Effect of Methyl Substitution on Molecular Shapes and Dimensions of Phenanthrenes and Benz[a]anthracenes

For polynuclear aromatic hydrocarbons (PAH) such as the benz[a]anthracenes (BA), carcinogenic activity is appreciably influenced by the numbers and positions of methyl and other substituents and hence by the molecular shapes. The planarities and dimensions, as determined by X-ray single-crystal structure analyses, of methyl-substituted BA and related PAH, including methyl phenanthrenes (MP) which also contain the carcinogenically important bay and K regions, are compared.

BA molecules with substituents well removed from the bay region, including those substituted at 5 or 6 (the K region), are nearly, but not quite, planar, with a mutual inclination of several degrees between A and C rings on each side of the bay region. With one or both bay positions 1 and 12 methyl-substituted, distortion is much greater (A/C up to 29° in 1,12-dimethyl BA). For phenanthrenes, the presence of the two methyl substituents in the bay, as in 2,4,5,7-tetra MP, can lead to A/C of 28° compared with the very small (2°) mutual inclination in 9,10-di MP. In the bay regions of all the PAH studied, the beach C–C bond is typically as long as 1.45–1.46 Å and the beach C–C–C bond angles are enlarged to 122–123°.     

X-ray crystal structure of the dye 2-cyano-4-bromo-4′-N,N-diethylaminoazobenzene

The crystal structure and molecular conformation of 2-cyano-4-bromo-4′-N,N-diethylaminoazobenzene (C₁₇H₁₇N₄Br, mol. wt. = 357·2 a.m.u) has been determined from X-ray diffraction data; triclinic, P$\text{1}$ (No. 2), a = 10·132(11) Å, b = 12·216(16) Å, c = 6·966(11) Å, α = 104·21(9)°, β = 92·67(12)°, γ = 97·22(7)°, V = 826·5(9) ų, Z = 2, D_c = 1·436 g cm^?3, F(000) = 378, λ(MoKα) = 0·71069 Å, μ(MoKα) = 26·0 cm^?1. The structure was solved by the multiple solution direct method and refined by full-matrix least-squares to R = 0·059 for 1538 independent observed reflections. The azobenzene skeleton is planar to within 0·06 Å. Most significant bonding data are: NN, 1·290(8) Å; BrC, 1·866(6) Å; mean CN (azo) 1·380(8) Å; NNC, 113·6(4) and 115·3(4)°; NCC (cis relative to NN) 125·9(4)° and 126·7(4)°; NCC (trans) 116·8°(5)° and 116·1(4)°.     

Topochemistry. Part XXXVII. The Crystal Structure of Dibenzoyldiimide

The crystal and molecular structures of dibenzoyldiimide, C₆H₅CO–N = N–COC₆H₅, have been determined by SEARCH as part of a study of the solid state photochemistry of α-carbonyl-azo-compounds. Partial three-dimensional data were refined with anisotropic temperature factors of the heavy atoms to r = 0.031 and R = 0.080. The bond lengths and angles have been measured with estimated standard deviations of 0.01 A and 0.6°. As the result of rotation around the C–N bonds, the interplanar distance of the parallel benzoyl groups of the (centro-symmetric) trans-molecule is 1.02 Å. Photochemical rearrangement paths are discussed in terms of contact geometry.     

X-ray crystal structure of the dye 2-bromo-4-cyano-4′-N,N-diethylaminoazobenzene

The crystal structure of 2-bromo-4-cyano-4′-N,N-diethylaminoazobenzene has been determined from X-ray diffraction data: C₁₇H₁₇N₄Br, mol. wt = 357·1. Triclinic, Pī (No. 2), α = 13·162(5) Å, b = 7·516(3) Å, c = 8·496(4) Å, α = 101·63(4)°, β = 95·79(4)°, γ = 91·49(4)°, V = 818·10 ų, Z = 2, D_c = 1·45 g cm^?3, F(000) = 378, λ(Mo_Kz) = 0·7107 Å, μ(Mo_Kα) = 26·70 cm^?1. The structure was solved by direct methods and refined by full-matrix least-squares to R = 0·053 for 2081 independent reflexions. The molecule possesses an essentially planar azobenzene skeleton. The effects of substituents on the geometry of the azo group are discussed. Significant molecular parameters are: NN, 1·264(6) Å; ₁BrC, 1·904(5) Å; mean NC, 1·410(7) Å; NNC, 115·7(2)° and 113·0(2)°; NCC (cis relative to NN), 125·4(3)° and 123·1(2)°; CC(Br)C, 123·0(2)°.     

