Accuracy of linear polymer crystal structures determined from electron diffraction intensities: Problems with zonal data

1983 ◽  
Vol 41 ◽  
pp. 22-23
Author(s):  
Douglas L. Dorset
Keyword(s):  
Crystal Structure ◽  
Electron Diffraction ◽  
Structural Information ◽  
Structure Refinement ◽  
Diffraction Theory ◽  
X Ray Diffraction ◽  
X Ray ◽  
Multidimensional Parameter ◽  
Unknown Structure ◽  
Refinement Process

In contrast to analyses based on X-ray and neutron diffraction intensity data, electron crystal structure determination for organic materials is only a crudely-developed procedure. Although the pioneering work of Vainshtein and co-workers has been very important for realization of the technique's advantages, self-consistent procedures based on earlier-derived diffraction theory have only recently emerged, enabling a reasonable estimate of what structural information might be obtained from a given microcrystalline organic specimen and how this might be best achieved. Problems which are unresolved include the optimal refinement procedure for an unknown structure and also the adequate identification of the correct crystal structure during this refinement process.The behavior of the crystallographic residual(R) during structure refinement is manifested by various minima in a multidimensional parameter space. The description of this space is more complicated for electron diffraction than for X-ray diffraction, although both cases include atomic position, atomic thermal vibration, atomic occupancy, “extinction”, and crystal distortion.

scholarly journals Redetermination of Sr2PdO3 from single-crystal X-ray data

2019 ◽  
Vol 75 (1) ◽  
pp. 30-32
Author(s):  
Gohil S. Thakur ◽  
Hans Reuter ◽  
Claudia Felser ◽  
Martin Jansen
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Diffraction Data ◽  
Structure Refinement ◽  
Structure Type ◽  
X Ray Diffraction ◽  
High Quality ◽  
X Ray ◽  
Cell Parameters ◽  
Anisotropic Displacement Parameters

The crystal structure redetermination of Sr2PdO3 (distrontium palladium trioxide) was carried out using high-quality single-crystal X-ray data. The Sr2PdO3 structure has been described previously in at least three reports [Wasel-Nielen & Hoppe (1970). Z. Anorg. Allg. Chem. 375, 209–213; Muller & Roy (1971). Adv. Chem. Ser. 98, 28–38; Nagata et al. (2002). J. Alloys Compd. 346, 50–56], all based on powder X-ray diffraction data. The current structure refinement of Sr2PdO3, as compared to previous powder data refinements, leads to more precise cell parameters and fractional coordinates, together with anisotropic displacement parameters for all sites. The compound is confirmed to have the orthorhombic Sr2CuO3 structure type (space group Immm) as reported previously. The structure consists of infinite chains of corner-sharing PdO4 plaquettes interspersed by SrII atoms. A brief comparison of Sr2PdO3 with the related K2NiF4 structure type is given.

scholarly journals Crystal structure refinement of magnesium zinc divanadate, MgZnV2O7, from powder X-ray diffraction data

2021 ◽  
Vol 77 (6) ◽  
pp. 588-591
Author(s):  
Stephanie J. Hong ◽  
Jun Li ◽  
Mas A. Subramanian
Keyword(s):  
Crystal Structure ◽  
Diffraction Data ◽  
Structure Refinement ◽  
Atomic Ratio ◽  
Asymmetric Unit ◽  
X Ray Diffraction ◽  
X Ray ◽  
Trigonal Bipyramidal ◽  
Wyckoff Position ◽  
Distorted Trigonal Bipyramidal

The crystal structure of magnesium zinc divanadate, MgZnV2O7, was determined and refined from laboratory X-ray powder diffraction data. The title compound was synthesized by a solid-state reaction at 1023 K in air. The crystal structure is isotypic with Mn0.6Zn1.4V2O7 (C2/m; Z = 6) and is related to the crystal structure of thortveitite. The asymmetric unit contains two metal sites with statistically distributed magnesium and zinc atoms with the atomic ratio close to 1:1. One (Mg/Zn) metal site (M1) is located on Wyckoff position 8j and the other (M2) on 4h. Three V sites (all on 4i), and eight O (three 8j, four 4i, and one 2b) sites complete the asymmetric unit. The structure is an alternate stacking of V2O7 layers and (Mg/Zn) atom layers along [20\overline{1}]. It is distinct from other related structures in that each V2O7 layer consists of two groups: a V2O7 dimer and a V4O14 tetramer. Mixed-occupied M1 and M2 are coordinated by oxygen atoms in distorted trigonal bipyramidal and octahedral sites, respectively.

