Synthesis, X-ray and neutron diffraction and Mössbauer studies of SrFeOx crystals

Tetragonal single crystals of the nonstoichiometric strontium ferrate with the lattice parameters a = 3.8525(3) and c = 3.8781 (3) Å have been synthesized for the first time by the method of floating-zone melting in the SrFeO_x system. The neutron diffraction patterns of the crystals showed weak additional reflections indicating the formation of the superstructure with double spacing along the [hh0] direction. The Mössbauer spectra of the crystals were obtained and measured in the temperature range 80–300 K. It was established that below the temperature T _N = 232(1) K, the crystals are in the magnetically ordered state with 3/5 of iron ions being in the trivalent state and all the remaining iron ions in the tetravalent state. This leads to the crystal composition SrFeO_2.71. The electric resistivity of the crystals equal to 100 ω cm at room temperature drastically decreases at temperatures exceeding 470 K.     

X-ray diffraction and DFT structures of the pentacyanocarbonylferrate(3—) ion

Recently (Soria, D.B.; Aymonino, P.J. Spectrochim. Acta 1999, A55, 1243), we reported improved ¹³C NMR and IR and Raman spectra, as well as the TGA-DTA behavior of Na₃[Fe(CN)₅CO]·2H₂O. We now report for the first time the structure of the anion obtained by x-ray diffraction (XRD) measurements performed with single crystals of the mixed Na₁₆{[Fe(CN)₅CO]₄[Fe(CN)₆]}··32H₂O salt which crystallizes in the tetragonal I4/m space group, with a = 16.308(2), c = 15.418(2) Å, and Z = 2. The theoretical structure and the wave numbers corresponding to the normal modes of vibration of the [Fe(CN)₅CO]^3? (carbonylprusside) anion were calculated with DFT methods and compared with experimental results.     

X-ray mapping in heterocyclic design: 17. Crystal and molecular structures of the “molecule of the month”; and its hydrogenated form

The structures of 2,8-dimethyl-5-[2-(6-methylpyridin-3-yl)ethyl]-2,3,4,4a,5,9b-hexahydro1H-pyrido[4,3-b]indole trihydrobromide (I) (a = 12.865(4) ?, b = 14.281(3) ?, c = 13.553(3) ?, Z = 4, sp. gr. Pna2₁) and 2,8-dimethyl-5-[2-(6-methylpyridin-3-yl)ethyl]-2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole dihydrobromide (II) (a = 13.9704(14) ?, b = 14.4447(15) ?, c = 10.7819(12)?, β = 107.58(1)°, Z = 4, sp. gr. P2₁/c) were studied by single-crystal X-ray diffraction. The structures were solved by direct methods and refined by the full-matrix least-squares method with anisotropic displacement parameters to the R factors of 0.0603 and 0.0446, respectively. All Br⁻ anions form hydrogen bonds with protonated nitrogen atoms. The synthesis and physicochemical parameters of these two compounds are reported.     

Morphology prediction of crystals grown in the presence of impurities and solvents — An evaluation of the state of the art

Computational methods enable to calculate relative face growth rates and crystal shape from structural information alone. Even if these models are sufficient for the calculation of the habit of a vapor grown crystal, most of them fail to correctly reproduce the habit of crystal growth from solution. In recent years, new approaches have been proposed based on the substitution of additive molecules in the crystal lattice or on the surface of the crystal. The new computer-based approaches provide a fundamental understanding of processes of crystal growth from solution. The number of methods proposed in morphology prediction is enormous. Herein, an overview of these methods and approaches is provided.     

Precision X-ray diffraction and Mössbauer studies and computer simulation of the structure and properties of malayaite CaSnOSiO<Subscript>4</Subscript>

The structure and some physical properties of malayaite CaSnOSiO₄ have been studied by the precision X-ray diffraction, Mössbauer spectroscopy, and computer simulation of the structure. The unit-cell parameters a = 7.152(2) Å, b = 8.888(2) Å, c = 6.667(2) Å, β = 113.37(2)°, V = 389.0(3) ų, and μr = 0.68 are refined on a synthetic impurity-free sample. The distribution of the deformation electron density is analyzed in the basic fragments of the crystal structure forming an anionic framework. The constructed potentials of pair and three-particle interaction reproduced quite well the elastic, dielectric, and energy characteristics and allowed us to predict their numerical values, which are in good agreement with the limited available experimental data.     

