Structural Studies of 1:1 Quinone-Hydroquinone Complexes

The structures of the 1:1 quinone-hydroquinone complexes of 2-phenyl and of 2-(4′-chloro) phenylbenzoquinone have been studied by X-ray methods. A superficial study would indicate that the quinhydrones are centrosymmetric and belong to the space group P2₁/c. However, other evidence indicates that the true crystal structure may belong to either the space group P2₁ or to Pc, or that the crystal may contain regions that would coresspond to each of these two non-centrosymmetric space groups. Some possible consequences of such a structural arrangement are briefly discussed.     

Non-crystallographic symmetries in the superstructure of (NH4)2ZnCl4

The modulation vector turned out to be equal 1/4. The lattice constants of the orthorhombic superstructure are determined: a = 12.6197(16) Å, b = 7.2107(81) Å, c = 4 × 9.2746(15) Å. The two of the four absences rules are interpreted as corresponding to the non-crystallographic symmetries: The space group P 2₁cn is determined on the basis of the single crystal X-ray pictures taking into account the experimental evidence of pyroelectricity in (NH₄)₂ZnCl₄.     

Crystal structure and physical characterization of <Emphasis Type="Italic">N</Emphasis>-(3,3-dimethylbutyl)-<Emphasis Type="SmallCaps">l</Emphasis>-α-aspartyl-<Emphasis Type="SmallCaps">l</Emphasis>-phenylalanine,the hydrolysis product of neotame

The hydrolysis product of neotame, N-(3,3-dimethylbutyl)-l--aspartyl-l-phenylalanine (DMBAP), was crystallized from water as an anhydrate with a melting point at 197C with decomposition. Its crystal structure was determined by single crystal X-ray diffractometry. The crystal is orthorhombic with space group P2₁2_₁2₁ with Z=4 and one molecule per asymmetric unit. The cell constants are a=5.520 (2) Å, $b=10.608$ (5) Å and c= 31.92 (2) Å. The ¹³C solid-state nuclear magnetic resonance spectrum of DMBAP is compared with those of neotame monohydrate and neotame methanol solvate.     

Crystal- and molecular structure of 19-nor-digitoxigenin

19-nor-Digitoxigenin crystallizes in the orthorhombic space group P 2₁2₁2₁ with four formula units C₂₂H₃₂O₄ per unit cell. The lattice parameters are a = 7.082, b = 12.476, c = 21.486 Å. The crystal structure was determined by direct methods and refined by a least-squares procedure to the discrepancy factor R = 0.042. — The orientation of the lactone ring relative to the steroid skeleton was found to be the opposite of that known for digitoxigenin.     

Structure and nonlinear optical properties of the family of lead and barium nonaborates with a zeolite-like framework

The structures of new nonaborates, (Pb,Ba)₃(OH)[B₉O₁₆][B(OH)₃] (space group P31c) and Ba₃Na(OH)[B₉O₁₆][B(OH)₄] (space group P1), synthesized under hydrothermal conditions, have been investigated. These structures differ from the structure of the previously studied nonaborate Pb₃(OH)[B₉O₁₆][B(OH)₃] (space group P31c) in the occupation of the zeolite nonaframework, which, in the case of the (Ba,Na) borate, contains a larger number of cations and OH groups. Despite this difference, all the structures have a high trigonal or pseudotrigonal symmetry, which suggests the existence of the structure type or the family of nonaborates. The structural similarity is violated by the presence of B(OH)₄¹⁻ tetrahedra instead of neutral trigonal groups B(OH)₃ in channels of the (Ba,Na) borate. The latter polyhedra are characterized by a pseudomonoclinic arrangement that corresponds to the space group Cc with the true triclinic group P1. The ability of nonaborates to generate the optical second harmonic as a function of the specific features of their crystal structures is discussed.     

Crystal and molecular structure of 7-hydroxyflavone monohydrate, C14H10O3·H2O

The X-ray crystal structure of 7-hydroxyflavone monohydrate, C₁₄H₁₀O₃ · H₂O, is determined. The compound crystallizes in the monoclinic space group, P2₁/n with a = 3.801(3), b = 19.665(4), c = 16. 039(6), = 93.69(3)°, and = 0.68 mm^–1 for Z = 4. The phenyl ring of the flavone moiety is rotated 18.6(1)° out of the penzopyran plane, which is a typical value for flavones. In the crystal lattice, there are wide channels which are lined mainly by C–H groups. The water molecules enclosed in these channels are severely disordered.     

