Reinvestigation Of Structure Research Articles

Structure Reinvestigation of Gelsemoxonine, a Constituent of Gelsemium elegans, Reveals a Novel Azetidine‐Containing Indole Alkaloid.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A reinvestigation of the molecular structure of 4,4,8,8,12,12-hexamethyltrispiro[2,1,2,1,2,1]dodecane

The molecular structure of 4,4,8,8,12,12-hexamethyltrispiro[2,1,2,1,2,1]dodecane has been studied via ab initio molecular orbital calculations at the (HF/6-311G(d)and MP2/6-31G(d)) levels and gas phase electron diffraction. Both the calculations and electron diffraction data confirmed the presence of the twist-boat conformation. The principal geometrical parameters ( r g , ∠ α, Cp=cyclopropyl, and Me=methyl group) obtained from least squares analysis with constrains guided by calculations are as follows: r(C–H) av=1.102(5) Å, r(C 1–C 2)=1.567(3) Å, r(C 2–C 13)=1.519(4) Å, ∠C 3C 4C 5=117(2)°, ∠C MeC 1C 2=112.0(8)°, ∠HC MeC 1=109(3)°, ∠HC CpC 2=123(3)°, τ6123=31.3(14)°, τ1234=61.3(22)° and τ2345=27.9(1)°.

Structure reinvestigation of gelsemoxonine, a constituent of Gelsemium elegans, reveals a novel, azetidine-containing indole alkaloid.

[structure: see text] The structure of gelsemoxonine, isolated from Gelsemium elegans Benth., was revised to be a novel oxindole alkaloid having an azetidine unit. A new alkaloid, 14,15-dihydroxygelsenicine, which was presumed to be a biosynthetic precursor of gelsemoxonine, was also isolated.

Na12Ge17: A Compound with the Zintl Anions [Ge4]4— and [Ge9]4— — Synthesis, Crystal Structure, and Raman Spectrum

AbstractNa12Ge17 is prepared from the elements at 1025 K in sealed niobium ampoules. The crystal structure reinvestigation reveals a doubling of the unit cell (space group:P21/c; a = 22.117(3)Å, b = 12.803(3)Å, c = 41.557(6)Å, β = 91.31(2)°, Z = 16; Pearson code: mP464), furthermore, weak superstructure reflections indicate an even larger C‐centred monoclinic cell. The characteristic structural units are the isolated cluster anions [Ge9]4— and [Ge4]4— in ratio 1:2, respectively. The crystal structure represents a hierarchical cluster replacement structure of the hexagonal Laves phase MgZn2 in which the Mg and Zn atoms are replaced by the Ge9 and Ge4 units, respectively. The Raman spectrum of Na12Ge17 exhibits the characteristic breathing modes of the constituent cluster anions at ν = 274 cm—1 ([Ge9]4—) and ν = 222 cm—1 ([Ge4]4—) which may be used for identification of these clusters in solid phases and in solutions. Raman spectra further prove that Na12Ge17 is partial soluble both in ethylenediamine and liquid ammonia. The solution and the solid extract contain solely [Ge9]4—. The remaining insoluble residue is Na4Ge4. By heating the solvate Na4Ge9(NH3)n releases NH3 and decomposes irreversibly at 742 K, yielding Na12Ge17 and Ge.

Reinvestigation of the crystal structure of barium aluminum borate difluoride, BaAlBO3F2, a new nonlinear optical material

AlBBaF 2 O 3 , hexagonal, P6 (No. 174), a = 4.8879(6) A, c = 9.403(1) A, V = 194.5 A 3 , Z = 2, R gt (F) = 0.024, wR obs (F 2 ) = 0.036, T = 296K.

