Dec 202012
 
DetOx: A Program for Determining Anomalous Scattering Factors of Mixed-Oxidation-State Species (K.J. Sutton, S.A. Barnett, K.E. Christensen, H. Nowell, A.L. Thompson, D.R. Allan and R.I. Cooper)

J. Sync. Rad (2013). 20, 200–204. [ doi:10.1107/S0909049512044007 ]

Overlapping absorption edges will occur when an element is present in multiple oxidation states within a material. DetOx is a program for partitioning overlapping X-ray absorption spectra into contributions from individual atomic species and computing the dependence of the anomalous scattering factors on X-ray energy. … Read the rest

Sep 212012
 
CRYSTALS Enhancements: Asymmetric Restraints (R. I. Cooper, A. Thorn and D. J. Watkin)

J. Appl. Cryst. (2012). 45, 1057–1060. [ doi:10.1107/S0021889812035790 ]

The traditional Waser distance restraint, the rigid-bond restraint and atomic displacement parameter (ADP) similarity restraints have an equal influence on both atoms involved in the restraint. This may be inappropriate in cases where it can reasonably be expected that the precision of the determination of … Read the rest

Apr 302012
 
Applications of Leverage Analysis in Structure Refinement (S. Parsons, T. Wagner, O. Presly, P. A. Wood and R. I. Cooper)

J Appl. Cryst. (2012), 45, 417-429. [ doi:10.1107/S0021889812015191 ]

Leverages measure the influence that observations (intensity data and restraints) have on the fit obtained in crystal structure refinement. Further analysis enables the influence that observations have on specific parameters to be measured. The results of leverage analyses are discussed in the context of the … Read the rest

Mar 192012
 
Alkyl-chain Disorder in Tetraisohexylammonium Bromide (M. A. Kelland and A. L. Thompson)

Acta Cryst.  (2012), C68, o152-o155.    [ doi:10.1107/S0108270112009377 ]

Tetraisohexylammonium bromide [systematic name: tetrakis(4-methylpentyl)azanium bromide], C24H52N+·Br, is a powerful structure II clathrate hydrate crystal-growth inhibitor. The crystal structure, in the space group P3221, contains one ammonium cation and one bromide anion in the asymmetric unit, … Read the rest

Feb 192012
 
An Integrated X-ray and Molecular Dynamics Study of Uranyl-salen Structures and Properties (G. M. Lombardo,  A. L. Thompson,  F. P. Ballistreri,  A. Pappalardo,  G. T. Sfrazzetto,  G. A. Tomaselli,  R. M. Toscano and F. Punzo)

Dalton Trans. (2012), 41, 1951-1960.    [ doi:10.1039/C1DT11758K ]

Uranium complexes of bis(p-tert-butyl-salicylidene)-1,2-diphenylethylenediamine (1) and bis(salicylidene)-1,2-diphenylethylenediamine (2) have been synthesized and investigated by X-ray single crystal diffraction and MD calculations in Periodic Boundary Conditions. Both compounds form crystals which are densely packed and do not provide voids accessible to … Read the rest

Feb 032012
 
Methyl 6-amino-6-oxohexanoate & 3-Methoxy-3-oxopropanaminium chloride (T. Gruber, C. J. Schofield and A. L. Thompson)

Acta Cryst. (2012), E68, o593-o594.    [ doi:10.1107/S1600536812003303 ]

The title compound, C7H13NO3, adopts an approximately planar conformation. The torsion angles in the aliphatic chain between the carbonyl group C atoms range from 172.97 (14) to 179.38 (14)° and the r.m.s. deviation of all non-H atoms is 0.059 Å. … Read the rest

Sep 132011
 
CRYSTALS Enhancements:  Absolute Structure Determination (A. L. Thompson and D. J. Watkin)

J. Appl. Cryst.  (2011), 44, 1017-1022.    [ doi:10.1107/S0021889811034066 ]

A summary of the features for investigating absolute structure available in the crystallographic refinement program CRYSTALS is presented, together with the results of analyses of 150 light-atom structures collected with molybdenum radiation carried out with these tools. The results confirm that the Flack and Hooft … Read the rest

Feb 152011
 
Chiral Selection in the Formation of Borates from Racemic Binaphthols and Related Diols (J. A. Raskatov, J. M. Brown and A. L. Thompson)

CrystEngComm (2011), 13(8) 2923-2929.    [ doi:10.1039/c0ce00709a ]

A series of racemic or stereochemically labile chiral borate anions based on the 2,20-biphenol motif was
investigated. All borates were homochiral in the solid state, although in some cases the heterochiral
diastereomers were computed to be thermodynamically preferred (DFT). The crystallographic
preference for the homochiral diastereomer was … Read the rest

Dec 072010
 
Practical Applications of Averages and Differences of Friedel Opposites (H. D. Flack, M. Sadki, A. L. Thompson and D. J. Watkin)

Acta Cryst. (2011), A67, 21-34.    [ doi:10.1107/S010876731004287X ]

The practical use of the average and difference intensities of Friedel opposites at different stages of structure analysis has been investigated. It is shown how these values may be properly and practically used at the stage of space-group determination. At the stage of least-squares refinement, … Read the rest

Nov 272010
 

J. Appl. Cryst. (2011), 44, 52-59.    [ doi:10.1107/S0021889810042470 ]

One of the requirements for the next generation of small-molecule crystallographers is a mathematical programming infrastructure. It should provide a modelling design process, where the model formulation is kept separate from the optimization process to provide gains in reliability, scalability and extensibility, enabling the application … Read the rest