The P\bar 1 space group changes in journal of crystallographic and spectroscopic research and in journal of chemical crystallography

The crystal structures of seven compounds, originally described in the centrosymmetric triclinic space group (No. 2), have been revised to centered monoclinic. Six are now described in space group No. 15 (C2/c or I2/a) and one in space group No. 12 (C2/m). Three structures (TADTEX, VICHIY, YAWZUR) have been re-refined in the correct space group. For six instances the decrease in symmetry results in only minor adjustments and the structure is essentially correct as it is expected when the original and the revised space groups are both centrosymmetric. However, in one instance (VICHIY) the reformulation in the higher space group changes (unexpectedly) the molecular dimension as much as 0.12 Å, even if the space group change is between two centrosymmetric space groups (from to C2/c). This was attributed to the easy decomposition of the crystal. The percentage of revised crystal structures was found to be 1.71%, namely 8 on a total of 467 analyzed structures. A low value if compared to the 3% value found by Marsh and Spek for C2 space group.     

Polymeric metal‐organic octupolar NLO materials: lithium(I) and sodium(I) 3,5‐dinitrobenzoates

Lithium 3,5‐dinitrobenzoate (Li(dnb)) exhibits a 1D propeller chain structure of D ₃ point symmetry and the chains are trigonally assembled in the crystal under the chiral space group P 3₁21. Sodium 3,5‐dinitrobenzoate (Na(dnb)) also crystallizes in space group P 3₁21 and exhibits a 3D structure. The structure of Na(dnb) could be regarded to be similar to that of Li(dnb) if the weaker Na‐O(nitro) bonds were to be ignored. These two compounds represent rare examples of octupoles arranged in an octupolar environment and show modest powder SHG effects. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal and molecular structure of a steroidal spirocyclic lactone, C29H34O4

The X-ray crystal structure of the title compound, as crystallized from methanol–methylene chloride was determined. The asymmetric unit contains two steroid molecules, which differ primarily in the orientation of the aromatic rings of the benzyl ethers. The title compound crystallizes in the noncentrosymmetric space group P2(1), with a = 7.558(2), b = 16.673(3), c = 18.735(4) Å, = 97.610(10)°, and D _calc = 1.268 g cm^–1 for Z = 4.     

The crystal structure analysis of iron nitroprusside,Fe[Fe(CN)5NO]·3H2O

The crystal structure of iron(II) pentacyanonitrosylferrate trihydrate has been determined from three dimensional, single-crystal X-ray diffraction data. Fe[Fe(CN)₅NO]·3H₂O crystallizes in the monoclinic space group P2₁/n with lattice constants,a=7.205(1),b=14.641(2),c=10.680(1) Å,=91.14(1)° andZ=4,D _m =1.89(1) g cm^–3 andD _x =1.92 g cm^–3. Final full-matrix least-squares refinement of 1691 unique reflections yieldedR=0.024 andR _w =0.028. Both iron atomic centers have distorted octahedral symmetries. The cation iron center is coordinated by five cyanide ligands and one water molecule, while the second iron center is coordinated by five cyanide ligands and one nitrosyl group. Cyanide bridging links the metal centers. Two uncoordinated water molecules, O(2) and O(3), are hydrogen bonded to the coordinated water molecule, O(1), and occupy channels in the crystal lattice. Important mean bond distances for iron nitroprusside are: Fe(cation)-N=2.159(17), Fe-C=1.936(4) and C=N=1.144(6) Å. Other notable bond lengths include: Fe-O(1)=2.152(2), Fe-NO=1.669(2) and NO=1.131(3) Å. The distances between the coordinated water molecule and two uncoordinated water molecules are 2.855(3) and 2.740(3) Å.     