Reinvestigation of the GaMn structure and theoretical studies of its electronic and magnetic properties

The crystal structure of the binary gallide compound GaMn is reinvestigated using X-ray diffraction. The structure is quite different from that proposed previously. Although GaMn is reported to crystallize with the Al 8Cr 5 structure type, space group R3 m, we found that the centrosymmetric space group R 3 ̄ m , with a=12.605(2) Å and c=8.0424(11) Å, was more accurate. Moreover, the atomic positions and the atomic displacement parameters, which are missing in the previous study, are now refined. Thereafter, band structure calculations have been performed using the TB-LMTO-ASA method to understand the electronic and magnetic properties of this compound. Analyses from the band structure, the density of states and the magnetic moments obtained using spin-polarized calculations show the stability of two different magnetic models relative to the nonmagnetic one.

Reinvestigation of the Gas-Phase Structure of RDX Using Density Functional Theory Predictions of Electron-Scattering Intensities

Density functional calculations at the B3LYP/6-31G* level are used to generate electron-diffraction intensity curves for six conformers of hexahydro-1,3,5-trinitro-s-triazine (RDX). These are compared with an experimental curve (Shishkov, I. F.; Vilkov, L. V.; Lolonits, M.; Rozsondai, B. Struct. Chem. 1991, 2, 57) for which a structural model of gas-phase RDX was proposed. The calculations were done to investigate possible causes of the discrepancies between the theoretical structures and the molecular model proposed by Shishkov et al. The results show that alternative structures to that proposed from experiment can reproduce the measured intensities. Also, barriers to interconversion between the conformers were calculated to investigate the possibility of rapid interconversion at the temperature of the experiment (433 K). Barriers range from 1.5 to 5 kcal/mol, suggesting that measurements of RDX in the gas phase might reflect a dynamically averaged structure that represents contributions from the individual conformers.

Reinvestigation of the chemical structure of bitter-tasting quinizolate and homoquinizolate and studies on their Maillard-type formation pathways using suitable (13)C-labeling experiments.

Very recently, application of taste dilution analysis to heated xylose/alanine solutions led to the isolation of two bitter-tasting compounds exhibiting extraordinarily low detection thresholds of 0.00025 and 0.001 mmol/kg of water, respectively. On the basis of LC-MS and NMR spectroscopy, the structures of these compounds, named quinizolate and homoquinizolate, were proposed as 1-oxo-1H,4H-quinolizinium-7-olates. Since recent experiments in our laboratory shed some doubt on the entire correctness of their structures, labeling experiments with mixtures of multiply (13)C-labeled and nonlabeled pentoses were performed to follow the joint transfer of several (13)C atoms en bloc into the bitter compounds by LC-MS and NMR isotopomer diagnosis. The site-specific visualization of the mosaics assembled from (13)C-labeled and (12)C-labeled carbon modules in both bitter compounds demonstrated the structures of quinizolate and homoquinizolate to be the previously unknown (2E)-7-(2-furylmethyl)-2-(2-furylmethylidene)-3-(hydroxymethyl)- and (2E)-7-(2-furylmethyl)-2-(2-furylmethylidene)-3,8-bis(hydroxymethyl)-1-oxo-2,3-dihydro-1H-indolizinium-6-olate.

Neustädtelite and cobaltneustädtelite, the Fe3+- and Co2+-analogues of medenbachite