Synthesen, Kristallstrukturen und magnetische Eigenschaften von [Li(12-Krone-4)2][Li(12-Krone-4)(OH2)]2[Nb6Cl18], [Li(15-Krone-5)2(OH2)]3[Nb6Cl18] und [(18-Krone-6)2(O2H5)]3[Nb6Cl18] / Syntheses, Crystal Structures and Magnetic Behaviour of [Li(12-Krone-4)2][Li(12-Krone-4)(OH2)]2[Nb6Cl18], [Li(15-Krone-5)2(OH2)]3[Nb6Cl18] and [(18-Krone-6)2(O2H5)]3[Nb6Cl18]

2001 ◽  
Vol 56 (10) ◽  
pp. 1025-1034 ◽  
Author(s):  
Markus Ströbele ◽  
H.-Jtirgen Meyer
Keyword(s):  
Crystal Structure ◽  
Water Molecule ◽  
Crown Ethers ◽  
Magnetic Measurements ◽  
Structure Refinement ◽  
Magnetic Behaviour ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Paramagnetic Behaviour

The title compounds were prepared through reactions of Li2Nb6Cl16 with the corresponding crown ethers in acetone. All three compounds were obtained as dark brown crystals. Their structures were solved with the means of single-crystal X-ray diffraction.[Li(12-crown-4)2][Li(12-crown-4)(OH2)]2[Nb6Cl18]: space group P21/n, Z =2, a = 1320.4(1), b = 1879.1(1), c = 1321.7(1) pm, ß = 92.515(6)°, R1 = 0.0297 (I>2σ(I)). The crystal structure contains Li+ sandwiched by two 12-crown-4-ethers plus Li+ coordinated by one 12-crown-4- ether and one water molecule.[Li(15-crown-5)2(OH2)]3[Nb6Cl18]: space group R3̅, Z = 3, a = b = 2081.7(1), c = 1991.7(1) pm, R1 = 0.0395 (I > 2σ(I)). In the crystal structure Li+ and one water molecule are sandwiched by two 15-crown-5-ethers.[(18-crown-6)2(O2H5)]3[Nb6Cl18]: space group P1̅, Z = 1 ,a = 1405.1(1), b = 1461.1(2), c = 1492.2(2) pm; α = 98.80(1)°, ß = 98.15(1)°, γ = 97.41(1)°, R1 = 0.0538 (I > 2σ(I)). H5O2+ was found in the structure refinement sandwiched between two 18-crown-6-ethers.All compounds reported contain [Nb6Cl18] clusters with Nb-Nb distances between 299 and 301 pm. The paramagnetic behaviour expected for [Nb6Cl18]3- in all three compounds was confirmed by magnetic measurements.

Ideal and Real Structure of Ti5O4(PO4)4: X-ray and HRTEM Investigations

1998 ◽  
Vol 54 (6) ◽  
pp. 722-731 ◽  
Author(s):  
F. Reinauer ◽  
R. Glaum
Keyword(s):  
Crystal Structure ◽  
Electron Microscopy ◽  
Structure Refinement ◽  
Ideal Structure ◽  
Crystal Data ◽  
Asymmetric Unit ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
The Ideal

The crystal structure of pentatitanium tetraoxide tetrakis(phosphate), Ti5O4(PO4)4, has been determined and refined from X-ray diffraction single-crystal data [P212121 (No. 19), Z = 4, a = 12.8417 (12), b = 14.4195 (13), c = 7.4622 (9) Å (from Guinier photographs); conventional residual R 1 = 0.042 for 2556 Fo > 4σ(Fo ), R 1 = 0.057 for all 3276 independent reflections; 282 parameters; 29 atoms in the asymmetric unit of the ideal structure]. The structure is closely related to those of β-Fe2O(PO4)-type phosphates and synthetic lipscombite, Fe3(PO4)4(OH). While these consist of infinite chains of face-sharing MO6 octahedra, in pentatitanium tetraoxide tetrakis(phosphate) only five-eighths of the octahedral voids are occupied according to □3Ti5O4(PO4)4. Four of the five independent Ti4+O6 show high radial distortion [1.72 ≤ d(Ti−O) ≤ 2.39 Å] and a typical 1 + 4 + 1 distance distribution. The fifth Ti4+O6 is an almost regular octahedron [1.91 ≤ d(Ti−O) ≤ 1.98 Å]. Partial disorder of Ti4+ over the available octahedral voids is revealed by the X-ray structure refinement. High-resolution transmission electron microscopy (HRTEM) investigations confirm this result.