X-Ray crystal structure of the Dye 2,4,6-Tricyano-4'-N,N-diethylaminoazobenzene

The crystal structure and molecular conformation of 2,4,6-tricyano-4'-N,N-diethylaminoazobenzene (C₁₉H₁₆N₆, mol. wt. 328.4a.m.u.) has been determined from X-ray diffraction data: monoclinic P2₁/c, a = 9.302(7)Å, b = 8.733(5)Å, c = 20.98(1) Å, β = 94.93(6)°, V = 1699(2)ų, Z = 4, D_c = 1.284gem^?3, F(000) = 688, λ(MoKα) = 0-71069Å, μ(MoKα) = 0.76cm^?1. The structure was solved by MULTAN andrefined by full-matrix least-squares toR = 0.050 for 1358 independent observed reflections. The azobenzene skeleton is planar to within 0.12Å. Most significant bonding data are: NN, 1.286(4) Å; mean C-N (azo) 1.383(4) Å; mean C-C (cyano) 1.439(5) Å; mean CN 1.146(5)Å; NN-C, 112.8(2)° and 115.9(2)°; N-C-C (cis relative to NN) 127.6(2)° and 124.3(2)° ; N- C- C(trans) 115.2(2)° and 117.7(2)°.     

Synthesis,structural and spectroscopic studies of 1-(2-FUROYL)-3-phenylthiourea: a theoretical and experimental approach

The thiourea derivative 1-(2-Furoyl)-3-phenylthiourea (FPT) was synthesized and characterized by using spectroscopic (IR, Raman, UV–VIS, ¹H and ¹³C NMR) and structural methods (powder X-ray diffraction data). The experimental measurements were complemented with quantum chemical calculations. FPT crystallizes in the monoclinic crystal system, space group P21/c, with cell parameters a?=?4.7679(5) Å, b?=?20.9704(2) Å, c?=?12.5109(5) Å and β?=?109.811(10)°, V?=?1176.87(3) ų. In the crystal structure, the thiourea group makes dihedral angle of 43.8(5)° with the furoyl group, whereas the benzene ring is inclined by 24.3(4)°. The anti-syn geometry of the thiourea unit is stabilized by intramolecular N–H^?…?O hydrogen bond between the H atom of the syn thioamide and the carbonyl O atom. In the crystal structure, molecules of FPT are packed through N–H···S, C–H···O and C–H···C hydrogen bonds, and a π–π interaction with offset arrangement. Hirshfeld surface analysis was performed in order to evaluate and quantify intermolecular interactions. The Hirshfeld surface analysis indicated that the H···H interactions comprise the majority of interactions. Shape index and curvedness clearly indicate π–π interactions in the compound FPT.     

Structure of the dye 2,6-dichloro-4′-N,N-diethylaminoazobenzene

The structure of 2,6-dichloro-4′-N,N-diethylaminoazobenzene has been determined from X-ray diffractometer data: C₁₆H₁₇Cl₂N₃, MW = 322·2, monoclinic, P2₁/n, a = 11·160 (2), b = 12·066 (2), c = 13·633 (3) Å, β = 116·46 (2)°, V = 1643·5 ų, Z = 4, D_c = 1·30 g cm^?3, F(000) = 672, λ(MoKα) = 0·71069 Å, μ(MoKα) = 3·94 cm^?1. The structure was solved by direct methods and refined to R = 0·073 for 1495 independent reflexions. The molecule is non-planar with a dihedral angle of 87·8° between the phenyl rings. The effects of substituents on the aromatic ring geometry are discussed. Significant molecular parameters are: NN, 1·164 (9) Å; mean ClC, 1·741 (6) Å; mean CN(azo), 1·487 (9) Å; NNC, 112·4 (2)° and 109·1 (2)°; NCC (cis relative to NN), 125·5 (3)° and 122·4 (2)°; NCC (trans relative to NN) 114·0 (3)° and 119·5 (3)°; mean CC(Cl)C, 122·3 (3)°.     

