The Crystal Structure of trans-2,2′-Azoquinoxaline

The structure of the title compound obtained from 2(1H)-quinoxalinone oxime by the template effect of Co(II) and Ni(II) ion has been determined by three dimensional X-ray analysis.     

Crystal structures and theoretical calculations of trans-2,4,4-trimethyl-4-silathiane 1-oxide and 4,4-dimethyl-4-silathiane 1,1-dioxide

The crystal and molecular structures of trans-2,4,4-trimethyl-4-silathiane 1-oxide 1 and 4,4-dimethyl-4-silathiane 1,1-dioxide 2 were determined by single crystal X-ray diffraction. Both compounds have the chair conformation with the 2-Me and the S=O group in compound 1 occupying the equatorial positions. The DFT (B3LYP/6-311G(d,p)) and MP2 (MP2/6-311G(d,p)) theoretical calculations nicely reproduce the X-ray experimental geometry. The obtained results are discussed in connection with the electronic and structural properties of the compounds.

Crystal structures of rhodacyclopentane derivatives

Two complexes containing a rhodacyclopentane ring, viz. (acac)Rh(C₆H₈)(py)₂ and (acac)₂Rh₂(C₆H₈)(PPh₃) have been studied by X-ray diffraction. The ring forms through oxidative coupling of two allene molecules giving the structure A with trivalent, octahedrally-coordinated rhodium. In the second complex the unsaturated hydrocarbon part is also π-bonded to another Rh atom, and one acac group acts as a five-electron donor.     

Crystal structures of vasicinone and peganidine hydrochloride

Crystal structures of the alkaloids vasicinone and peganidine hydrochloride were studied by x-ray structure analysis. The configurations of asymmetric centers C4 and C9 in peganidine were determined. The hydroxyl and acetonyl groups were mutually syn-positioned relative to the tricyclic plane. H-bonds involving the Cl ion, which connected molecular cations transformed by 2₁ screw axes, were formed in the peganidine hydrochloride crystal. H-bonds between the C4 carbonyl and the C9 hydroxyl transformed by a glide plane were formed in the vasicinone crystal. The N1 atom was not involved in forming intermolecular H-bonds.     

Molecular structures and compositions of trans-1,2-dichlorocyclohexane and trans-1,2-difluorocyclohexane in the gas phase: an electron-diffraction investigation

The structures and compositions of gaseous trans-1,2-dichloro- (DCCH) and trans-1,2-difluorocyclohexane (DFCH), each of which may exist with the halogen atoms in a diaxial (aa) or diequatorial (ee) conformation, have been investigated by electron diffraction. The analysis was aided by rotational constants from microwave spectroscopy for the ee form of DFCH and by ab initio and density functional theory molecular orbital calculations for all species. The skeletons of the molecules have similar parameter values, but for the Cl-C-C-Cl and F-C-C-F fragments there are significant differences between the corresponding C-C-X bond angles and the X-C-C-X torsion angles in the two systems. There are also significant differences between the values of these parameters in the aa and ee forms of the same system. The composition of DCCH at 100 degrees C was measured to be 60(4)% aa, and that of DFCH at 70 degrees C was 42(7)% aa; the uncertainties are estimated 2sigma. From the preferred B3LYP/aug-cc-pVTZ calculations, the predicted theoretical composition is 51.2% aa for DCCH and 40.8% aa for DFCH. (Calculations at the levels B3LYP/6-31G(d) and MP2/6-31G(d) give similar results for DCCH, but both predict more aa than ee for DFCH.) Values (r(g)/A and angle(alpha)/degree) for some of the more important parameters of the aa/ee forms of DCCH are = 1.525(4)/1.525(6), C-Cl = 1.806(2)/1.787(2), angleC2-C1-Cl = 107.3(3)/111.5(3), angleC1-C2-C3 = 113.9(5)/111.6(5), angleC2-C3-C4 = 111.3(12)/109.9(12), and Cl-C2-C3-Cl = 165.3(9)/-59.4(9); and for DFCH C-C = 1.525(6)/1.520(9), C-F = 1.398(2)/1.390(2), angleC2-C1-F = 106.5(6)/109.2(6), angleC1-C2-C3 = 111.4(9)/110.9(9), angleC2-C3-C4 = 113.1(10)/113.1(10), and F-C2-C3-F = 171.1(37)/-67.2(37). The structures and compositions are discussed.     

Crystal structures of cesium and rubidium chlorites

Rubidium and cesium chlorites are prepared and studied by single crystal and powder X-ray diffraction. The compounds are isostructural; crystallize in the orthorhombic system; space group Cmcm, Z = 4. Unit cell parameters: a = 6.3464(8) Å, b = 6.4223(8) Å, c = 7.7493(9) Å for RbClO₂ and a = 6.5998(9) Å, b = 6.6116(9) Å, c = 8.3161(11) Å for CsClO₂. The structures can be represented as 3D frameworks formed by metal cations and chlorite anions acting as tetradentate bridging and bidentate chelating oxygen ligands.     

Crystal structures of deoxyvasicinone and its salts

The structures of the alkaloid deoxyvasicinone and of its complexes with HCl and CoCl₂·2HCl have been established by the method of x-ray structural investigation. The formation of complex salts of deoxyvasicinone differs from that of alkaloids with similar structures - peganine and deoxypeganine.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 89 14 75. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 849–854, November-December, 1995. Original article submitted April 17, 1995.     

Crystal structures of tungsten disulfide and diselenide

The crystal structures of the 2H- and 3R-forms of WS₂ have been refined from single-crystal data. The results are summarized and the interatomic distances are compared with those in related compounds.     

Crystal structures of tropylium perchlorate and iodide

Russian Chemical Bulletin -     

电子辐照对聚反式1,4-丁二烯晶型转变的影响

由于晶体结构对高分子性能有较大影响,因此研究其晶体结构具有重要意义．目前,已发现聚反式１,４－丁二烯（ＰＴＢＤ）存在两种晶型结构［１］,分别为单斜相和六方相,在低温下主要为单斜相,高温下主要为六方相．在一定温度下,单斜相和六方相可发生可逆的相转变［２］．本文以透射电镜为主要手段,在电子射线辐照下,研究单斜相向六方相的转变过程,不仅摄得样品的单斜相和六方相电子衍射谱,而且还拍摄到两相共存的电子衍射谱．１　ＰＴＢＤ的晶型转变Ｆｉｇ．１　ＤＳＣｔｈｅｒｍａｌｇｒａｍｏｆＰＴＢＤＳｃａｎｒａｔｅ：１０℃…