Al analogue of chayesite from a lamproite of Cancarix, SE Spain, and its crystal structure

2020 ◽  
Vol 196 (3) ◽  
pp. 193-198
Author(s):  
Natalia V. Zubkova ◽  
Nikita V. Chukanov ◽  
Christof Schäfer ◽  
Konstantin V. Van ◽  
Igor V. Pekov ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Diffraction Data ◽  
Empirical Formula ◽  
Structure Refinement ◽  
Crystal Chemical ◽  
Chemical Formula ◽  
Crystal Chemical Formula ◽  
X Ray Diffraction ◽  
Se Spain ◽  
X Ray

Al analogue of chayesite (with Al > Fe3+) was found in a lamproite from Cancarix, SE Spain. The mineral forms green thick-tabular crystals up to 0.4 mm across in cavities. The empirical formula derived from EMP measurements and calculated on the basis of 17 Mg + Fe + Al + Si apfu is (K0.75 Na0.20 Ca0.11)Mg3.04 Fe0.99 Al1.18 Si11.80 O30. The crystal structure was determined from single crystal X-ray diffraction data ( R = 2.38%). The mineral is hexagonal, space group P 6/ mcc, a = 10.09199(12), c = 14.35079(19) Å, V = 1265.78(3) Å3, Z = 2. Fe is predominantly divalent. Al is mainly distributed between the octahedral A site and the tetrahedral T 2 site. The crystal chemical formula derived from the structure refinement is C (K0.73 Na0.16 Ca0.11)B (Na0.02)4 A(Mg0.42 Al0.29 Fe0.29)2 T 2(Mg0.71 Fe0.16 Al0.13)3 T 1(Si0.985 Al0.015)12 O30.

Synthese, Schwingungs- und Massenspektren von Et2Sn(O2PR2)2 (R = Me, Ph); Kristallstruktur von Et2Sn(O2PPh2)2 / Synthesis, Vibrational Spectra and Mass Spectra of Et2Sn(O2PR2)2 (R = Me, Ph); Crystal Structure of Et2Sn(O2PPh2)2

1996 ◽  
Vol 51 (8) ◽  
pp. 1111-1116 ◽  
Author(s):  
Abdel-Fattah Shihada ◽  
Frank Weller
Keyword(s):  
Crystal Structure ◽  
Vibrational Spectra ◽  
Mass Spectra ◽  
Structure Refinement ◽  
Base Peak ◽  
Trans Position ◽  
X Ray Diffraction ◽  
X Ray ◽  
Octahedral Environment ◽  
In Trans

Et2Sn(O2PPh2)2 has been synthesized by the reaction of (Et2ClSn)2O with Ph2POCl in toluene and by the treatment of (Et2ClSn)2O or Et2SnCl2 with HO2PPh2 in methanol. The reaction of Et2SnO with HO2PMe2 in toluene was used to prepare Et2Sn(O2PMe2)2. An X-ray diffraction study of Et2Sn(O2PPh2)2 (space group P1̅, Z = 1, a = 559,9( 1), b = 983,7(1), c = 1262,4(l)pm, α = 81,85( 1 )°, β = 79,79( 1)°, γ = 75,00(1)°; structure refinement with 2662 independent reflections, R = 0.055) shows that the structure is polymeric and the O2PPh2 ligands function as double bridges between the tin atoms leading to the formation of centrosymmetric Sn2O4P2 eight-membered rings. The ethyl groups are in trans-position in the resulting octahedral environment around tin. The I. R. and Raman spectra of Et2Sn(O2PR2)2 (R = Ph, Me) have been discussed and assigned. The mass spectra of Et2Sn(O2PR2)2 show Sn(O2PR2)+ as the base peak.

Ammoniovoltaite, (NH4)2Fe2+5Fe3+3Al(SO4)12(H2O)18, a new mineral from the Severo-Kambalny geothermal field, Kamchatka, Russia

2018 ◽  
Vol 82 (5) ◽  
pp. 1057-1077 ◽  
Author(s):  
Elena S. Zhitova ◽  
Oleg I. Siidra ◽  
Dmitry I. Belakovsky ◽  
Vladimir V. Shilovskikh ◽  
Anton A. Nuzhdaev ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Room Temperature ◽  
Structure Refinement ◽  
Geothermal Field ◽  
Water Soluble ◽  
Ammonium Ion ◽  
New Mineral ◽  
X Ray Diffraction ◽  
X Ray ◽  
Mössbauer Data