Crystal Structure of an Adduct of Sarcosine with Sulfuric Acid (at 140 K)

The crystal structure of an adduct of sarcosine with sulfuric acid, (C₃NO₂H₈)₂SO²⁻₄, has been determined at low temperature (140 K). The crystals are triclinic, space group = P1 with the unit cell dimensions, a= 7.623(1) Å, b = 11.538(2) Å, c = 14.214(2) Å, α = 71.46(2)°, β = 74.36(2)°, γ = 86.46(2)°. Based on 4924 reflections with intensities larger than 3σ(I), the structure was refined to a conventional R factor of 0.038 giving e.s.d.s. in bond lengths and angles of 0.003 Å and 0.2°, respectively. There are two formula units in the asymmetric unit and both sulfate ions exist in two disordered orientations. The sulfate group 1 occupies the two orientations in the proportion 0.82/0.18 and sulfate group 2 in proportion 0.69/0.31. Both Orientations of the sulfate groups satisfy the hydrogen bonding scheme equally well. There is also a pseudo-symmetry element within the asymmetric unit as one half of this unit is transformcd into the other by a translation of approximately one half along the b- and c-axes. Thus, sarcosine molecule 1 is translated to sarcosine IV and sarcosine II to III. In the same manner, the sulfate group I in its main orientation is translated to the sulfate group 2 in its alternative orientation and vice versa.     

Crystal and molecular structure of o-methacryloylaminophenylarsonic acid

The title compound, o-methacryloylaminophenylarsonic acid (o-MAPHA), C₁₀H₁₂AsNO₄, is a monomer used to obtain water-soluble polyelectrolytes. It was obtained from the condensation reaction of o-arsanilic acid and methacryloyl chloride. Crystallization from aqueous ethanol solution yielded colorless prismatic crystals, and one was used for X-ray analysis. The crystal structure was solved using direct methods with a refined R ₁ = 0.0483. The crystal structure belongs to the triclinic system, space group , and the asymmetric unit comprises two molecules of the o-MAPHA acid and one water molecule. Both acid molecules are approximately planar and in both molecules the As atom presents common tetrahedral geometry with two long As–O bonds for hydroxyl groups and one short As–O bond for the oxo groups. The structure of o-arsanilic acid (o-ARSA), C₆H₈AsNO₃, was also determinated using the same methods and compared with the o-arsanilic acid structure previously reported. The crystal structure of the o-arsanilic acid belongs to the monoclinic crystal system and to the P2₁ noncentrosymmetric space group with Z equals two.     

Synthesis and crystal structure of [Y(NO3)3(OH2)3]·(Me2-16-crown-5)·H2O

The complex [Y(NO₃)₃(OH₂)₃]·(Me₂-16-crown-5)·H₂O has been prepared and its crystal and molecular structure determined using single crystal X-ray diffraction. The colorless crystals belong to the monoclinic space group P2₁/n with Z = 4. Lattice parameters are a = 10.420(1), b = 17.257(3), c = 14.646(2) Å, = 96.79(1)°, V = 2615.1(6) ų. The yttrium(III) ion is nine-coordinate, bonded to three bidentate nitrate groups and three water molecules. The average Y–O(nitrate) and Y–O(water) distances are 2.42(3) and 2.33(1) Å, respectively. The average HO–H···O hydrogen bonded separation is 2.767Å.     

Synthesis and X-ray structure of 5′-methoxy-2,4,6-trimethyl-2′-nitrosobiphenyl

The synthesis and X-ray crystal structure of 5-methoxy-2,4,6-trimethyl-2-nitrosobiphenyl is reported. The compound (C₁₆H₁₇NO₂) is monoclinic, with a = 11.080(4), b = 16.899(6), c = 15.410(5) Å, = 108.329(5)°, and space group P2₁/n. There are two independent molecules within the crystal. In each of these molecules the two phenyl rings are mutually orthogonal, with interplanar dihedral angles of 85.09 and 89.43° respectively. The nitroso substituents are essentially coplanar with the phenyl ring, with torsional angles of only 3.5 and 2.2°, respectively, while the methoxy groups make angles of 5.2 and 10.0°, respectively, with the phenyl ring.     

