Room Temperature Crystal Structure Research Articles

Pressure Effect on Organic Radicals

The magnetic properties of galvinoxyl (4-[3,5-bis(1,1-dimethylethyl)-4-OXO-2,5-cyclohexadiene-1-ylidenemethyl]-2,6-bis (1,1-dimethyl-ethyl)-phenoxy) and F5PNN (2-pentafluorophenyl-4,4,5,5-tetramethyl-4,5-dihydro-lH-imidazol-1-oxyl 3-oxide) under pressure are presented. We have found that the structural changes of both compounds can be suppressed by pressurization. The phase transition to a diamagnetic state of galvinoxyl can be suppressed by applied pressure. It has been found that under 7 kbar, the transition is sufficiently suppressed and the ferromagnetic interactions are preserved down to low temperature. The temperature dependence of the paramagnetic susceptibility under 7 kbar obeys the ferromagnetic chain model with 2J/kB = 25 K. The room-temperature crystal structure of F5PNN involves a uniform chain, while the low-temperature magnetism can be interpreted by the alternating antiferromagnetic chain model with 2J/K B = -5.6 K and α = 0.4. We found that under 5 kbar, the low-temperature magnetism obeys the uniform antiferromagnetic chain model with 2J/K B = -5.6 K, which is consistent with the room-temperature crystal structure.

Neutron diffraction and spin freezing in ferrates with iron in pyramidal oxygen coordination

The room temperature crystal structure of Y-0212 and La-0212 contains double layers of nearly regular (Fe, Cu)O 5 quadratic pyramides. A pecularity is the compensation of the pronounced Fe 4+ content via the introduction of additional oxygen (O(3)) in 2b. Thus a charge reservoir is created. At 10 K the materials are basically antiferromagnetic. The gradual freezing of the Fe spins is reminescent of concentrated spin glasses.

X-ray crystal structure of cytotoxic oxidized cholesterols: 7-ketocholesterol and 25-hydroxycholesterol

The cytotoxic cholesterol derivative, 7-ketocholesterol, crystallizes in a monoclinic unit cell, space group P2(1) with a = 11.405 A, b = 6.288 A, c = 35.393 A and beta = 92.75 degrees (Z = 4). Its room temperature crystal structure was solved by direct methods, i.e., the minimal principle via the Shake-and-Bake (SnB) algorithm. In contrast to the continuous chain pattern found for the cholesterol monohydrate structure, hydrogen bonding in the 7-ketocholesterol structure is localized to specific sites via one water molecule that forms linkages between two O3 hydroxyl groups and one keto oxygen. The final weighted R factor for 4562 reflections was 0.144. The 25-hydroxycholesterol also crystallizes in a monoclinic unit cell (P2(1)), with a = 10.840 A, b = 14.533 A, c = 16.093 A and beta = 95.91 degrees (Z = 4). The low temperature structure was solved by DIRDIF. In this instance, molecular packing is anti-parallel in layers stabilized by hydrogen bonding networks via both hydroxyl functions, differing both from cholesterol monohydrate and the 7-ketocholesterol. The final weighted R-factor for 6566 reflections was 0.034. Functional differences of the oxysterols therefore, may be expressed by observed variations in the molecular packing and geometry.

Re-examination of the room temperature crystal structure of by x-ray diffraction experiments: observation of new superlattice reflections