AbstractAmmoniovoltaite, (NH4)2Fe2+5Fe3+3Al(SO4)12(H2O)18, is a new voltaite-group mineral. The mineral was discovered at the Severo-Kambalny (North-Kambalny) geothermal field, Kambalny volcanic ridge, Southern Kamchatka, Russia. Ammoniovoltaite forms at ~100°C around geothermal gas/steam vents in association with alunogen, tschermigite and pyrite. Crystals of ammoniovoltaite have euhedral habit, are up to 50 µm in size and grow on alunogen plates. Ammoniovoltaite is black with vitreous lustre, opaque, brittle and water-soluble. Neither cleavage nor parting is found, the fracture is conchoidal. The mineral is isotropic, with the refractive index n = 1.602(2) (589 nm). Infrared spectra contain an absorption band at 1433 cm–1 distinctive for the ammonium ion. The chemical composition is (iron content is given in accordance with Mössbauer data, H2O calculated from a crystal-structure refinement, wt.%): FeO 13.26, Fe2O3 11.58, MgO 2.33, ZnO 0.04, Al2O3 2.74, SO3 47.46, K2O 0.19, CaO 0.11, (NH4)2O 2.96, H2O 16.03, total 96.70. The empirical formula based on S = 12 atoms per formula unit is [(NH4)1.88K0.08Ca0.04]Σ2.00(Fe2+3.74Mg1.17Fe3+0.05Zn0.01)Σ4.97(Fe3+2.89Al0.09)Σ2.98Al1.00(SO4)12.00(H2O)18.00. The crystal structure has been refined to R1 = 0.031 and 0.030 on the basis of 1217 and 1462 unique reflections with I >2σ(I) collected at 100 K and room temperature, respectively. Ammoniovoltaite is the ammonium analogue of voltaite. The mineral is cubic, Fd$\bar{3}$c, a = 27.250(1) Å and V = 20234(3) Å3 (at 100 K); and a = 27.322(1) Å and V = 20396(3) Å3 (at RT), with Z = 16. The strongest lines of the powder X-ray diffraction pattern [d, Å (I, %) (hkl)] are: 9.67 (74) (022), 7.90 (56) (222), 5.58 (84) (422), 3.560 (100) (731), 3.418 (100) (008) and 2.8660 (37) (931). A brief review of ammonium minerals from various volcanically active geological environments is given.

scholarly journals Barysilite from Garpenberg Norra, Dalarna, Sweden: occurrence and crystal structure refinement

2002 ◽  
Vol 66 (2) ◽  
pp. 353-363 ◽  
Author(s):  
U. Kolitsch ◽  
D. Holtstam
Keyword(s):  
Crystal Structure ◽  
Lone Electron Pair ◽  
Electron Pair ◽  
Divalent Cations ◽  
Structure Refinement ◽  
Direct Proof ◽  
Structural Formula ◽  
X Ray Diffraction ◽  
X Ray ◽  
Area Detector

AbstractA new occurrence of barysilite, Pb8Mn(Si2O7)3, at the polymetallic Garpenberg Norra Zn-Pb deposit, Hedemora, Dalarna, Sweden, is described. The mineral, which forms colourless, transparent grains, is characterized by X-ray diffraction and electron-microprobe analyses. The assemblage includes tephroite, zincian jacobsite, manganoan diopside and others. The crystal structure of a barysilite crystal from Garpenberg Norra was redetermined using single-crystal X-ray diffraction data (Mo-Kα, CCD area detector) and has been refined in space group R3̄c with a = 9.804(1), c = 38.416(8)Å, V = 3197.8(8)Å3, to R1 = 2.32% for 1025 ‘observed’ reflections with Fo >4σ(Fo). A previous, low-precision structure determination (Lajzérowicz, 1965; R = 20%) is confirmed but improved considerably. The structure contains one distorted MnO6 polyhedron with six equivalent Mn–O bonds (2.224 Å), one Si2O7 disilicate unit with an Si–O–Si angle of 120.9°, and two non-equivalent Pb sites. The Pb1 site has a highly irregular, one-sided coordination with six O ligands, indicating a stereoactive 6s2 lone-electron pair on the Pb2+ ion, whereas the [6+3]-coordinated Pb2 site is fairly regular, with Pb–O distances of 2.540 (3×), 2.674 (3×) and 3.098 (3×) Å. The Pb2 site contains ~10% of Ca (+Ba) replacing Pb, corresponding to the structural formula Pb16(Pb,Ca)22Mn(Si2O7)3. This is the first direct proof that not only the M site in barysilite-type Pb8M(Si2O7)3 compounds can be replaced by divalent cations.

SU-79: a novel germanate with 3D 10- and 11-ring channels templated by a square-planar nickel complex

2014 ◽  
Vol 1 (3) ◽  
pp. 278-283 ◽  
Author(s):  
Shiliang Huang ◽  
Jie Su ◽  
Kirsten Christensen ◽  
A. Ken Inge ◽  
Jie Liang ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Electron Diffraction ◽  
Single Crystal ◽  
Nickel Complex ◽  
X Ray Diffraction ◽  
X Ray ◽  
Open Framework ◽  
Square Planar

An open-framework germanate SU-79 was synthesized using nickel complex and amine as the templates. The crystal structure was solved by the combination of rotation electron diffraction (RED) and synchrotron single crystal X-ray diffraction.

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