Neustädtelite and cobaltneustädtelite, two new minerals related to medenbachite, were found on samples from the dumps of the Güldener Falk mine near Schneeberg-Neustädtel, Saxony, Germany. The general appearance of the two new minerals is very similar: small tabular crystals up to 0.2 mm in diameter, transparent to translucent, with a brown color and a light brown streak; the lustre is adamantine. Both minerals are optically biaxial negative, 2V = 65(5)°, n x = 2.02(2), n y = 2.09 (calc.), n z = 2.12(2); pleochroism is strong with X = brown to opaque, Y = yellow, Z = pale yellow. Mohs’ hardness is 4.5. The cleavage parallel to {001} is good. The chemical compositions were derived by means of electron-microprobe analyses. Average contents for neustädtelite/cobaltneustädtelite are (in wt%): Bi 2 O 3 52.58/51.54, PbO 0.08/0.08, CaO 0.15/0.32, Fe 2 O 3 13.92/10.90, Al 2 O 3 0.29/0.07, CoO 3.35/5.47, NiO 0.34/1.61, ZnO 0.09/0.39, CuO 0.07/0.00, As 2 O 5 26.82/25.91, P 2 O 5 0.23/0.43, H 2 O (calc.) 2.56/3.01, total 100.48/99.73. Mössbauer spectra of cobaltneustädtelite and medenbachite confirmed that all of the iron is trivalent. Based on 12 O atoms, the empirical formulae for the neustädtelite and cobaltneustädtelite type materials are (Bi 1.94 Ca 0.02 ) ∑1.96 Fe 1.00 (Fe 0.50 Co 0.38 Ni 0.04 Al 0.05 Zn 0.01 Cu 0.01 ) ∑0.99 [(OH) 2.44 O 1.40 ] ∑3.84 [(AsO 4 ) 2.01 (PO 4 ) 0.03 ] ∑2.04 and (Bi 1.91 Ca 0.05 ) ∑1.96 Fe 1.02 (Co 0.63 Fe 0.16 Ni 0.19 Zn 0.04 Al 0.01 ) ∑1.03 [(OH) 2.88 O 1.12 ] ∑4.00 [(AsO 4 ) 1.95 (PO 4 ) 0.05 ] ∑2.00 , respectively. As derived from chemical analyses and crystal-structure investigations the ideal end-member compositions are Bi 2 Fe 3+ Fe 3+ O 2 (OH) 2 (AsO 4 ) 2 (neustädtelite) and Bi 2 Fe 3+ Co 2+ O(OH) 3 (AsO 4 ) 2 (cobaltneustädtelite). Extensive solid solution is observed between these two minerals. Neustädtelite and cobaltneustädtelite crystallize in space group P1̅; the cell parameters refined from powder data are a = 4.556(1)/9.156(1), b = 6.153(2)/6.148(1), c = 8.984(2)/9.338(1) Å, α = 95.43(2)/83.24(1), β = 99.22(2)/70.56(1), γ = 92.95(3)/86.91(1)°, V = 246.9/492.2 Å 3 , Z = 1/2, density (calc.) 5.81/5.81 g/cm 3 . Structure investigations were performed using single-crystal X-ray data. In both minerals edge-sharing alternating Fe 3+ Ø 6 and (Fe 3+ ,Co 2+ )Ø 6 /(Co 2+ ,Fe 3+) Ø 6 octahedra (Ø = O,OH) form chains parallel to [010] that are corner-linked by arsenate tetrahedra to layers parallel to (001). The Bi atoms are linked by O atoms to form columns parallel to [100]; these are sandwiched between layers of composition [6] M 2 (OH) 2 (AsO 4 ) 2 (M = Fe 3+ ,Co 2+ ). In neustädtelite the Bi atoms are site disordered; in cobaltneustädtelite half of the Bi atoms are ordered and half are on a split position. The partial ordering is induced by the presence of three OH groups, as compared to two in neustädtelite. A structural reinvestigation of medenbachite, Bi 2 Fe 3+ (Cu 2+ ,Fe 3+ )(O,OH) 2 (OH) 2 (AsO 4 ) 2 , proved isotypy with cobaltneustädtelite; the new cell parameters for medenbachite (refined from X-ray powder data) are: a = 9.162(2), b = 6.178(1), c = 9.341(2) Å, α = 83.50(2), β = 71.04(2), γ = 85.15(2)∞, V = 496 Å 3 , Z = 2.

A reinvestigation of the vibrational structure and the orbital assignments in the photoelectron bands of cyclopropane

The valence shell photoelectron spectrum of cyclopropane has been studied using synchrotron and HeI radiation. The photoelectron asymmetry parameters and branching ratios have been determined using monochromated synchrotron radiation in the photon energy range 15–120 eV. The spectral behaviour of the asymmetry parameters associated with the outer valence orbitals has been used to propose an assignment for the valence shell electronic configuration. The experimental features observed in the inner valence energy region of the photoelectron spectrum have been compared with theoretical predictions. The high resolution HeI excited spectrum has allowed vibrational structure to be observed in the outer valence photoelectron bands, and in two of the bands these features can be assigned to progressions involving the ν 2 (a 1′) and ν 11 (e′) modes. The X̃ 2E′ photoelectron band, which exhibits a doublet structure due to Jahn–Teller interaction, displays an extended vibrational progression in the doubly degenerate ν 11 (e′) mode.

