Synthesis of polyolefins with unique properties by using metallocene-type catalysts

Copolymerization of ethylene and 1,5-hexadiene (HD) by zirconocene catalysts proceeded via cyclization-addition mechanism to form 1,3-didsubstituted cyclopentane structure in the polyethylene chain. The 1,3-cyclopentane structure was found to be taken in the crystalline structure of polyethylene (isomorphism) by partially chainging the trans zigzag chain into gauche conformation, thereby, inducing a transformation of orthorhombic crystal to pseudohexagonal crystal. Copolymerization of ethylene and cyclopentene (CPE) by zirconocene catalysts yielded copolymers having 1,2-disubstituted cyclopentane structure in the polyethylene chain. The 1,2-cyclopentane structure was not taken into the crystalline structure of polyethylene. The melting point (T_m) and the crystallinity (X_c) of polyethylene decreased by copolymerization of HD or CPE, and the T_m- and X_c-decreasing effect of CPE was stronger than HD. For copolymers of propylene and HD or CPE obtained with isospecific zirconocene catalyst, the isomorphism was not ovserved.     

On the structure of the diagonal conditions

Some structural features of the diagonal problem of reduced density matrix theory are investigated by considering the cone B^r introduced elsewhere. In some special cases, we discover a very tight connection between the group structure of G^r, the invariance group of B^r, and the convex structure of B^r. We also state a general theorem that relates the convex structure of B^r to the group structure of G^r.     

Polymerization of acetylenic derivatives. XXVII. Synthesis and properties of isomeric poly-N-ethynylcarbazole

Poly-N-ethynylcarbazole (PEC) was prepared thermally, by using Ziegler-Natta catalysts, and also by using TiCl₄ and phosphine complexes for initiation. The spectral data (infrared, NMR, x-ray diffraction, and ultraviolet) were best interpreted based on a cis-transoidal/cis-cisoidal stereoblock structure for (both soluble and insoluble) polymers prepared by Ziegler-Natta catalysts and on a trans-cisoidal structure for the polymers prepared with the other catalysts. The cis-transoidal/cis-cisoidal stereoblock structure isomerized thermally into a trans-cisoidal structure, at temperatures which were dependent on the type of initiation.     

Study of alkaloids from the flora of the Siberian and Altai regions. 6. Crystal and molecular structure of songorine Z-oxime

Oximation of songorine afforded a mixture of its Z- and E-oximes. The crystal and molecular structure of the Z-isomer was established by X-ray diffraction analysis. Its structure was also confirmed by the spectral data (2D ¹H—¹H and ¹³C—¹H NMR spectroscopy and mass spectrometry). The structure of isomeric E-oxime was established by comparing its NMR spectroscopic data (¹H and ¹³C) with the data for the Z-isomer.     

Phase transitions and twinned low‐temperature structures of tetraethylammonium tetrachloridoferrate(III)

The title compound, [(C₂H₅)₄N][FeCl₄], has at room temperature a disordered structure in the high‐hexagonal space group P6₃mc. At 230 K, the structure is merohedrally twinned in the low‐hexagonal space group P6₃. The volume has increased by a factor of 9 with respect to the room‐temperature structure. At 170 and 110 K, the structure is identical in the orthorhombic space group Pca2₁ and twinned by reticular pseudomerohedry. The volume has doubled with respect to the room‐temperature structure. All three space groups, viz. P6₃mc, P6₃ and Pca2₁, are polar and the direction of the polar axis is not affected by the twinning. In the P6₃ and Pca2₁ structures, all cations and anions are well ordered.     