Stereochemische Untersuchungen heterocyclischer Verbindungen. XII. Kristall- und Molekülstruktur von 1-(2-Amino-1-cyano-2-thio-ethylen)pyridiniumyliden

Stereochemical Investigations of Heterocyclic Compounds. XII. Structural Investigations of 1-(2-Amino-1-cyano-2-thio)ethene Pyridinium Ylides Two isomerization processes were found by ¹H-d-n. m. r. characterized by ΔG^* = 67 ± 4 KJ/mol for E- Z-isomerization and ΔG^* = 46 ± 5 KJ/mol for the hindered rotation of the pyridine substituent in 1a . The structure of 1b was solved by direct method. Crystals are monoclinic space group P2₁/n, a = 13.682(3), b = 9.452(1), C = 19.713(6) Å, β = 96.42(2)°, V = 2533.3 ų, D_x = 1.328 Mg · m⁻³, Z = 8. Both E- and Z-isomeres of 2b are found in the crystal lattice. The amino C distance with 1.369 (1,387) Å is shorter than the theoretical single bond distance. The formal  CC double bond with 1.377 (1.391) Å is considerably longer than 1.337 Å observed in the some alkenes.     

Crystal Structure and Computational Analysis of a Two-Dimensional Coordination Polymer,BiI<Subscript>3</Subscript>(DppeO<Subscript>2</Subscript>)<Subscript>3/2</Subscript>

Catena-poly[fac-triiodobismuth(III)-tris-(µ-ethane-1,2-diylbis(diphenylphosphane oxide-κ²O,O′))], a 2-D sheet network of BiI₃ was synthesized from BiI₃ and ethane-1,2-diylbis(diphenylphosphane oxide) (DppeO₂) in tetrahydrofuran. The crystal structure revealed a trigonal structure with three-fold symmetry at Bi. Bismuth centers show fac-BiI₃O₃ coordination, with Bi–I?=?2.9416(2) Å and Bi–O?=?2.4583(17) Å. The I–Bi–I and O–Bi–O angles (95.520(7)° and 79.04(6)°, respectively) indicate trigonal distortion in the Bi octahedron. Bridging DppeO₂ ligands centered on inversion centers give rise to a 2-D sheet polymer. The 8.3 Å thick sheets consist of three layers in a sandwich structure. The outer layers are composed of phenyl rings and BiI₃ groups with the iodide atoms pointing outward. The central layer consists of the O=PCH₂CH₂P=O bridging groups. Computational results suggest that semi-conducting behavior arises from Bi(III) centers. A halide to DppeO₂ π* transition is suggested by theoretical results.     

Passive behaviour of niobium

The passive behaviour of niobium at electrode potentials from −1 to 4 V (sce) in aqueous solutions of pH 0–13 at 25°C has been studied by quasi-steady (20 h) and transient polarization measurements, dc capacitance determinations and some AES depth profile investigations. Niobium exhibits a quasi-steady passive current varying little with the electrode potential and pH. After potential (or current) steps, transient superpolarization occurs. The transient data accord with the Cabrera-Mott equation and fit reasonably with λ = 1.5 Å and z = 5 for metal ion transfer at the metal—oxide interface. The capacitance data satisfy a simple insulator model, reveal the main charge distribution in the passive electrode, and combine with film thickness data to give ε = 46 for the static dielectric constant of the passive film. The anodization ratio is 37 Å V⁻¹ under quasi-steady conditions. The passive niobium electrode seems mostly to carry a net negative charge. Anodic oxygen evolution does not occur.     