A reinvestigation of the molecular structures, vibrations and rotation of methyl group in o-methylaniline in S 0 and S 1 states studied by laser induced fluorescence spectroscopy and ab initio calculations

The UV fluorescence excitation and dispersed fluorescence spectra of a jet-cooled o-methylaniline have been obtained for the S 1←S 0 transition, in which some of the bands have been observed and assigned for the first time. The origin of the electronic transition appears at 34,328.4 cm −1. It was found that the spectra exhibit an important feature corresponding to the internal rotation of the methyl group in the electronic ground and excited states. Ab initio calculations at MP2/6-31+G* and CIS/6-31+G* show that the optimised structure of o-methylaniline in the ground state is not planar with the amino group having sp 3 hybridation-like character due to the existence of lone paired electrons on the N atom. Upon electronic excitation, the CN bond exhibits a partial double character, as in the case of other aniline derivatives.

Re-investigation of SF2 hyperfine structure using transitions in the 26–34 GHz frequency range

The frequency range of the ETH Fourier transform microwave spectrometers has been extended to cover frequencies up to 40GHz.This new setup has been used to measure 26–34GHz rotational transitions of the unstable species SF2. The new hyperfine data obtained has allowed for a precise determination of the 19F spin–spin and spin–rotation coupling constants and for an accurate derivation of the 19F absolute nuclear shielding parameters.

1,2-Diiododisilane and 1,1,2,2-tetraiododisilane: a reinvestigation of the molecular structures and vibrational properties by gas-phase electron diffraction, temperature dependent Raman spectroscopy, and ab initio molecular orbital- and density functional calculations

The molecular structure, internal rotation and vibrational properties of 1,2-diiododisilane (DIDS), IH2Si–SiH2I, and 1,1,2,2-tetraiododisilane (TIDS), I2HSi–SiHI2, have been reinvestigated using gas phase electron diffraction (GED) data at temperatures of 55 (DIDS) and 155 (TIDS) °C, together with Raman spectroscopy, and ab initio molecular orbital (MO)- and density functional (DFT) calculations. The title compounds exist in the gas and liquid phases as a mixture of two conformers, anti (C2h), with a torsion angle φ (XSiSiX)=180°, and gauche (C2), with a torsion angle φ (XSiSiX) ≈60° (X=I (DIDS), X=H (TIDS)). Some structural parameter values obtained from the GED dynamic model refinements, using results from the theoretical calculations as constraints, were as follows (anti values with estimated 2σ uncertainties): For DIDS: Bond lengths (rg): r(Si–Si)=2.315(26) Å, r(Si–I)=2.447(6)Å. Bond angles (∠α): ∠SiSiI=107.5(10)°, ∠ISiH=109.8(5)°. For TIDS: Bond lengths (rg): r(Si–Si)=2.364(30)Å, r(Si–I)=2.450(6)Å, Bond angles (∠α): ∠SiSiI=107.2(4)°, ∠ISiH=109.9(2)°, ∠ISiI=111.7(3)°. Raman vibrational spectra for various temperatures are presented and analysed aided by normal coordinate calculations and the ab initio MO- and DFT results. From intensity variations with temperature of four band pairs for DIDS and two pairs for TIDS, conformational energies in the liquids were determined from van't Hoff plots. ΔH0(≈ΔE0) values of 0.31±0.14kcalmol−1 and 0.14±0.10kcalmol−1 were obtained for DIDS and TIDS respectively, gauche being the low energy conformer for both disilanes.