X-ray diffraction analysis on the structure of the glasses in the system PbOSiO2

The structures of PbO·SiO₂ and 2PbO·SiO₂ glasses have been analyzed by use of X-ray diffraction data and pair function method. For PbO·SiO₂ glass, a model consisting of chains of PbO₃ pyramids and silicate chains showed good agreement with the observed RDF. For 2PbO·SiO₂ glass, the present authors reported previously a model in which chains of PbO₃ pyramids are connected with SiO₄ tetrahedra, while the chromatographic analyses of silicate anions by Götz et al. and Smart et al. showed that silicate anions are distributed from monomer to polymer in the glass. We reexamined the structure of this glass referring to these results. Three representative models containing isolated SiO₄, Si₄O₁₂ rings and (SiO₃)_n chains respectively as well as PbO₃ chains were constructed and the RDFs were calculated with changing structure parameters. These three models showed satisfactory agreement with the observed data, showing that silicate anions are distributed from monomer to polymer in 2PbO·SiO₂ glass and an increase of SiO₂ content leads to polymerization of silicate anions to longer chains up to PbO·SiO₂ composition, while the chains of PbO₃ pyramids remain unchanged.     

X-ray structural and molecular mechanics investigations of cyclopentadienyl-carbonyl-triphenylphosphine-methoxyacetyl-iron (η5-C5H5)Fe(CO)(PPh3)(COCH2OMe)

The crystal and molecular structure of cyclopentadienyl-carbonyl-triphenylphosphine-methoxy-acetyl-iron (2) has been determined by X-ray. The crystals are monoclinic:P2₁/n,Z=4,=7.881(1),b=19.111(3),c=15.271(2) Å and=93.44(1)°. The structure was solved by direct methods, and refined anisotropically by full-matrix least-squares against 3419 independent reflections, givingR=0.0446. Molecular mechanics calculations reproduce satisfactorily the X-ray structure.On leave from the Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai, China.     

Crystal structure of diheterolevulosan II: α-d-Fructofuranose-β-d-fructopyranose 1,2′:2,1′ dianhydride and molecular mechanics calculations on diheterolevulosan II and IV with chair and boat conformations of the central 1,4-dioxane ring

C₁₂H₂₀O₁₀,M _r=324.28, orthorhombic,P2₁2₁2₁,a=9.4476(8),b=10.2247(8),c=13.5827(11) Å,V=1312.07(18) ų,Z=4,D _x=1.642 g cm^?3, MoKα radiation (λ=0.71073 Å)μ=1.4 cm^?1,F(000)=688,T=295 K, finalR=0.041 for 1089 reflections withI≥2.5σa(I). The molecule consists of aβ-d-fructopyranose and a α-d-fructofuranose ring which are linked by a 1,4-dioxane ring. The pyranose ring and the dioxane ring both have a chair conformation, and the furanose ring has an envelope conformation. All six hydroxyl groups act as donors in intermolecular hydrogen bonding. Each molecule is hydrogen-bonded to eight neighbor molecules by fourteen hydrogen bonds, forming a three-dimensional framework. The hydrogen bonds of varying geometry give rise to five sharp hydroxyl stretch vibrations in the infrared spectrum. In diheterolevulosan IV the central dioxane ring is a boat. Molecular mechanics calculations on diheterolevulosan II and IV having different boat and chair conformations of the dioxane ring show that the lowest energy conformations correspond to the conformations observed in the crystal structure. For comparison the calculations also have been applied to 1,4-dioxane having boat and chair conformations.     

X-ray and NMR studies on the rotational isomerism about the C(5)-C(6) bond of 6-substituted methyl 2,3,4,-tri-O-acetyl-6-X-α-D-glucopyranoside derivatives

The rotamers about the C(5)–C(6) bond of a series of 2,3,4-tri-O-acetyl-6-X--D-glucopyranozide derivatives resulting by substitution at C(6) or O(6) have been studies with¹H-NMR spectroscopy (400 MHz) and X-ray structure analysis. The methyl 2,3,4-tri-O-acetyl-6-O-triphenylmethyl--D-glucopyranoside and the N-(I-O-methyl-2,3,4-tri-O-acetyl--D-glucopyranose-6-yl)-pyridinium nitrate crystallize in the P2₁ space group with =14.940(1),b=11.232(1),c=9.0773(7), and =94.480(7) anda=7.670(1),b=15.384(3),c=9.624(1) and =104.90(1), respectively; the methyl 2,3,4-tri-O-acetyl-6-O-nitro--D-glucopyranoside and methyl 2,3,4-tri-O-acetyl-6-O-deoxy-6-iodo--D-glucopyrano-side crystallize in the P2₁2₁2₁ space group witha=5.630(1),b=14.360(1) andc=22.388(3), anda=5.556(1),b=14.303(6) andc=21.963(6), respectively.     