Preparation and Crystal Structures of some Binary Pnictides of Scandium,Zirconium, and Hafnium: Sc5Bi3, ZrBi, α‐HfSb,HfBi, HfBi2, and the Compound Zr5Bi3X1–x,Possibly Stabilized by an Impurity (X)

The title compounds were prepared by reaction of the elemental components. Of these Sc₅Bi₃ is a new compound. Its orthorhombic β‐Yb₅Sb₃ type crystal structure was determined from single‐crystal X‐ray data: Pnma, a = 1124.4(1) pm, b = 888.6(1) pm, c = 777.2(1) pm, R = 0.024 for 1140 structure factors and 44 variable parameters. For the other compounds we have established the crystal structures. ZrBi has ZrSb type structure with a noticeable homogeneity range. This structure type was also found for the low temperature (α) form of HfSb and for HfBi. For α‐HfSb this structure was refined from single‐crystal X‐ray data: Cmcm, a = 377.07(4) pm, b = 1034.7(1) pm, c = 1388.7(1) pm, R = 0.043 for 432 F values and 22 variables. HfBi₂ has TiAs₂ type structure: Pnnm, a = 1014.2(2) pm, b = 1563.9(3) pm, c = 396.7(1) pm. The structure was refined from single‐crystal data to a residual of R = 0.074 for 1038 F values and 40 variables. In addition, a zirconium bismuthide, possibly stabilized by light impurity elements X and crystallizing with the hexagonal Mo₅Si₃C_1–x type structure, was observed: Zr₅Bi₃X_1–x, a = 873.51(6) pm, c = 599.08(5) pm. The positions of the heavy atoms of this structure were refined from X‐ray powder film data. Various aspects of impurity stabilization of intermetallics are discussed.     

The thallium tungstate Tl2W4O13: A tunnel structure related to the hexagonal tungsten bronze

The crystal structure of thallium tungstate Tl₂W₄O₁₃ (a = 7.327Å; b = 37.864 Å; c = 3.840 Å; space group Pmab) has been resolved by three-dimensional single-crystal X-ray analysis. The average structure was resolved by standard Patterson and Fourier techniques and refined by full-matrix least squares to final agreement indices R = 0.087 and R_w = 0.100. Superstructure reflections referred to a supercell (a, b, 2c; space group Pcab) led to a framework model which is described. The structure consists of corner-sharing chains of WO₆ octahedra parallel to a and c axes. Hexagonal and pentagonal tunnels, bound by these chains, are filled by thallium atoms. The atomic arrangement is closely related to the hexagonal bronze structure. The tungstate Tl₂W₄O₁₃ can thus be considered as a member of a series of phases (TlB₃X₉)_n · Tl₆B₁₀X₃₄ (X = O, F) involving hexagonal tungsten bronze ribbons.     

Poly(β-Amino acids). V. Synthesis and conformation of oligomeric α-isobutyl-L-aspartate

α-Isobutyl-L -aspartate oligomers, Z-(α-i-Bu-Asp)_2n–OEt (n = 1–5), where Z = benzyloxycarbonyl and OEt = ethyl ester, were prepared stepwise, and their conformation in solution was investigated by optical rotation, circular dichroism (CD), and NMR spectroscopy. The oligomers up to hexamer existed only in a disordered form. An ordered structure began to appear at octamer and decamer in chloroform and 2,2,2-trifluoroethanol. The ordered structure was more favorable for N-unprotected oligomers, H-(α-i-Bu-Asp)_2n–OEt, in comparison with the corresponding Z-(α-i-Bu-Asp)_2n–OEt. The effects of oligomer concentration and temperature on the structure were slightly observed. The most likely ordered structure was a β form caused by intramolecular association.     

1,5‐Dianilinopentane‐1,3,5‐trione: a crystal structure containing two polymorphic domains

Single crystals of the title compound, C₁₇H₁₆N₂O₃, were obtained by gas diffusion. The observed diffraction pattern is compatible with a superposition of reflections from two monoclinic unit cells with the space group C2/c. The two cells share the a and b axes but not the c axis. Both structures contain layers parallel to (001), with molecules connected by intermolecular N—H...O=C hydrogen bonds. The bonding between adjacent layers is weak. Layer displacements result in a crystal structure containing two closely related polymorphic domains. The structure of one polymorph can be derived from the structure of the other if subsequent layers are displaced by (a/4, b/4, 0) for odd‐numbered layers and by (a/4, −b/4, 0) for even‐numbered layers. Three different crystals were analysed and their observed diffraction patterns were similar, showing all three crystals to contain the polymorphic domain structure.     

