₃-Fe₂O₃-B₂O₃-LiCl quadruple system are refined. The crystals are black, octahedral, of cubic symmetry (space group P4₃32). Unit cell parameters: a = 8.3339(1) Е, V = 578.82(1) Е³, Z = 4, d_calc = 4.753 g/cm³. From 6046 of the collected array I_hkl 358 are independent (R_int = 0.0321). As a result of anisotropic refinement of structural parameters, R₁ factor is found to be 0.0186 (wR₂ = 0.0467). Lithium atoms are in octahedral environment, Li-O is 2.109(1) Е; iron atoms are of two types: in octahedra with Fe-O (by two) distances of 1.9586(9) Е, 2.0152(9) Е, and 2.0652(10) Е and tetrahedra with Fe-O (three) 1.8848(10) Е and 1.914(2) Е. The structure is of inverted spinel type.

Triclinic modification of trans-bis(trifluoroacetylacetonato)copper(II) has been studied by single crystal X-ray diffraction (diffractometer X8 APEX BRUKER, MoK_α radiation, T = 173(2) K). The structure is molecular. Square environment of the Cu atom (Сu-O_av 1.916 Е, ∠O-Сu-O_av 93.4°) is completed to a bi-pyramid by two Сγ atoms of neighboring molecules, Cu…Сγ 3.18 Е and 3.23 Е.

Crystal structure of acrylamide has been re-determined by single crystal X-ray diffraction (133(1) K, BRUKER SMART 1000 CCD, a = 8.228(1) Е, b = 5.759(1) Е, c = 9.760(1) Е, β = 120.04(1)°, V =
400.3(1) Е³, space group P2₁/c, Z = 4, R = 0.0543 for 867 reflections). In the structure strong hydrogen bonds N-H…O join the molecules of C₃H₅NO into bi-molecular layers, which make C…C molecular contacts. It has been demonstrated that the process of sold phase polymerization of acrylamide should proceed through the cleavage of double bonds С(1)=С(2) in the monomers and formation of bonds С(1)-С(1) and С(2)-С(2) between the closest carbon atoms of different layers.

Addition of trichloroacetonitrile to 2,5-dimethyl-1,5-hexadiene in presence of cuprous amine complexes has been studied. Single crystal X-ray diffraction unambiguously proves that the main product is a racemic mixture of the cyclic symmetric nitrile - (1r,3R,6S)- and (1r,3S,6R)-1,3,6-trichloro-3,6-dimethylcycloheptanecarbonitrile. Established relative configuration of the product confirms the ring closure mechanism suggested before. Also, a side product - 2,5-dimethyl-2,5-dichlorohexane has been isolated (the product of hydrochlorination of the starting alkadiene). Low-temperature (190 K) structural examination of this centrosymmetrical molecule indicates that the unit cell comprises one molecule.