Synthesis,spectroscopic studies,and X-ray crystallographic analysis of the organophosphorus carbohydrate: methyl 4,6-O-benzylidene-3-deoxy-3-C-diphenylphosphinyl-α-D-altropyranoside

The synthesis and molecular structure determination of an organophosphorus carbohydrate are reported. In the solid state the molecules of methyl 4,6-O-benzylidene-3-deoxy-3-C-diphenyl-phosphinyl--D-altropyranoside are linked together by intermolecular hydrogen bonding involving the oxygen attached to phosphorus and the hydroxy group. The five-valent phosphorus atom is in a distorted tetrahedral environment. The chiral molecules crystallize in the monoclinic space groupP2₁ withZ+2. Results from¹ H.¹³C and³¹P NMR investigations together with IR data are presented.     

Calculation of the parameters of the X-ray diffraction station with adaptive segmented optics on the side beam from the wiggler of the Sibir’-2 storage ring

The mounting of an X-ray diffraction station on the side beam of a 19-pole superconducting wiggler makes it possible not only to use the central synchrotron radiation beam with a wavelength of 0.5 ?, but also to solve problems requiring softer X rays at a synchrotron radiation (SR) intensity exceeding that for the beams from the bending magnet. A numerical simulation of the formation of photon beams from a source and their transmission through the elements of the station (and through the station as a whole) allows one to calculate the parameters of the station, compare it with the existing analogs, determine its potential and actual efficiency of its elements, and estimate the adjustment quality. A numerical simulation of the SR source on the side beam from the wiggler and the focusing channel (segmented condenser mirror, monochromator with sagittal focusing by the segmented second crystal, and segmented focusing mirror) has been performed. The sizes of the focus and the divergence of rays in it are determined with allowance for the finite sizes of segments. The intensity of radiation with a wavelength ?? = 1.0 ? in the focus is determined taking into account the loss in the SR extraction channel and in the focusing channel. The values of the critical wavelength for the side beam from the wiggler and the wavelength resolution are calculated. The intensities in the X-ray diffraction pattern and its angular resolution are found.     

X-ray structural and molecular mechanics investigation of cyclopentadienyl-carbonyl-triphenylophosphine-phenylacetyliron, (η5-C5H5)Fe(CO)(PPh3)(COCH2C6H5)

The crystal and molecular structure of cyclopentadienyl-carbonyl-triphenylphosphine-phenylacetyl-iron (1) has been determined on the basis of X-ray data. The crystals are triclinic, space groupP¯1 (Z=2) with cell dimensions:a=9.546(1),b=10.233(1),c=5.012(2) Å,=93.70(1),=101.12(1), =112.58(1)°. The structure was solved by direct methods and refined anisotropically by a full-matrix, least-squares procedure against 4964 independent reflections, givingR=0.0416. The MM calculations done for a model of1 reproduced satisfactorily the X-ray structure.On leave from the Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai, China.     

Crystal and molecular structure of the (−)-N-hydroxyimide of (10-pinene-2-yl) succinimic acid

Two independent molecules in the unit cell are the same enantiomer of the title compound but possess slightly different conformations. Both conformers are joined by H-bonds to one water molecule. The configuration at C11 was established asR.Crystal data: C₁₄H₁₉O₃N×1/2H₂O; trigonal,P3₂;a=17.486(2),b=17.486(2),c=8.024(1)Å;V=2124.72(6)ų;Z=6; (CuK)=1.54178 Å;F(000)=834; finalR=0.0495 for 2376 reflections (of 2747 unique data).     

