Variable Temperature – Chemical Crystallography

Some Experimental Aspects of Absolute Configuration Determination using Single Crystal X-Ray Diffraction

Nov 012017

Tetrahedron Asymmetry 2017, 28(10), 1330-1336 [doi:10.1016/j.tetasy.2017.08.016]

Students of single crystal X-ray diffraction are often give advice as to how best to collect their data when attempting absolute configuration determination. These ‘rules’ often have more grounding in gut-feeling than evidence. Thus, in an effort to provide advice and evidence that today’s crystallographers can pass onto to tomorrow’s young scientists, we present a systematic study of 1-deoxy-L-arabinitol, a straight chain sugar which crystallizes well in the space group I4₁.

Publisher’s copy: Science Direct
Oxford University Research Archive (ORA)

Structure of the Month – November 2012

Nov 012012

Presented by: Vanessa E. Fairbank & Dr. Amber L. Thompson
Research Leader: Dr. Andrew L. Goodwin
Published: Physical Review B

Cubic Cd(CN)₂ shows the strongest known isotropic negative thermal expansion (NTE; volume contraction on heating). Variable-temperature single-crystal X‑ray diffraction suggests there is temperature-dependent off-centering of Cd²⁺ ions that has the effect of increasing the cadmium coordination volume at low temperatures, providing an alternate mechanism for NTE in this material. These displacements are evident in the residual electron density and the highly-structured diffuse scattering in the experimental X-ray diffraction patterns. Using Monte Carlo simulations, we have interpreted these patterns in terms of a basic set of “ice-rules” that establish a mapping between the dynamics of Cd(CN)₂and proton ordering in cubic ice VII.

Structure of the Month – November 2012

Mr. William M. Brennan

Oct 102012

Will is working with Nick Rees, looking into the host/guest complexes of deoxycholic acid. Using variable temperature single crystal diffraction, along with Solid State NMR and Differential Scanning Calorimetry the project is particularly focused on phase changes within the crystal as a function of temperature. When not in the lab he enjoys long lunches, and competing for the Oxford Modern Pentathlon team.

BCA Spring Meeting 2012

Apr 202012

The 2012 Meeting of the British Crystallographic Association was held at Warwick University. Oxford was very well represented this year with Kirsten Christensen chairing the Programme Committee and prizes being awarded to Joe Paddison, Nick Funnell and Emma McKinley.

Other contributions from Oxford include:

Karim J. Sutton, Kirsten E. Christensen, Amber L. Thompson & Richard I. Cooper
Exploiting the Tunable Wavelength Capabilities of I19 (Poster & Oral Presentation)

Callum A. Young & Andrew L. Goodwin
An Examination of the Low Temperature Structure of Fe₃O₄ Using Reverse Monte Carlo Refinements (Oral Presentation)

Andrew L. Goodwin
Frameworks, Flexibility and Frustration (Oral Presentation)

Kirsten E. Christensen, Amber L. Thompson & Arwen R Pearson
Discussion Forum: From Small Molecules to Proteins: Bridging the Gap

Emma J. McKinley, Kirsten E. Christensen & Amber L. Thompson
Investigation of the Transient Modulated Phase of Barluenga’s Reagent (Poster)

Andrew B. Cairns, Amber L. Thompson, Andrew L, Goodwin, Matthew G. Tucker & Julien Haines
Anomalous Compression of Cyanide Frameworks: Mechanisms for Extreme Negative Response (Poster)

Callum A. Young, Edward Dixon, Michael A. Hayward & Andrew L. Goodwin
Apical Oxygen Bonding in YBCO – A Reverse Monte Carlo Approach (Poster)

Ines E. Collings, Andrew B. Cairns, Amber L. Thompson, Andrew L, Goodwin, Philip Pattison, Julien Haines, Matthew G. Tucker, Julia E. Parker & Chiu C. Tang
Transferable Mechanics in Molecular Framework Materials (Poster)

Joseph A. M. Paddison, Andrew L. Goodwin, Ross Stewart, Pascal Manuel, Matthias J. Gutmann, David A. Keen, Matthew G. Tucker, Andrew Wildes & Brian Rainford
Frustration and Magnetic Diffuse Scattering in β-Mn_0.8Co_0.2 and MnO: A Reverse Monte Carlo Study (Poster)

Matthew Cliffe & Andrew L. Goodwin
Disorder and Defects in Zirconium MOFs (Poster)

Nicholas P. Funnell, Martin T. Dove Andrew L. Goodwin Simon Parsons & Matthew G. Tucker
How Molecules Prepare to Undergo a Transition: The Onset of Disorder in Solid Cyclohexane (Poster).