A recent electron paramagnetic resonance (EPR) study of revealed the existence of an antisymmetric exchange interaction, , between Cu spins on the c-axis in this compound (Yamada I, Nishi M and Akimitsu J 1996 J. Phys.: Condens. Matter 8 2625). To allow this interaction, the crystal structure must have no inversion centre halfway between relevant Cu sites. However, the structure with the space group Pbmm , which was proposed for this compound by Völlenkle et al and has been accepted so far, does not allow this interaction because it has an inversion centre at the midpoint between nearest-neighbour Cu sites on the c-axis. This conflict was pointed out in the EPR study and was taken to indicate the inconsistency of the structure with Pbmm. To find the correct crystal structure of , x-ray diffraction experiments are performed at room temperature on samples which are markedly improved in their quality because they are produced by the annealing and slow cooling of single crystals grown by the floating-zone method. As a result, new superlattice reflections which had not been reported so far are detected. The space group and the unit cell are determined to be and , respectively, where is the pseudo-unit cell proposed by Völlenkle et al. The newly found structure allows the antisymmetric interaction mentioned above. Possible connections between the new structure and the question of why the structural transition, which brings about the dimerization of Cu spins, occurs in are discussed.

Lewis-Base Adducts of Group 11 Metal(I) Compounds. LXIV Syntheses, Spectroscopy and Structures of Some 1 : 4 Adducts of Copper(I) and Silver(I) Perchlorates with Triphenylarsine and Triphenylstibine

Syntheses and room-temperature single crystal X-ray structure determinations are recorded for adducts [M(EPh3)4] (ClO4), M = Cu, E = As (1), Sb (2); M = Ag, E = As (3), Sb (4), enabling comparison with analogous, previously studied MP4 and MN4 environments. The four complexes so characterized all crystallize in the familiar rhombohedral R-3 array (a ≈ 14·4, c ≈ 52 Å, hexagonal setting) with the metal and chlorine atoms located on crystallographic threefold axes. In these arrays Cu–E (axial, off axis) are 2·493(2), 2·533(1) for (1), and 2·572(1), 2·577(1) Å for (2), the disparity in the two independent M-E distances being diminished relative to those of previously studied phosphorus analogues, perhaps in consequence of increasing E size. In (3) and (4), some cation disorder is evident in respect of the ligand pnictide atom (E); for the major components Ag-E are 2·652(3), 2·680(2) in (3); 2·732(2), 2·7295(8) Å in (4). Problems associated in defining the metal atom environment geometries in the latter are, nevertheless, more satisfactorily overcome in two further determinations of nitrate salts: [Ag(SbPh3)4] (NO3) (5) is of the rhombohedral family with no cation core disorder, Ag–E (axial, off axis) being 2·720(4), 2·725(2) Å, while the structural characterization of a 1 : 4 triphenylarsine adduct of silver nitrate is recorded as its tetraethanol solvate, namely [Ag(AsPh3)4] (NO3).~ 4C2H5OH(6), monoclinic, C2/c, a 18·373(4), b 20·786(5), c 21·070(8) Å, β 108·18(3)°, Z = 4 f.u. The silver atom of the [Ag(AsPh3)4]+cation unusually lies on a crystallographic 2 (rather than a 3 ) axis of the incipiently23 (T) array, with Ag-As 2·649(2), 2·650(2) Å and As-Ag-As ranging from 108·22(4) to 111·41(6)°. The structure determination of a chloroform solvate of (2), denoted (2a), of low precision, is noted, together with the structure of an interesting artefact, isomorphous with the rhombohedral oxoanion array, modelled as [Ag(PPh3)4]2 (SiF6).py (7). Bands in the far-infrared spectra of [M(AsPh3)4] (ClO4) are assigned to v(MAs) vibrations at 119 (M = Cu) and 103 cm¯1 (M = Ag); this produces a more consistent picture of the variation in the wavenumbers of the v(ME) modes in [M(EPh3)4]+ compounds than was available previously.

A high resolution, inelastic neutron scattering investigation of tunnelling methyl groups in aspirin

The tunnel frequency of protonated methyl groups in aspirin has been measured, by inelastic neutron scattering, at 2 K, to be 1.22 μeV. This result and the temperature dependence up to 42 K are in poor agreement with NMR measurements of deuterated methyl groups which conclude that the rotational potential is purely three-fold symmetric. The discrepancy is attributed to a six-fold contribution in the rotational potential for which justification is provided by a calculation of the rotational potential based on the room temperature crystal structure.