Synthesis,extended Hückel molecular orbital calculations,and X-ray diffraction structure of the pentamethylcyclopentadienylruthenium complex Cp*Ru(NO)(2,3-quinoxalinediolate)

The reaction between Cp^*Ru(NO)Cl₂ and the heterocyclic compound 2,3-quinoxalinediol in the presence of methanolic KOH leads to the formation of the new piano-stool compound Cp^*Ru(NO)(2,3-quinoxalinediolate) (1). Product isolation and characterization by solution spectroscopic methods (¹H and¹³C NMR and IR) are described. The solid-state structure of Cp^*Ru(NO)(2,3-quinoxalinediolate) confirms the replacement of each chloride ligand in Cp^*Ru(NO)Cl₂ by an oxygen group of the 2,3-quinoxalinediol ligand. Cp^*Ru(NO)(2,3-quinoxalinediolate) crystallizes in the orthorhombic space group Pbca, a=14.846(1) Å,b=12.718(1) Å,c=18.255(2) Å,V=3446.7(5) ų,Z=8,d _calc=1.643 g·cm^–3;R=0.0364,R _w=0.0393 for 1245 observed reflections withI>3(I). The observed Ru–N–O bond angle of 156.3(7)° in the X-ray structure of1 confirms the nonlinear nature of the nitrosyl linkage. This bend in the nitrosyl moiety away from the quinoxalinediolate ligand presumably results from solid-state packing forces and does not derive from electronic interactions, on the basis of extended Hückel molecular orbital calculations. The MO properties of1 are compared with other Cp^*Ru(NO)-substituted complexes previously synthesized in these laboratories.     

Determination and correlation of heavy atom positions in the derivatives used in the X-ray analysis of ribonuclease A at 2.5 Å resolution

The analysis of four heavy atom derivatives of ribonuclease A is described leading to isomorphous phasing at 2.5 resolution. Differences in the characteristics of the derivatives are discussed with respect to the determination of their heavy atom parameters and the correlation of sites between derivatives to produce a self consistent set. The criteria used to ensure consistency are described. In the final phase analysis using refined heavy atom parameters the least squaresR factors of the derivatives were .124, .143, .101, and .067 respectively, and the mean figure of merit for the 3444 observed reflexions was 0.66.In recognition of C. H. Carlisle's pioneering work in this field.     

Structural studies on molecular complexes,I: Crystal and molecular structure of 9-aminoacridine-sulfamethoxypyridazine (1∶1), C13H10N2·C11H12N4O3S

The crystal structure of the molecular complex of the antiseptic 9-aminoacridme and the sulfa drug sulfamethoxypyridazine (11), C₁₃H₁₀N₂·C₁₁H₁₂N₄O₃S, has been determined by X-ray diffraction methods. The crystals are orthorhombic: Pbca (No. 61),a=16.321(1),b=16.951(1),c=16.331(1) Å,Z=8,F(000)=1984, andV _c =4518.1(5) ų. The structural parameters have been refined to a finalR value of 0.046 for 3134 observed reflections. The results of X-ray analysis show that the structure contains an acridinium-sulfanilamidate ion pair. A hydrogen atom is transferred from the sulfonamide nitrogen atom to the nitrogen atom of the acridine ring, and an N(acridinium)-HN(sulfonamide) hydrogen bond is formed. A slight folding of the acridine moiety is observed.     

The crystal and molecular structure of one of the possible conformers of “the smallest piece of ice”—A solid-state isolation of a hydrogen bonded water hexamer trapped within channels of a crystal of a dirhodium molecule

Reexamination of our study of [Rh₂(HNOCCH₃)₄(2H₂O)] 3H₂O (Ahsan, M.Q.; Bernal, I.; Bear, J.L. Inorg. Chem. 1986, 26 260) showed it to be interesting not just because the dirhodium molecule is an antineoplastic but because it contains a hexameric cluster of waters trapped in Rh–Rh lattice cavities. It may well provide an interesting model for the smallest piece of ice (Nauta, K.; Miller, R.E. Science 2000, 287, 293).     

Crystal and molecular structure of 4,17a-methy1-4, 17a-diaza-5α-androstane (HS353): An intermediate in the design of azasteroid neuromuscular blocking agents

The crystal and molecular structure of 4, 17a-methyl-4, 17a-diaza-5-androstane (HS353), C₂₀N₂H₃₆ has been determined by direct methods and successive electron density calculations. The crystals are triclinic,a=7.419(2),b=20.300(4),c=12.866(2)Å,=105.91(2),=76.33(2),=99.32(2)°, space groupP1,Z=4. Block-matrix least-squares refinement converged toR=0.0660 for 3243 reflections withI3I (CuK radiation). The four independent molecules show only minor conformational variations, all rings being trans-connected chairs. Introduction of N at positions 4 and 17a of ringsA andD creates asymmetry in both conformation and bond angles, producing outward bending of the C-N side groups at both ends of all four molecules.Steroids and related studies, Part 83.