Structure of the Month – April 2011

Apr 012011
 

Presented by: Nicholas G. White & Dr. Fabiola Zapata
Research Leader: Prof. Paul D. Beer
Published: Journal of the American Chemical Society

Both the mixed bromide/PF6 and mixed iodide/PF6 salt of this bis-iodoimidazolium macrocycle crystallize in the unusual cubic spacegroup I m -3 (there are currently only six organic structures in this spacegroup in the CSD).  The macrocycle binds anions strongly and selectively in competitive methanol/water solvent mixtures, with anions being bound solely by halogen-bonding interactions.  In the solid state, the both the bromide and iodide salts of the macrocycle exist as a dimer, with two macrocycles each pointing at two halide anions.  Experiments are being undertaken to see if this arrangement occurs in solution.

Structure of the Month - April 2011

Structure of the Month – April 2011

Miss Emma J. McKinley

Mar 162011
 

Emma’s research is focussed on developing a better understanding of the solid state.  She is using a three pronged attack, studying the crystallisation of chalcones; examining the effect of temperature on a material that undergoes a phase transition, and investigating the World’s Favourite Space Group, P21/c.  She is using a wide range of probes, including the Cambridge Structural Database, dSNAP, Laue Diffraction, Solid State NMR and Variable Temperature Single Crystal Diffraction as well as collecting data at Diamond.  When not fighting to grow crystals or preparing dinner for the team at Diamond, she enjoys dancing, but refuses to perform for the group.

ACA Annual Meeting 2010

Jul 292010
 

The ACA was held at the Sheraton Hotel in Chicago, IL.  Contributions from Chem. Cryst. include:

James Haestier, Amber L. Thompson, David J. Watkin, George C. Feast, Jeremy Robertson & Lee Page
Why is P21/n a Standard Non-Standard Space Group? (Poster)

Amber L. Thompson & David J. Watkin
Unpublishable” Data:  Does My R-factor Look Big in This? (Poster)

Amber L. Thompson
Absolute Structure Determination – Interpreting the Flack Parameter  (Presentation)

Handling Cell Errors in Crystallographic Data

Apr 152010
 

Cryst. Rev. (2010), 16(2), 133-144.    [ doi:10.1080/08893110903483238 ]

Recent developments in crystallographic error analysis are described. This report provides an introduction to more-formal work, originally published in Ref. (Haestier, J., J. Appl. Cryst. 2009, 42, 798). Prior to the main discussion, a brief overview of the normal distribution and error-propagation is provided, with some simplified examples to demonstrate the effects of covariance terms on error calculations. A new method is described for absorbing the cell-parameter errors into the variance-covariance matrix of the refined parameters. Problems occur for monoclinic and triclinic cell settings as the crystallographer must ‘choose’ how errors on the cell angles affect the coordinates. The choice has no effect on error-calculations on the internal geometry (bond-lengths, angles and torsion angles) of the structure, but may introduce a bias if the errors are used as weights.

BCA Spring Meeting 2010

Apr 152010
 
Susan Huth presents Kirsten Christensen with the Durward Cruickshank Award

Susan Huth presents Kirsten Christensen with the Durward Cruickshank Award

The final dinner of the British Crystallographic Association Spring Meeting in Warwick was interrupted, as always, with the prize winning awards. Amber Thompson was awarded the International Union of Crystallography Prize (a copy of International Tables) for her explanation of the advantages of choosing non-standard space groups. Kirsten Christensen was awarded the Durward Cruickshank prize for a young crystallographer who had made an outstanding contribution to crystallography.

 

 

Other contributions include:

N. David Brown, James Haestier, Mustapha Sadki, Amber L. Thompson & David J. Watkin
matchbOx:  Automatic Structure Matching to Facilitate Crystallographic Refinement (YC Presentation)

Kirsten E. Christensen, Christopher J. Serpell, Nicholas E. Evans & Paul D. Beer
Pushing the Boundaries of Small Molecule Crystallography:  The Challenging Structure of a Macrocyclic Anion Sensor (Poster)

Richard I. Cooper, Amber L. Thompson & David J. Watkin
The Hydrogen Challenge:  Where are we Now? (Poster)

Christopher J. Serpell & Paul D. Beer
Refinement of Large Supramolecular Structures (Presentation)

David J. Watkin
Dealing with Difficult Data (Session Chair)

 

An Unusual Methylene Aziridine Refined in P21/c and the Nonstandard Setting P21/n

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