Transition metal complexes of singly and doubly deprotonated 2-thiooxamic acid

The new monomeric complexes trans-[M(HL) 2(H 2O) 2] (M = Mn, Co, Ni, Cd), trans-[M(HL) 2] · H 2O (M = Pd, Pt) and [Hg(HL) 2] have been prepared together with the polymeric compounds trans-[ML(H 2O)] n (M = Co, Ni, Zn) and trans-[PdL] n· 0.5nH 2O (HL - and L 2- = the monoanion and dianion of 2-thiooxamic acid, respectively). The X-ray crystal structures of the manganese(II) and cadmium(II) complexes of HL - show a centrosymmetric octahedral geometry around the metal ion in both molecules. The ligand HL - behaves as a bidentate chelate with ligated atoms being the thioamide sulfur and one of the carboxylate oxygens. The room-temperature crystal structure of the known cis-[Zn(HL) 2(H 2O)] complex has also been determined and is compared with the previously published structure at 120 K. The complexes were characterized by elemental analyses, conductivity measurements, X-ray powder patterns, magnetic susceptibilities and spectroscopic (IR, far-IR, Raman, UV-vis) studies. The vibrational analysis of the complexes is given using OH/OD, NH/ND and metal isotopic substitutions. All data are discussed in terms of the nature of bonding and known and assigned structures. The dianion L 2− acts as a bis-bidentate O,N/O,S bridging ligand yielding square-planar (Pd II) and octahedral (Co II, Ni II, Zn II) polymeric compounds.

Comparison of the Geometries of 3,7,10-Tribenzyl-3,7,10-triaza[3.3.3]propellane, (1), 7,10-Dibenzyl-3-p-tolyl-3,7,10-triaza[3.3.3]propellane, (2), and 7,10-Dibenzyl-3-oxa-7,10-diaza[3.3.3]propellane, (3)

Room-temperature crystal structures are reported for three analogous [3.3.3]propellanes. Compound (1), C29H33N3, is trigonal, (2), C29H33N3, triclinic and (3), C22H26N2O, orthorhombic. All three molecules have eclipsed conformations about the central conjoining bond, and the five-membered rings all have envelope conformations (Cs-m symmetry).

Chain-Folded Lamellar Crystals of Aliphatic Polyamides. Comparisons between Nylons 4 4, 6 4, 8 4, 10 4, and 12 4

Chain-folded single crystals of the five even−even nylons 4 4, 6 4, 8 4, 10 4, and 12 4 were grown from solution and their structures and morphologies studied using transmission electron microscopy, both imaging and diffraction. Sedimented mats were examined using X-ray diffraction. All these nylons have room temperature crystal structures that relate to that reported for nylon 6 6, yet there are differences, reflecting the differences in the amide group distribution. At room temperature, all the crystals are composed of chain-folded, hydrogen-bonded sheets; the hydrogen bonds within the sheets form a progressive shear pattern, and, in addition, the sheets themselves are sheared progressively parallel to the sheet plane so that they generate triclinic unit cells. The magnitude of this intersheet shear may differ between nylons; it is dependent on the details of the amide decoration pattern on the hydrogen-bonded sheet faces. In all five nylons studied, the two strong and characteristic diffraction signals...

Constrained Rietveld refinement of [β-1H1]decadeuteriodopamine deuteriobromide using powder neutron diffraction data

The room-temperature crystal structure of [β-1H1]decadeuteriodopamine deuteriobromide has been refined using pulsed neutron diffraction data collected from a powder sample. A Rietveld refinement involving 93 structural parameters converged to give a χ2 of 1.99 for the fit, with 5366 observations and 111 basic variables. The agreement factors Rwp= 2.47%, Rp= 2.74%, RI= 5.70% and RE= 1.75% indicate an excellent fit to the data. Slack chemical constraints were used in the refinement to impose prior chemical sense on the final structure. The dopamine cation is extensively hydrogen bonded to bromide ions, and the hydrogen-bond geometries are well defined.