Reversible Carbon-Carbon Bond Cleavage of a 3-Vinyl-1-Cyclopropene by Rh(I). Molecular Structures of Two Sterically Crowded 1,2,3,5-η-Pentadienediyl Complexes of Rh(III)

1,2,3-Tri-tert-butyl-3-vinyl-1-cyclopropene 6a reacts with [RhCl(C₂H₄)]₂ to give the dimeric 1,2,3,5-η-pentadienediyl complex 7a . The cyclopentadienyl derivative of this complex, 8a , is obtained by reaction of 7a with T1(C₅H₅). Crystal structures of both 7a and 8a were determined: 7a ; orthorhombic, Pbcn, a = 28.136 (4) Å, b = 10.637 (2) Å, c = 12.154 (2) Å, V = 3637.6 (1.2) ų, and Z = 4 : 8a ; triclinic, P 1 -bar, a = 9.906 (2) Å, b = 9.736 (2) Å, c = 12.126 (2) Å, α = 76.07 (2)°, β = 78.21 (2)°, γ = 65.34 (2)°, V = 1024.6 (3) ų, and Z = 2. Treatment of 7a with one equivalent of PMe₃ per Rh center results in regeneration of the vinylcyclopropene, demonstrating the reversibility of the ring opening reaction. Deuterium labelling studies show that both the ring opening and closing reactions proceed with retention of configuration at the vinyl olefin. Thus the trans-deuterated vinylcyclopropene 6b reacts with [RhCl(C₂H₄)₂]₂ to give 7b in which deuterium is located exclusively in the syn position. Treatment of 7b with T1(C₅H₅) yields 8b . Treatment of 7b with one equivalent of PMe₃ per Rh center results in formation of 6b as the sole organic product. Unlike their triphenyl relative 2 , the tri-Bu complexes 7a , 7b, 8a , and 8b are stereochemically rigid in solution at room temperature, and do not undergo an η³ → η¹ → η³ isomerization on the NMR time scale. However, after prolonged heating, syn-anti site exchange of H and D slowly takes place with 8b .     

Effects of annealing temperature on structural and photoluminescence properties of Eu,Dy and Sm doped CaWO4 nanoparticles

Nanoparticles of xRe₂O₃ – (100-x)CaWO₄ (Re = Eu, Dy, Sm; x = 0, 1, 3, 5, 7 and 10 mol%) were synthesized by solid-state sintering at two annealing temperatures of 800 °C and 1150 °C and characterized by neutron diffraction, Raman and photoluminescence (PL) spectroscopy. The samples are composite materials and contain tetragonal CaWO₄ and cubic Re₂O₃ phases. The unit cell parameters, atomic position co-ordinates, crystallite size, mole-fraction of phases, bond-lengths, bond-angles and cation-oxygen co-ordination numbers were determined by Rietveld analysis of the neutron diffraction data. The short-range structure of CaWO₄ consists of snub disphenoid deltahedral CaO₈ and tetrahedral WO₄ units and the structure of cubic Re₂O₃ consists of two types of ReO₆ units. All the W–O bonds in WO₄ units are of equal lengths (1.77–1.79 Å) whereas two kinds of slightly different Ca–O bond-lengths (2.41–2.45 Å and 2.45–2.47 Å) exist in CaO₈ units. The neutron pair distribution function of the undoped CaWO₄ samples shows the first peak in the range of 1.71–1.74 Å due to W–O bonds and the second peak at 2.84 Å due to O–O and Ca–O pair correlations. Raman studies of Eu-doped samples show only W–O vibration modes, however, Sm and Dy-doped CaWO₄ show weak Raman peaks of Sm₂O₃ and Dy₂O₃, along with W–O bond vibrations. PL studies show highest orange-red emission at 1 mol% Sm₂O₃, green emission at 1 mol% Dy₂O₃ and red emission at 3 mol% Eu₂O₃. The light emission intensity in all the samples increases with the increase in annealing temperature from 800 °C to 1150 °C.     

