Richard Cooper

Nov 172010
 

Jeremy Law, a Part II student working with Dr Nick Rees and Dr David Watkin, has won a prize for his poster entitled “Alternative Approaches to Hydrogen Atom Location in the Solid State”. He presented his work to the joint ISIS Crystallography User Group and British Crystallographic Association PCG/SCMP meeting “Current Research in Physical Crystallography”

Nov 162010
 

Congratulations to Dr David Watkin who received an award under the Oxford Teaching Awards scheme for excellence in teaching as attested by student feedback and with the support of the department. He received a certificate presented by Professor Andrew Hamilton, the Vice-Chancellor of Oxford at Rhodes House.
The Oxford Teaching Awards scheme, co-ordinated by the Oxford University Learning Institute, recognises outstanding contributions award winners have made to teaching and learning at Oxford.

Jul 312010
 

CRYSTALS v14.11 is available as a beta-test.

Many small changes in Regularise Replace thanks to a CRYSTALS workshop in Toulouse organised by Carine Duhayon and Laure Vendier.

Cif generator now properly includes esds on refined hydrogen bonds, has incrreased figure-fields for cell parameters, and appends constraint and restraint information as _iucr_ data items at end of cif.

Improved scaling of difference Pattersons – see forthcoming paper by Flack, Sadki, Thompson & Watkin.

Absolute configuration routine (based on PLATON with Ton Spek’s permission) extended to provide more diagnostics and additional data to be re-input as absolute-structure strengthening restraints (see paper by Flack et al. above).

Error tracking for “USE” files has been improved.

Collaboration with Ernesto Mesto (Dipartimento Geomineralogico – Università degli Studi di Bari) uncovered over-sights in the original 1979 code, which lost contributions when a twin component fell onto a centring absence. Difference maps with twinned data now seem to reveal hydrogen atoms very reliably.

Jul 132010
 

Cryst. Rev. (2010), 16(3), 197-230.    [ doi:10.1080/08893110903483246 ]

X-ray single crystal structure analysis has become a gold standard for the determination of molecular geometry. The reliability of the technique is a triumph for science and technology working together. The uniqueness of well-crystalline material intrigued early natural philosophers, and their examinations, followed by the discovery of the diffraction of X-rays by crystals, led to the powerful technology that we now enjoy. For about three quarters of a century molecular structure determination has been a driving force for crystallographic research, but now that the science has matured into a technology, interest is returning in trying to understand the nature of crystals themselves.

Jun 292010
 

J. Appl. Cryst. (2010), 43, 1100-1107.    [ doi:10.1107/S0021889810025598 ]

Because they scatter X-rays weakly, H atoms are often abused or neglected during structure refinement. The reasons why the H atoms should be included in the refinement and some of the consequences of mistreatment are discussed along with selected real examples demonstrating some of the features for hydrogen treatment that can be found in the software suite CRYSTALS.

Hydrogen addition in CRYSTALS

Hydrogen addition in CRYSTALS

Electronic reprints:

Publisher’s copy:

Nov 182009
 

Acta Cryst. (2009), C65, o635-o638.    [ doi:10.1107/S0108270109046952 ]

The unusual methylene aziridine 6-tert-butyl-3-oxa-2-thia-1-azabicyclo[5.1.0]oct-6-ene 2,2-dioxide, C9H15NO3S, was found to crystallize with two molecules in the asymmetric unit. The structure was solved in both the approximately orthogonal and the oblique settings of space group No. 14, viz. P21/n and P21/c, respectively. A comparison of these results clearly displayed an increase in the correlation between coordinates in the ac plane for the oblique cell. The increase in the corresponding covariances makes a significant contribution to the standard uncertainties of derived parameters, e.g. bond lengths. Since there is yet no CIF definition for the full variance-covariance matrix, there are clear advantages to reporting the structure in the nonstandard space-group setting.

Publisher’s copy: IUCr

Oct 222009
 

Acta Cryst. (2009), E65, o2904-o2905.    [ doi:10.1107/S1600536809043827 ]

X-ray crystallographic analysis of the title hydrobromide salt, C10H20N+Br-, of (1R,2S,3R,5R,8aR)-3-hydroxymethyl-5- methyloctahydroindolizine-1,2-diol defines the absolute and relative stereochemistry at the five chiral centres in steviamine, a new class of polyhydroxylated indolizidine alkaloid isolated from Stevia rebaudiana (Asteraceae) leaves.

Electronic reprint:

Publisher’s copy:

Aug 012009
 

J. Appl. Cryst. (2009), 42, 798-809.    [ doi:10.1107/S0021889809024376 ]

A new method is presented for handling errors on crystallographic data. In single-crystal diffraction experiments, two variance-covariance matrices are present, one for the cell parameters and the second for the refined parameters (atomic coordinates and anisotropic displacement parameters). These two matrices can be combined so that errors on derived parameters, such as bond distances, bond angles and TLS tensors, may be calculated more simply. The new method works for all space groups but there are limitations on its application to triclinic space groups. The method allows errors to be transformed between space groups.

Publisher copy: IUCr

May 072009
 

Tet. Asym. (2009), 20, 712-717.    [ doi:10.1016/j.tetasy.2009.02.025 ]

Advances in hardware and software have made X-ray crystallography even more attractive as the first-option method for structure analysis. For most organic materials containing up to 100 non-hydrogen atoms, getting from the initial visual examination of the sample to producing publication-ready tables and pictures should usually be achievable in a single morning. Improvements in hardware have also increased reliability of the determination of absolute configuration. A recently published new algorithm may extend the range of applicability of the method.

Le Coup de Roi

Le Coup de Roi: making two chiral pieces from an achiral whole