Synthesis of nanophase ZnO, Eu2O3, and ZrO2 by gas-phase condensation with cw-CO2 laser heating

Abstract This Letter describes cw-CO 2 laser vaporization and gas-phase condensation of nanophase ZnO, Eu 2 O 3 and ZrO 2 (particle diameters range from 5–280 nm, 2–30 nm, and 1–13 nm, respectively). ZnO forms in the usual room-temperature crystal structure but Eu 2 O 3 crystallizes in a metastable monoclinic phase.

Low-temperature crystal and band electronic structure of organic metals, α- (BETS)2I3 and (MeBr-DCNQI)2Cu

Abstract Room temperature and low-temperature(13K) crystal and band electronic structures of α- (BETS)2I3 (BETS=bis(ethylenedithio)tetraselenafulvalene) were examined by using a newly developed X-ray crystal structure analysis system based on imaging plate(IP) equipped with a closed-cycle helium refrigerator. The X-ray low-temperature studies of (MeBr-DCNQI)2Cu (DCNQI=dicyanoquinonediimine) by using IP system have revealed that the structure change mainly associated with the charge ordering of Cu occurs discontinuously at TMI but the structure change related to the development of CDW on DCNQI stacks is continuous.

The crystal structures of some doped and undoped alkaline earth cerate perovskites

The room-temperature crystal structures of undoped and doped barium and strontium cerate perovskite have been refined from medium-resolution, neutron time-of-flight powder diffraction data. The compounds BaCeO 3, SrCeO 3, BaCe 0.85Pr 0.15O 3 and SrCe 0.95Yb 0.05O 2.975 all crystallise in the orthorhombic space group Pmcn with the GdFeO 3 structure type. The crystal structure of SrCeO 3 was solved from high-resolution neutron powder data by determining the magnitudes of the octahedron tilt angles from the psuedocubic lattice constants, and then refining the two structural alternatives using the Rietveld method to determine the correct structure. The structures of both doped samples are only slightly different from those of the undoped ones, reflecting the good lattice match of these ions for Ce 4+. The extrinsic anion vacancy could not be located unambiguously in SrCe 0.95Yb 0.05O 2.975 and was found to be absent in BaCe 0.85Pr 0.15O 3 in keeping with the expected stoichiometry. This contrasts with BaCe 0.9Y 0.1O 2.95 where the vacancy was located on O2.

Characterisation of the Fermi surface and phase transitions of (BEDO-TTF)2 ReO4�(H2O) by physical property measurements and electronic band structure calculations

The electronic properties of the organic superconductor (BEDO-TTF)2 ReO4·(H2O) were investigated by temperature dependent resistivity, ESR, Hall effect and magnetoresistance measurements. Shubnikov-de Haas (SdH) oscillations were observed in magnetic fields up to 24 T in the temperature range 0.5 K to 4.2 K. The electronic band structure of (BEDO-TTF)2 ReO4·(H2O) was calculated by employing the extended Hückel tight binding method on the basis of its room temperature crystal structure. The two observed SdH frequencies of 75 T and 37 T correspond very well with two cross-sectional areas of the hole and electron Fermi surface pockets obtained from the tight binding calculation. From the temperature dependence of the SdH oscillation amplitudes, the cyclotron effective mass (mc) belonging to the larger and smaller pockets were found to be 0.9 m0 and mc=1.15 m0 respectively. Measurements of the angular dependence of the SdH frequencies show no deviation from that expected for a cylindrical Fermi surface. In terms of our tight binding calculations and experimental measurements, probable causes for the 213 K and ∼35 K phase transitions are discussed. The calculations show that (BEDO-TTF)2 ReO4·(H2O) is a two dimensional semimetal but possesses a hidden nesting. The latter is likely to cause an SDW instability leading to the ∼35 K transition. The resistivity drop associated with the 213 K transition is likely to be induced by an abrupt increase in the relaxation time. The excellent agreement between the calculated and experimentally observed Fermi surface implies that, with decreasing temperature below 35 K, (BEDO-TTF)2 ReO4·(H2O) gradually gets out of the SDW state and re-enters the “original” metallic state, in which it becomes superconducting below 2.4 K.