One-pot template synthesis and crystal structure of two new polyaza copper(II) complexes

A new 14-membered hexazamacrocyclic copper(II) complex [Cu(H₂L¹)](ClO₄)₄(L¹=1,8-bis(2-aminoethyl)-1,3,6,8,10,13-hexaazacyclotetradecane) has been prepared by the one-pot reaction of ethylenediamine and formaldehyde in the presence of the Cu(II) ion. The crystal structure of [Cu(H₂L¹)](ClO₄)₄ was determined by X-ray diffraction. It crystallizes in the triclinic space group P−1 with a=12.118(2) Å, b=12.438(2) Å, c=12.466(2) Å, α=102.26(1)°, β=112.82(1)°, γ=111.51(1)°, and Z=2. The coordination geometry around the copper(II) ions is axially elongated octahedral with four nitrogen atoms of the macrocycle [Cu–N 2.012(7) Å for Cu(1) and 2.013(6) Å for Cu(2), average value] and two oxygen atoms of two ClO₄⁻ anions [Cu–O=2.550 Å for Cu(1) and 2.601(6) Å for Cu(2)]. [CuL²](ClO₄)₂(L²=3,7-bis(2-aminoethyl)-1,3,5,7-tetraazabicyclo[3,3,2]decane) with a novel tetraazabicyclic ligand was obtained from the same reaction system as an additional product. Crystal structure of [CuL²](ClO₄)₂: monoclinic space group Cc, a=16.393(3) Å, b=8.8640(18) Å, c= 13.085(3) Å, β=105.01(3)°, and Z=4.     

Preparation and structural characterization of mercury 21-thiaporphyrin complex: HgII(Stpp)Cl (Stpp=tetraphenyl-21-thiaporphyrin anion)

Treatment of tetraphenyl-21-thiaporphyrin (StppH) with Hg(OAc)₂ in CH₂Cl₂ yields diamagnetic Hg^II(Stpp)Cl complex. The coordination sphere around Hg²⁺ in the monomeric molecule is described as a five-coordinate distorted trigonal bipyramid with the bonding to the three pyrrole nitrogens [Hg(1)–N=2.104(4), 2.626(4), 2.640(4) Å], the thiophene sulfur [Hg(1)–S=2.801(1) Å], and one axial chloride ligand [Hg(1)–Cl(1)=2.318(1) Å]. The plane of the three pyrrole nitrogen atoms [i.e., N(1), N(2), N(3)] bonded to Hg²⁺ is adopted as a reference plane 3N. Because of its larger size, the Hg²⁺ is considerably out of the 3N plane; its displacement of 1.41 Å is in the same direction as that of the apical Cl⁻ ligand. The thiophene ring is slightly folded so that the dihedral angle between the C(13)–C(14)–C(15)–C(16) and C(13)–S(1)–C(16) planes is 7.3°.     

Two intra-molecular inter-ligand C(aromatic)–H⋯O(carboxyl) interactions reinforce the formation of a single Cu(II)–N4(pza) bond in the molecular recognition between pyrazine-2-carboxamide (pza) and the (iminodiacetato)copper(II) chelate. Synthesis,molecular and crystal structure and properties of [Cu(IDA)(pza)(H2O)]·H2O

Aqua(pyrazine-2-carboxamide)(iminodiacetato)copper(II) monohydrate, [Cu(IDA)(pza)(H₂O)]·H₂O, was synthesised and characterised by thermal, spectral, magnetic and X-ray diffraction methods. Its crystal structure was solved to a final R1=0.058. The Cu(II) atom exhibits a square base pyramidal coordination (type 4+1) with IDA ligand in mer-tridentate configuration [Cu–N(aliphatic) 1.986(7), Cu–O(carboxyl) 1.933(6) and 1.938(5) Å], the Cu–N4(pza) bond [1.984(7) Å] and Cu–O(apical aqua) bond [2.347(8) Å]. The N4-monodentate ligand role of pza is in contrast with that of the N,O-bidentate pza-Cu(II) chelation in [Cu(pza)₂(ClO₄)₂] or [Cu(acac)(pza)(ClO₄)]·H₂O. In the molecular recognition between Cu(IDA) chelate and pza the Cu–N4(pyridine-like) coordination mode is preferred because it enables the additional contribution of two weak intra-molecular inter-ligand C(aromatic)–H⋯O (IDA) interactions.     