An X-Ray and Electron Diffraction Study of the Tetragonal Lead Tungsten Bronze Pb0.26WO3

The average structure of the tetragonal lead tungsten bronze, Pb_0.26WO₃, has been determined by single-crystal X-ray diffraction (P4/mbmspace group,a_av=12.217(1)Å ,c_av=3.7828(7)Å andZ=10). The structure refinement based on 370 observed unique reflections (2539 totally measured reflections) withF_o>4σ(F_o) converged toR=0.035 (R_w=0.031). All but one of the oxygen atoms exhibit a twofold disorder. The lead atoms are distributed over three, symmetrically independent, positions inside the pentagonal tunnels. Electron diffraction observations recognize the X-ray average structure. Furthermore, satellite spots appear on the ED patterns revealing a modulated structure, which may be described in terms of a periodic repetition of antiphase boundary planes inside a superstructure related to the average structure by andc_s=2c_av. The repetition distance isd=5/2a_sand the displacement vector is R= 1/2 a_av.     

Crystal Structure and Packing of Isocyclosporin A

The crystal structure of isocyclosporin A ( 1 ), a rearrangement product of the immunosuppressant drug cyclosporin A, has been determined at 193 (2) K. Crystals are orthorhombic with cell dimensions a = 26.684 (7), b = 26.936 (3) Å, c = 28.549 (7) Å, space group C222₁. The structure was solved by direct methods and refined by full-matrix least-squares methods to a conventional R value of 0.110. In contrast to the structure of cyclosprin A in solution and in the crystal, isocyclosporin A ( 1 ) has no regular secondary structural elements. The backbone adopts an open, irregular conformation with cis amide bonds between residue 2 and 3, and 3 and 4, respectively. All the other amide bonds and the ester linkage are trans. Contrary to crystal structures of cyclosporin derivatives, this crystal structure is stabilized by two transannular and four intermolecular H-bonds.     

K3TaF8 from laboratory X‐ray powder data

The crystal structure of tripotassium octafluoridotantalate, K₃TaF₈, determined from laboratory powder diffraction data by the simulated annealing method and refined by total energy minimization in the solid state, is built from discrete potassium cations, fluoride anions and monocapped trigonal–prismatic [TaF₇]²⁻ ions. All six atoms in the asymmetric unit are in special positions of the P6₃mc space group: the Ta and one F atom in the 2b (3m) sites, the K and two F atoms in the 6c (m) sites, and one F atom in the 2a (3m) site. The structure consists of face‐sharing K₆ octahedra with a fluoride anion at the center of each octahedron, forming chains of composition [FK₃]²⁺ running along [001] with isolated [TaF₇]²⁻ trigonal prisms in between. The structure of the title compound is different from the reported structure of Na₃TaF₈ and represents a new structure type.     

The Molecular and Crystal Structure of the Glycopeptide A-40926 Aglycone

The crystal structure of a glycopeptide antibiotic A–40926 aglycone was investigated by X-ray analysis at ?120°. A-40926 crystallises in the orthorhombic space group P2₁2₁2₁ with two monomers in the asymmetric unit, a = 21.774(4), b = 28.603(7), c = 29.757(4) Å. ‘Conventional’ direct methods approach failed to solve the structure, but a novel iterative real/reciprocal space procedure was successful. Refinement against 11248 F² data led to R1 = 13.3% for 6770 F > 4σ (F). The two monomers of A-40926 have similar conformations and are bound by antiparallel H-bonds to form a ‘chain’ structure of connecting dimers. The antibiotic molecule possesses a ‘binding pocket’ for the C-terminal carboxy group of the cell-wall protein, which is consisten with suggestions based on NMR data and the recently reported crystal structure of ureido-balhimycin. In A-40926 the monomers are polymerically linked by H-bonds, quite unlike the tight dimer formation observed in ureido-balhimycin.     