Facial tris cyclometalated rhodium(3+) and iridium(3+) complexes: their synthesis, structure, and optical spectroscopic properties

The synthesis of the facial tris cyclometalated complexes fac-[Rh(ppy) 3 ] (ppyH=2-phenylpyridine), fac-[Ir-(ppy) 3 ], and fac-[Ir(thpy) 3 ] (thpyH=2-(2-thienyl)pyridine) by a generalized method is described. The conformation of the complexes is discussed on the basis of the 1 H NMR spectra, and for fac-[Ir(thpy) 3 ] the room-temperature crystal structure is presented: chemical formula C 27 H 18 N 3 S 3 Ir, cubic, space group Pa3, Z=8, a=16.872(4) A, V=4803(3) A 3 . The excited-state properties are investigated by absorption, luminescence, and luminescence line-narrowing spectroscopy in different media

Structural Chemistry of Some Phases in The YC-Ni-B System

ABSTRACTNiB, monoclinic Ni4B3, Ni2B and Ni3B were prepared by arc-melting and their roomtemperature crystal structures were refined by Rietveld analysis of neutron powder diffraction data. The NiB refinement is altogether new data. Although the B atoms in NiB form characteristic zigzag chains, the primary coordination of each atom by atoms of the other kind is similar and distinctively sevenfold, with one short (2.117 Å), two intermediate (2.152 Å), and four long (2.163 Å) bonds. Other samples with stoichiometries (YC)nNi2B2, n = 3, 4, did not yield single-phase material, but both x-ray and neutron powder diffraction suggest that the n = 4 structure is present in both of these samples. Phase-pure samples of these homologues may require non-stoichiometry and a more controlled thermal history than is attainable by arc melting.

New host architecture of hydroquinone with enclathrated C70

The room-temperature crystal structure of a molecular 1:4.5:1 complex of C[sub 70], hydroquinone (HQ), and benzene (bz), C[sub 70](HQ)[sub 4.5]bz, is reported. The solid-state architecture of the donor-acceptor complex has trigonal symmetry and consists of a novel H-bonded superoctahedral HQ host network with three different types of cavities enclathrating the C[sub 70] and bz guest molecules. Giant HQ twin cages shaped according to the shell of a peanut house a pair of C[sub 70] molecules, large single cages accommodate one C[sub 70] guest, and smaller HQ cages of tetrahedral shape embrace a sandwich pair of bz molecules. The long axes of the C[sub 70] guest molecules are orthogonal to the trigonal crystal and cage axes. Their HQ host cages may be viewed as expanded supercubes and related to the simple supercube cavities of the sister complex C[sub 60](HQ)[sub 3] reported previously. A topological analogy exists between the tetrahedral HQ cages and the supertetrahedral building blocks of the pyrochlore network. The HQ host network of C[sub 70](HQ)[sub 4.5]bz is essentially ordered, and the C[sub 70] and bz guest species are orientationally disordered. The adopted benzene guest model is provisional only and requires further backing. 8 refs., 4 figs., 1 tab.