Synthesis and crystal structure of Ca 9Cu 1.5(PO 4) 7 and reinvestigation of Ca 9.5Cu(PO 4) 7

Ca 9Cu 1.5(PO 4) 7 was synthesized by the solid-state method at 1273 K followed by quenching in air. Crystal structure of Ca 9Cu 1.5(PO 4) 7 was refined by the Rietveld method: space group R3c, a = 10.3379(1) Å, c = 37.1898(3) Å, Z = 6 with R wp = 4.87%, R p = 3.67%, S = 1.58, R I = 2.42%, R F = 1.07%. The structure of Ca 9Cu 1.5(PO 4) 7 is isotypic with β-Ca 3(PO 4) 2 and Ca 9.5Cu(PO 4) 7. The M(5) site is fully occupied, and the M(4) site is half occupied by copper cations. The M(1)- M(3) sites are occupied by calcium cations. Copper cations in the M(4) site are displaced from the threefold axis due to long distances M(4)—O. Reinvestigation of crystal structure of Ca 9.5Cu(PO 4) 7 showed that the M(5) site is occupied by 0.79(1)Cu 2+ + 0.21Ca 2+, and other copper cations locate in the M(4) site.

The tetraethylammonium cation in a double three-ring silicate heteronetwork clathrate and a polyhedral clathrate hydrate: low-temperature single-crystal X-ray diffraction studies on (NEt 4) 6[Si 6O 15] · 40.8H 2O and NEt 4OH · 9H 2O

A reinvestigation of the crystal structure of the tetraethylammonium silicate hydrate with the approximate chemical composition (C 8H 20N) 6[Si 6O 15] · 40.8H 2O ( 1) is reported. The crystal structure of tetraethylammonium hydroxide nonahydrate, (C 8H 20N)OH · 9H 2O ( 2), has been determined for the first time. The structure of 1 has been refined to much higher precision in the centrosymmetric space group P 1(Z=2) with a considerable degree of disorder, compared to a previous structure analysis in the non-centrosymmetric space group P1 without disorder (Sov. Phys. Crystallogr. 29 (1984) 421). 1 may be considered as a host–guest compound, in which trigonal-prismatic double three-ring silicate anions and water molecules form a complicated hydrogen-bonded host structure. The organic guest cations reside in straight channels and very irregular, not completely closed cages. The [Si 6O 15] 6− oligoanions are stabilized in a specific organic–water environment by O–H ⋯ O hydrogen bonds and electrostatic and van der Waals O ⋯ CH 3 and O ⋯ CH 2( N) anion–cation interactions. The NEt + 4 cations occur as conformers of approximate 4 ̄ 2m(D 2d) and 4 ̄ (S 4) molecular symmetry, depending on the location around the oligoanion. 2 is the first representative of a polyhedral clathrate hydrate of the NEt + 4 cation. The novel host structure is built from hydrogen-bonded water molecules and hydroxide ions.

Preparation and Structure Determination of SrMn2(PO4)2 and Redetermination of b ′-Mn3(PO4)2

Pale rose single crystals of SrMn2(PO4)2 were obtained from a mixture of SrCl2 · 6 H2O, Mn(CH3COO)2, and (NH4)2HPO4 after thermal decomposition and finally melting at 1100 °C. The new crystal structure of strontium manganese orthophosphate [P-1, Z = 4, a = 8.860(6) A, b = 9.054(6) A, c = 10.260(7) A, α = 124.27(5)°, β = 90.23(5)°, γ = 90.26(6)°, 4220 independent reflections, R1 = 0.034, wR2 = 0.046] might be described as hexagonal close-packing of phosphate groups. The octahedral, tetrahedral and trigonal-bipyramidal voids within this [PO4] packing provide different positions for 8- and 10-fold [SrOx] and distorted octahedral [MnO6] coordination according to a formulation MnMnMnSr(PO4)4. Single crystals of β′-Mn3(PO4)2 (pale rose) were grown by chemical vapour transport (850 °C → 800 °C, P/I mixtures as transport agent). The unit cell of β′-Mn3(PO4)2 [P21/c, Z = 12, a = 8.948(2) A, b = 10.050(2) A, c = 24.084(2) A, β = 120.50°, 2953 independent reflections, R1 = 0.0314, wR2 = 0.095] contains 9 independent Mn2+. The reinvestigation of the crystal structure led to distinctly better agreement factors and significantly reduced standard deviations for the interatomic distances.