Effect of temperature on Nylon 6 fibers at different denier values and study of macromolecular parameters by SAXS technique

Small-angle X-ray scattering (SAXS) was used to evaluate various macromolecular parameters of Nylon 6 textile fiber at denier values of 15/1, 18/1, and 20/1 treated at different temperatures within the range of 20–63°C. The theories of Kratky, Porod, Bueche, and Wendorff were applied to the densely packed two-phase system of Nylon 6, which conforms to the general micelle system. The values determined for the parameters, such as microvoid dimensions (d), the void percentage (w₁), the length of coherence (lc), the specific inner surface (o/v), and the transversal lengths (l₁ and l₂) of Nylon 6 fiber at a denier value of (15/1) at temperature 38°C are 62.5 Å, 0.0181%, 480.55 Å, 3.214 × 10⁻⁶ Å⁻¹, and 225 Å and 1244 × 10³ Å, respectively. A comparative study of the above parameters at different temperatures was also made and a correlation was established. © 1998 John Wiley & Sons, Inc. J Appl Polm Sci 67:1753–1759, 1998     

The Crystal and Molecular Structure of 11-Chloro-3,8-Methano-[11] Annulenone

The crystal structure of a benzhomotropone, 11-chloro-3,8-methano-[11] annulenone, has been solved and refined to R = 4.5%. The crystals are monoclinic, a = 6.854, b = 7.681, c = 19.324 Å, β = 108.54°, spacegroup P2₁/c. The molecule exhibits alternation of bond lengths with evidence of slight π-electron delocalisation. Principal bond lengths are C?C(mean) 1.344, C? C(mean) 1.442, C? Cl 1.748 and C?O 1.231 Å     

Studies of the development of fibrillar structure in nylon 6

Very thin films of poly(vinyl alcohol) could be prepared by utilizing the adsorption of polymer molecules at air/water interface from the aqueous solutions of the poly(vinyl alcohol) derived from vinyl trifluoroacetate. The films prepared by the bubble method were thinner than those obtained by the frame method. The minimum thickness of the former films was 260 Å and that of the latter was 1800 Å. These very thin films resisted water at temperatures below 55°C. The maximum Young's modulus of the drawn/annealed films prepared from these samples was 30 GPa. The permeability of water, J_w/δP, was 2–6 × 10^?3 cm · s^?1 atm^?1 (0–55°C) for the untreated film (thickness: 1800 Å) prepared by the frame method and 0.8–2.2 × 10^?2cm · s^?1 · atm^?1 (5–55°C) for the untreated film (360 Å) prepared by the bubble method, and depended on the thickness of film.     

Synthesis and X-ray crystal structure of monomeric lanthanocene aryloxide complexes with a tridentate Schiff base ligand

Reaction of tris(cyclopentadienyl)lanthanide with the tridentate Schiff base N-1-(ortho-methoxyphenyl)salicylideneamine in THF at room temperature affords the isolation of monomeric lanthanocene Schiff base complexes, (η⁵-C₅H₅)₂Ln (OC₁₄H₁₃NO) (Ln=Sm (1), Er (2), Dy (3), Y (4)), which have been characterized by elemental analysis and mass spectra. The X-ray determination of 1 indicates that the complex is monomeric in which the metal center is coordinatively saturated by two cyclopentadienyl rings and two oxygens and one nitrogen from the Schiff base ligand. The average Sm–C bond distance is 2.723(7) Å, while those of the metal center to the Schiff base oxygens and nitrogen atoms are 2.232(4), 2.572(4) and 2.534(4) Å, respectively.