The crystal structure of UO2Cl2(OH2)(MeCN)2·2MeCN

The crystal structure of UO₂Cl₂(OH₂)(MeCN)₂·2MeCN has been determined at 123 K. The crystal is orthorhombic, space group Pnma, witha=14.891(8),b=6.733(6),c=15.931(9) Å, andD _calc=2.18 g cm^–3 forZ=4. The finalR value for 951 unique observed [F ₀5(F ₀)] reflections is 0.064. The U atom is seven-coordinate, pentagonal bipyramidal. The two axial positions are occupied by the uranyl oxygen atoms. Within the equatorial plane lie two acetonitrile groups, two chlorine atoms and a water molecule, the latter positioned between the two chlorine atoms. All of the atoms except the uranyl oxygen atoms lie in crystallographic mirror planes. The water molecule is hydrogen bonded to the two uncoordinated solvent molecules. Several close contacts between the solvent methyl groups and chlorine atoms suggest weak C-H acidic interactions of the type C-HCl.     

Crystal and molecular structure of [H3O·18-crown-6]2-[ReCl6] isolated from a liquid clathrate medium

The crystal and molecular structure of [H₃O·18-crown-6]₂[ReCl₆]1 is reported. Crystal data for1: trigonal, space group R ,a=13.857(2) Å,c=10.154(2) Å,D _c =2.85 g/cm³,Z=3,R _f =0.073,R _w =0.064. The oxonium ion is observed to be crystallographically disordered lying 0.37 Å on both sides of the plane defined by the crown ether oxygen atoms. The anion resides on a crystallographic position forming a slightly distorted octahedron.     

Quench Hardness Anisotropy of Rhombohedral Crystals: Calcite

Variation of microhardness with orientation of indenter (A) and quenching temperature T_q is studied on freshly cleaved surfaces {100} of natural rhombohedral crystals of calcite by producing Knoop indentations for various applied loads. The relation between hardness H_A and quenching temperatures for the high loads (40–80 g) is graphically established. It also depends on the crystal orientation. The anisotropic indices are also determined.     

PM3 semiempirical study and its comparison with X-ray crystal structure of 4-[2-Methyl-4-(4-methoxyphenylazo)] phenoxyphtalonitrile

  The molecular and crystal structures of the title compound, C₂₂H₁₆N₄O₂, were determined by single crystal X-ray diffraction technique. The title compound crystallizes in monoclinic space group P1 2 ₁ /n1, with a=12.7811(9) ?, b=8.2002(4) ?, c=17.8772(14) ?, Z=4, D _calc=1.3112(1) g/cm³, μ (Mo-K_α)=0.087 mm⁻¹. The structure was solved by direct methods and refined to a final R=0.056 for 1891 reflections with I > 2σ (I). The asymmetric unit in the crystal structure contains only one neutral molecule. The positions of nitrogen atoms in the azo groups were disordered. There is no classic hydrogen bond in the crystal structure. The molecules in the crystal structure are stacked by π–π stacking and one edge-to-face interactions. In order to determine conformational flexibility and crystal packing effects on the molecules, molecular energy profile of the title compound was obtained with respect to the selected torsion angle, which is varied from −180° to +180° in every 10° via PM3 semi-empirical method.     

The emission and structure of a new laser crystal Nd3+: NaY(WO4)2

A new laser Nd³⁺ : NaY(WO₄)₂ crystal rod of Φ 2.5 × 5 mm was pumped by a xenon flash lamp, and a 1.06 μm laser output was for the first time obtained in our laboratory, which has a threshold lower than 1 J. The crystal structure of NaY(WO₄)₂ was determined. The crystal is tetragonal, with the space group 14₁/a, a = 5.205(2) Å, c = 11.251(3) Å, V = 304.8(2) ų, Z = 2, D_calc = 6.62 g/cm³, D_obs = 6.51 g/cm³.     

Polymorphic single crystal ↔ single crystal transformations in Rb0.975Cs0.025NO3

The crystal growth morphology of modifications IV, III, II, and I during the IV ↔ III ↔ II ↔ I polymorphic transformations in Rb_0.975Cs_0.025NO₃ has been investigated by optical microscopy. The equilibrium temperatures between phases IV and III (T ₀ = 393 ± 0.5 K), III and II (T ₀ = 421 ± 0.5 K), and II and I (T ₀ = 497 ± 0.5 K) of the crystal studied have been determined. It is established that these transformations are of the single crystal ↔ single crystal type and occur with the formation and growth of new-crystal nuclei in crystalline matrices.