Structural relationships in crystals accommodating different stereoisomers of 2-amino-3-methylpentanoic acid.

A reinvestigation of the crystal structure of the 1:1 mixture of the two racemates DL-isoleucine and DL-allo-isoleucine, with a detailed analysis of interatomic distances between alternative side-chain positions, reveals a systematic distribution of the four stereoisomers in this crystal. Two different molecular chains exist in the crystal and each such chain accommodates a single diastereomeric pair only (L-isoleucine:D-allo-isoleucine or D-isoleucine:L-allo-isoleucine). The crystal is built up by a stacking of such chains in two dimensions and three different packing modes for the two types of chains are discussed. Crystallization experiments of the two individual racemates in the 1:1 mixture of DL-isoleucine:DL-allo-isoleucine have been undertaken. The structure of the racemate DL-isoleucine is presented. The molecular arrangements in this racemate and the 1:1 DL-isoleucine:DL-allo-isoleucine mixture are closely related. Furthermore, the spontaneous resolution of enantiomers upon crystallization of the other racemate, DL-allo-isoleucine, is rationalized on the basis of the aforementioned analysis of interatomic distances in the 1:1 DL-isoleucine:DL-allo-isoleucine complex. Structural data for a new L-isoleucine: D-allo-isoleucine complex are also given.

"NaB15": a new structural description based on X-ray and neutron diffraction, electron microscopy, and solid-state NMR spectroscopy

A boron-rich sodium boride, formerly known as NaB15, has been subjected to a comprehensive structural reinvestigation using X-ray single-crystal and powder diffraction, low-temperature neutron and electron diffraction, high-resolution transmission electron microscopy, and 23Na solid-state NMR spectroscopy. The results indicate that the previously published orthorhombic space group is incorrect. Consistent with all of the experimental results a modified structural description is developed in the monoclinic space group Ilml (a = 585.92(3), b= 1039.92(6), c = 833.17(5) pin, beta = 90.373(5) from powder data). Because one of the interstitial boron atom positions remains unoccupied, the accurate compositional formula is NaB145 or Na2B29.

Reinvestigation of the crystal structure of pentastrontium tetraniobate, Sr5Nb4O15

Article Reinvestigation of the crystal structure of pentastrontium tetraniobate, Sr5Nb4O15 was published on January 1, 2000 in the journal Zeitschrift für Kristallographie - New Crystal Structures (volume 215, issue 1).

A reinvestigation of the molecular structure of dimethyl-N-nitramine by gas electron diffraction, ab initio calculations of the molecular geometry and the force field and vibrational spectra

The molecular structure of dimethyl-N-nitramine was reinvestigated with gas-phase electron diffraction (ED) and ab initio calculations. Ab initio calculations using different basis sets and HF, MP2 and DFT all predict a molecule with Cs symmetry and a pyramidal amine N bond configuration. The vibrational spectra were interpreted from the scaling of the harmonic force field, and vibrational amplitudes required for the ED analysis were calculated from this scaled force field. The following values (rg bond lengths in Å and ∠α angles in degrees with errors equal to three standard deviations) were found for the main parameters: r(N–O)=1.232(3), r(N–N)=1.387(3), r(N–C)=1.466(3), r(C–H)ave=1.114(9), ∠CCN=116.1(6), ∠CNC=122.4(27), ∠ONO=127.6(12), ∠NCHave=109.9(18). The sum of the bond angles around the amine N atom is 354.6(28)°. The geometrical parameters obtained from the ED analysis are in agreement with the ab initio calculations except that a more pyramidal amine N bond configuration is predicted by ab initio.