Automated structure analysis in electron crystallography: phase determination with the tangent formula and least-squares refinement

1994 ◽  
Vol 50 (3) ◽  
pp. 287-292 ◽  
Author(s):  
D. L. Dorset ◽  
M. P. McCourt
Keyword(s):  
Least Squares ◽  
Structure Analysis ◽  
Electron Crystallography ◽  
Phase Determination

Direct phase determination in electron crystallography: small organic molecules

1992 ◽  
Vol 50 (2) ◽  
pp. 1166-1167
Author(s):  
Douglas L. Dorset
Keyword(s):  
Organic Molecules ◽  
Data Sets ◽  
Temperature Structure ◽  
3D Analysis ◽  
Intensity Data ◽  
Electron Crystallography ◽  
Phase Determination ◽  
Measured Intensity ◽  
3D Data

The quantitative use of electron diffraction intensity data for the determination of crystal structures represents the pioneering achievement in the electron crystallography of organic molecules, an effort largely begun by B. K. Vainshtein and his co-workers. However, despite numerous representative structure analyses yielding results consistent with X-ray determination, this entire effort was viewed with considerable mistrust by many crystallographers. This was no doubt due to the rather high crystallographic R-factors reported for some structures and, more importantly, the failure to convince many skeptics that the measured intensity data were adequate for ab initio structure determinations.We have recently demonstrated the utility of these data sets for structure analyses by direct phase determination based on the probabilistic estimate of three- and four-phase structure invariant sums. Examples include the structure of diketopiperazine using Vainshtein's 3D data, a similar 3D analysis of the room temperature structure of thiourea, and a zonal determination of the urea structure, the latter also based on data collected by the Moscow group.

Die Röntgenstrukturanalyse von (CO)9Co3CΟΒΒr2Ν(C5)3. X-ray Structure Analysis of (CO)9Co3COBBr2N(C2H5)3

1976 ◽  
Vol 31 (3) ◽  
pp. 342-344 ◽  
Author(s):  
Volker Bätzel
Keyword(s):  
Least Squares ◽  
Structure Analysis ◽  
Reliability Index ◽  
Three Dimensional ◽  
Diagonal Matrix ◽  
Crystal Data ◽  
Block Diagonal Matrix ◽  
Fourier Methods ◽  
Space Group ◽  
X Ray

Using three dimensional X-ray data collected on a four circle diffractometer, the structure of (CO)9Co3COBBr2N(C2H5)3 was solved by Patterson and Fourier methods. Least squares refinement with a block-diagonal matrix leads to a reliability index of R = 10.7%. Crystal data: α = 13.277(6) Å, b = 10.17(1) Å, c = 9.22(2) Å; α = 91.12(6)°, β = 87.61(4)°, γ = 98.79(2)°; space group P1̅; Z = 2; V = 1229,7 Å3; Dx = 1.97 gcm-3.

Rearrangement of 10-acetoxy-10-vinylcamphene

1982 ◽  
Vol 60 (8) ◽  
pp. 1055-1061 ◽  
Author(s):  
Nancy Lamb ◽  
Thomas Money ◽  
Steven J. Rettig ◽  
James Trotter
Keyword(s):  
Least Squares ◽  
Structure Analysis ◽  
Alkaline Hydrolysis ◽  
Direct Methods ◽  
Full Matrix ◽  
Space Group ◽  
Hydrolysis Of

Treatment of 10-acetoxy-10-vinylcamphene with BF3 or HClO4 results in rearrangement to a bicyclo[3.2.1]octane derivative in preference to 5-endo-trigonal cyclization. Alkaline hydrolysis of this bicyclooctane yields a diol, crystals of which are orthorhombic, a = 9.571(1), b = 12.416(1), c = 18.860(2) Å, Z = 8, space group C2221. The structure was solved by direct methods and was refined by a full-matrix least-squares procedure to R = 0.035 and Rw = 0.044 for 930 reflections with I ≥ 3σ(I). The structure analysis has unambiguously identified the diol as 2,3-dimethyl-4-vinylbicyclo[3.2.1]octan-2,3-diol.

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