Structural features of homo- and heteroleptic complexes of copper(II) with 2,2,6,6-tetramethyl-3,5-heptanedione and 3-chloro-2,4-pentanedione

The crystal structure of bis(2,2,6,6-tetramethyl-3,5-heptanedionato) copper, Cu(thd) 2, has been determined at 130, 250 and 293 K (monoclinic, space group P2 1/ c, a = 10.200(3), b = 10.957(3), c = 11.491(4) Å, β = 112.05(2)° at 130 K). At 130 K the structure shows no disorder. One of the t-Bu groups is involved in an unusually short intermolecular contact. At higher temperatures this same group is disordered. The number of configurations increases with the temperature. The room temperature crystal structures of bis(3-chloro-2,4-pentanedionato)copper, Cu(Clacac) 2 (monoclinic, space group P2 1/ n, a = 4.815(2), b = 17.107(3), c = 8.013(2) Å, β = 106.92(2)°), and (2,2,6,6- tetramethyl-3,5-heptanedionato)(3-chloro-2,4-pentanedionato) copper, Cu(thd)(Clacac) (orthorhombic, space group Pnma, a = 19.213(4), b = 6.453(4), c = 15.725(4) Å) are also described. Two kinds of molecular stacking are observed depending on whether the complex is homo- or heteroleptic.

Crystal structures, phase transitions and energy calculations of poly( p-phenylene) oligomers

The room temperature crystal structures, unit cell dimensions at 110K and phase transitions of three poly( p-phenylene) oligomers are reported. The structures of p-quinquephenyl (PQP), C 30H 22, p-sexiphenyl (PSP), C 36H 26, and p-septiphenyl (PSeptiP), C 42H 30, each belonging to space group P2 1/c, are similar to those of shorter oligomers. The unit cell dimensions are a = 22.056 Å, b = 5.581 Å, c = 8.070 Å and β = 97.91° for PQP, a = 26.241 Å, b = 5.568 Å, c = 8.091 Å and β = 98.17 ° for PSP, and a = 30.577 Å, b = 5.547 Å, c = 8.034 Å and β = 100.52 ° for PSeptiP. The a axis increases with molecular length. The molecules are linear and planar in all three structures. The herringbone nature of the packing is similar for PQP and PSeptiP, while a considerably greater tilt occurs in PSP. At 110K, the unit cell parameters b and c are approximately doubled while a remains nearly the same as in the room temperature cell. A time-dependent solid state transition is observed for PQP, PSP and PSeptiP when crystals are cooled to 110K. At elevated temperatures, thermal measurements indicate the oligomers to be thermotropic liquid crystals. The crystal-smectic transition temperatures are reported for PQP, PSP, PSeptiP and p-octiphenyl (POP), C 48H 34. The results of a molecular mechanics study on the conformation and packing of PSP are also presented. The competition between intramolecular forces (such as ortho hydrogen repulsions) and intermolecular crystal packing forces was examined in particular. Molecular mechanics calculations predict non-planar conformations in isolated polyphenyls, implying that conjugation between phenyl rings is insufficient to overcome ortho hydrogen repulsions. In a crystalline environment, however, intermolecular forces tend to force a planar conformation. Calculations on arrays of PSP molecules show that changing the phenyl-phenyl torsion angles from the coplanar value increases the total energy of the structure. The most favourable intermolecular interactions between oligomers are achieved for conformations having the phenyl rings coplanar.

ESR study in (BEDT-TTF)3Li0.5Hg(SCN)4(H2O)2

ESR (Electron Spin Resonance) in (BEDT-TTF)3Li0.5Hg(SCN)4(H2O)2 (abbreviated as Li salt) has been measured down to liquid He temperature. The ESR studies for α-(BEDT-TTF)2 XHg(SCN)4 (X=K and Rb) salts which have suggested the coexistence of metallic state with a magnetic ordered state [1] have stimulated this work. We studied Li salt to study whether the M-I transition is magnetic or not. In the insulating state, we have seen two pairs of sharp peaks with strong and weak intensities. Our X-ray analysis shows no twinning effect. We analyzed the g-value data for the stronger pair, and got the principal g-values consistent with the localized hole on the BEDT-TTF molecules. We cannot expect two kinds of signals from the room temperature crystal structure. One of the possible origin of the two strong pairs of resonance is due to the carriers localized at the ends of the BEDT-TTF molecules.