Zintl‐Phase Sr3LiAs2H: Crystal Structure and Chemical Bonding Analysis by the Electron Localizability Approach

The compound Sr₃LiAs₂H was synthesized by reaction of elemental strontium, lithium, and arsenic, as well as LiH as hydrogen source. The crystal structure was determined by single‐crystal X‐ray diffraction: space group Pnma; Pearson symbol oP28; a = 12.0340(7), b = 4.4698(2), c = 12.5907(5) Å; V = 677.2(1) ų; R_F = 0.047 for 1021 reflections and with 36 parameters refined. The positions of the hydrogen atoms were first revealed by the electron localizability indicator and subsequently confirmed by crystal structure refinement. In the crystal structure of Sr₃LiAs₂H the metal atoms are arranged in a Gd₃NiSi₂‐type motif, whereas the hydrogen atoms are arranged in a distorted tetrahedral environment formed by strontium. The calculated band structure revealed that Sr₃LiAs₂H is a semiconductor, which is in agreement with its diamagnetic behavior. Thus, Sr₃LiAs₂H is considered as a (charge‐balanced) Zintl phase.     

Amido acids of norbornene series in reactions with sulfonyl azides

In reaction of amido acids from the norbornene series with arenesunfonyl azides alongside the expected N,N-dialkyl-5-oxo-exo-2-arylsulfonylamino-4-oxatricyclo[4.2.1.0^3,7]nonane-endo-9-carboxamides (oxabrendanones) the formation of zwitter-ions with a structure of 5-(N,N-dialkyliminio)-exo-2-arylsulfonylamino-4-oxatricyclo[4.2.1.0^3,7]nonane-endo-9-carboxylates came as a surprise. The structure of compounds obtained was confirmed by the analysis of their IR and ¹H NMR spectra. The molecular structure of one among the zwitterions was established by XRD analysis.     

The crystal structure of 1,4-benzenedithiol by rietveld analysis and studies on the mechanism of solid-state addition polymerization of 1,4-benzenedithiol to 1,4-diethynylbenzene

The crystal structure of 1,4-benzenedithiol (BDT) was determined by the Rietveld method based on the calculation of the atomic coordinates of the BDT molecule using the Molecular Mechanics Program (MMP2). The refined crystal structure of BDT was monoclinic P₂₁/c with dimensions, a = 7.795, b = 7.290, c = 5.955 Å, β = 92.16°, z = 2. The R factor of the refined structure was 0.038. Using above results, the mechanism of solid-state addition polymerization of BDT to 1,4-diethynylbenzene (DEB) was studied. Sublimed BDT piles up onto glass plate substrate and forms the layer structure along with the a axis. An inclination angle of the piled BDT column was 60° toward the substrate surface. DEB crystal structure was also monoclinic P₂₁/c with a = 4.007, b = 6.018; c = 15.340 Å, β = 91.42°, z = 2. Sublimation of equimolar mixture of BDT and DEB gave a crystal having 1 : 1 composition, in which DEB column is situated between the columns of BDT. Relative arrangement of both monomers was suitable for the addition of  SH and  CCH groups, since the distance between the two groups is 3.3 Å by CERIUS II calculation. Therefore, the addition polymerization of BDT to DEB easily proceeded by UV irradiation and the resulting polymer had a highly layer structure along with the a axis of BDT crystal. Tentatively estimated crystal structure of polymer obtained is monoclinic with a = 7.73, b = 7.30, c = 5.95 Å, β = 92.16°. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 1621–1625, 1997     

Three Inter‐Alkali Metal Acetylides: KNaC2, KRbC2, and NaRbC2: Syntheses,Crystal Structures,and Structural Systematics