Karim speaks to the Young Crystallographers

Emma, Richard and Ines go to the conference dinner

Ines and Emma

This time Karim brought his Dad…

Callum and Emma at Dinner

Kirsten presents Nick with his prize

Emma receives her prize

Contemplating Fourier Transforms…

Alkyl-chain Disorder in Tetraisohexylammonium Bromide

Mar 192012

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, both on general positions. At 100 K, the ammonium cation exhibits one ordered isohexyl chain and three disordered isohexyl chains. At 250 K, all four isohexyl chains are disordered. In an effort to reduce the disorder in the alkyl chains, the crystal was thermally cycled, but the disorder remained, indicating that it is dynamic in nature.

Tetraisohexylammonium Bromide

Electronic reprints

Oxford University Research Archive [direct pdf]

Publisher’s copy

IUCr

Dr. David R. Allan

Mar 072012

Dave is the Principal Beamline Scientist on the small-molecule single-crystal diffraction beamline, I19. Before his appointment at Diamond in 2006, Dave was a lecturer in The School of Physics at The University of Edinburgh and he laterally held an EPSRC Advanced Research Fellowship within The School of Chemistry. Apart from developing the beamline to improve its capabilities for the ever increasing user base, his main research interests involve the high-pressure and low-temperature polymorphism of small-molecule systems and the development of in situ crystal growth techniques. Dave can occasionally been seen around the department, usually on Tuesdays, when he gets the chance to attend the Chem. Cryst. group meetings.

Miss Emma J. McKinley

Feb 082012

Emma completed her Part II in 2011 in Chem. Cryst., but it seems we can’t get rid of her! Ever cheerful, she brings a spark of life to the lab and has come back for a bit to encourage us to write up the outstanding papers from her thesis, in particular her work chalcones and on the modulated phase of Barluenga’s reagent. Since her prize winning poetry performance at the BCA, we keep expecting her to start rapping…

Structure of the Month – September 2011

Sep 012011

Presented by: Andrew B. Cairns & Dr. Amber L. Thompson
Research Leader: Dr. Andrew L. Goodwin
Published: Journal of the American Chemical Society (cover article)

Negative Linear Compressibility (NLC) is where a material unusually expands in one direction under increasing pressure. Potassium manganese dicyanoargentate exhibits the largest NLC over an extended range of any known material: ‑12.0(8) TPa^–1. The structural features are both beautiful and unique to cause this effect. [MnN₆] octahedra are connected via almost linear ‘floppy’ NC–Ag–CN units, with K⁺ ions positioned above and below alternating Ag₃ Kagome triangles (top). The lattice framework is made up of three independent interpenetrated a-Polonium nets (bottom right), with only weak argentophilic interactions between the nets. Variable temperature SCXRD was carried out in Oxford and the variable pressure work was the first pressure experiment carried out on WISH at ISIS.

Structure of the Month – September 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.

Structure of the Month – December 2010

Dec 012010

Presented by: Dr. Adrian B. Chaplin
Research Leader: Prof. Andrew S. Weller
Published: Journal of the American Chemical Society

Making and breaking C–C bonds in the solid state: The structure of [Ir(BINOR‑S)(PiPr₃)][BAr^F₄] over the temperature range 100–250 K reveals a dynamic equilibrium between Ir(III) C–C agostic and Ir(V) bis-alkyl tautomers in the solid-state. The solid-state dynamic behaviour is shown in the reaction scheme (a), with populations determined using X-ray diffraction (b) and the Van’t Hoff plot for this process (c, R2(fit) = 0.999).The disordered model at 150 K containing (d) Ir(III) and (e) Ir(V). The combined model and thermal ellipsoid plot of the structure refined without cation disorder modelling are also shown (f & g respectively).

Structure of the Month – December 2010

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