Three alkali metal acetylides, namely KNaC₂, KRbC₂, and NaRbC₂, were synthesized and characterized by means of X‐ray powder diffraction. KNaC₂ and KRbC₂ crystallize as a variant of the anti‐PbCl₂‐type structure (Pnma, Z = 4), whereas NaRbC₂ crystallizes as a variant of the anti‐PbFCl‐type structure (Pmmn, Z = 2). Based on a simple systematic approach developed by Sabrowsky et al. for inter‐alkali metal chalcogenides all known inter‐alkali metal acetylides can be classified into two classes: variants of the anti‐PbCl₂ type structure and variants of the anti‐PbFCl type structure. Acetylides with Q(ABC₂) ≤ 1.45 crystallize in the anti‐PbCl₂‐type structure, whereas for Q(ABC₂) > 1.45 the anti‐PbFCl‐type structure is found (Q(ABC₂) = V_m(A₂C₂)/V_m(B₂C₂) with V_m(A₂C₂) > V_m(B₂C₂); V_m: molar volume, A, B = alkali metals).     

Synthesis and Structure Investigation of a Novel 3-Dimensional Potassium Supermolecular Compound Based on 2,4-Dinitro Resorcinol

A novel 3‐dimensional potassium supermolecular compound [K(HDNR)(H₂DNR)(H₂O)]_n (H₂DNR?2,4‐dinitro resorcinol) was synthesized and characterized by elemental analysis and FT‐IR spectroscopy. The crystal structure investigated by X‐ray single crystal diffraction shows that [K(HDNR)(H₂DNR)(H₂O)]_n crystallizes with a monoclinic unit cell in the space group P2(1)/c with unit cell dimensions of a=17.648(5) Å, b=12.527(3) Å, c=7.735(2) Å, β=94.33(2)°, V=1705.00(73) ų, Z=4. The structure was refined to the final R=0.0670 and wR=0.0722 for 2022 observed reflections with I>2σ(I). In the compound, potassium cation is assembled into one‐dimensional chains along c‐axis through oxygen atoms from water molecules, and the chains were connected by the bridged HDNR^? anions to form a two‐dimensional net structure. The two‐dimensional nets constructed a three‐dimensional supramolecular architecture via intermolecular hydrogen bonds and N–O···π interaction. Density functional theory (DFT) B3LYP was employed to optimize the structure and calculate energies for three tautomers of HDNR^? univalent anion. Three stable tautomers were located. It was found that the structure (I) with O(1) losing hydrogen atom is more stable than the structure (II) also with O(1) losing hydrogen atom and the structure (III) with O(4) losing hydrogen atom.     

Superstructure and stacking faults in hydrothermal-grown KBe2BO3F2 crystals

The structure of the hydrothermal-grown nonlinear optical crystal KBe₂BO₃F₂ was investigated. A new structure of the R3?c space group with cell parameters of a=4.422(1) Å and c=37.524(3) Å was obtained by powder X-ray diffraction and Rietveld refinement. The new structure is a 1×1×2 superstructure of the previously reported R32 structure with a different stacking sequence of (Be₂BO₃F₂)_∞ layers along the c axis. The relationship between the refined structure and the experimental results is discussed. A stacking fault mechanism is proposed for the formation of the superstructure as well as the nonuniformity of the hydrothermal-grown KBBF crystals.     

NMR studies of polymer solutions. III. Conformational transition study of oligomeric polyethylene in mixed solvents

The intramolecular structure of oligomeric polyethylene (PE) in solvent mixtures of α-chloronaphthalene and carbon tetrachloride, α-chloronaphthalene and deuterated octane, and α-chloronaphthalene and deuterated hexadecane was studied at 35°C. by a high-resolution nuclear magnetic resonance technique. It was clearly shown that the n-alkanes show no detectable selective solvent absorption in these systems. The conformational structure (P_p), which was formed in “bulky” aromatic solvents when the chain length was greater than 16, was significantly destroyed by the presence of carbon tetrachloride, octane, or hexadecane in the above-mentioned solvent mixtures. Therefore, the “bulky” aromatic solvents, such as α-chloronaphthalene and 9-chloroanthracene, can be classified as P_p-structure-promoting solvents, in which the PE remains in the P_p conformation. In contrast, carbon tetrachloride and linear alkanes are P_m-structure-promoting solvents, in which the PE does not exhibit any P_p structure but is in the disordered P_m conformation. It is speculated that the P_p structure is caused by a “chain-fold” mechanism.