Structure of the Month – Chemical Crystallography

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

Structure of the Month – September 2012

Sep 042012

Presented by: Sebastian D. Pike & Dr. Amber L. Thompson
Research Leader: Prof. Andrew S. Weller
Published: Science

Transition metal σ-alkane complexes are key intermediates in catalytic C–H activation processes. We have used a direct crystal to crystal transition, by reaction with H₂, to produce an alkane σ-complex directly. This structure is of an alkane (norbornane, NBA) σ-bound to a d⁸–Rh(I) metal centre, in which the chelating alkane ligand is coordinated to the pseudo-square planar metal centre through two σ-C–H bonds. Although disordered (inset), the structure was refined without restraints for the coordinated NBA. The complex reacts further over time, so many attempts were required to “catch” the crystal free from both starting material and final product.

Structure of the Month – September 2012

Structure of the Month – May 2012

May 012012

Presented by: Nicholas G. White
Research Leader: Prof. Paul D. Beer
Published: Chemical Communications

Pyridinium-3,5-bis(triazole) can bind anions through polarised C-H···anion hydrogen bonds. We have incorporated this motif into pseudorotaxanes, catenanes and rotaxanes (in conjunction with an isophthalamide macrocycle), and the resulting interlocked architectures are formed in high yields and display interesting and unusual anion selectivities. Despite the difficulties of crystallising such systems, single crystals of a pseudorotaxane, rotaxane and catenane have all been isolated (as chloride salts). Data were collected using a Nonius Kappa-CCD, synchrotron radiation on I19 at Diamond and Cu Kα radiation with an Oxford Diffraction (Agilent) SuperNova (respectively). All three datasets are of unusually high quality for such systems (final R1 [I > 2σ(I)] = 6.9-8.0%).

Structure of the Month – May 2012

Structure of the Month – January 2012

Jan 012012

Presented by: Dr. Andrew D. Schwarz
Research Leader: Prof. Philip Mountford
Published: Chemical Science

Inspired by the development of high-energy, early transition metal-ligand multiply-bonded systems, we targeted the unprecedented classes of bis(imido) and tris(imido) compounds of the group 4 metals (to give the first example of a group 4 metal simultaneously containing two or three multiply-bonded ligands). The product above was prepared by deprotonation with methyl lithium of a mono(imido) bis(amido) sython [Ti(NAr)(NHAr)₂(py)₂] to form the supposed intermediate “Li₂[Ti(NAr)₃(py)_x]” which undergoes 1,2-N–H addition of ArNH₂ across one of the Ti‑NAr linkages. This represents the first bis(imido) complex of a group 4 metal, and indeed the first example of any compound of these metals simultaneously containing two or more metal-ligand multiple bonds to dianionic ligands.

Structure of the Month - January 2012

Structure of the Month – November 2011

Nov 012011

Presented by: Matthew P.Blake
Research Leader: Prof. Philip Mountford
Published: Journal of the American Chemical Society

Metal-metal bonded molecular compounds have been an essential part of development in inorganic chemistry for decades; research has been reenergized by the discovery of the first Cr-Cr quintuple-, Zn-Zn single- and Mg-Mg single bonds. However, within this rich and topical area, there remains very little experimental or theoretical information regarding bonds between alkaline earth elements and transition metals. While bonds between calcium and main group metals (Ga, Sn) have been reported, the bonding of calcium with a transition metal had not been studied. Reaction of calcium amalgam with [CpFe(CO)₂]₂ (Fp₂) gave the alkaline earth compound [CaFp₂(THF)₃]₂containing two direct Ca–Fe (3.0185(6) Å) bonds.

Structure of the Month - November 2011

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

Structure of the Month – June 2011

Jun 012011

Presented by: Matthew J. Langton, Jonathan D. Matichak & Dr. Amber L. Thompson
Research Leader: Prof. Harry L. Anderson
Published: Chemical Science (cover article)

Fully π-conjugated porphyrin oligomers exhibit remarkable properties such as ultrafast energy migration, strong two-photon absorption and wire-like charge transport. The possibility to encapsulate them by rotaxane formation may provide valuable control over their properties by offering a unique approach to engineering intermolecular interactions. An active-template Cu-mediated Glaser coupling provides an efficient route to these structures. Data from crystals of this rotaxane were collected in-house. The porphyrin dimer is slightly twisted and non-linear, contrasting with previously reported structures which possess an inversion centre (and are thus rigorously planar). The phenanthroline units of the threaded macrocycle form tightly packed π-stacks in the crystal.

Structure of the Month – June 2011

Structure of the Month – May 2011

May 012011

Presented by: Matthew Tatton & Paul Winship
Research Leader: Prof. Timothy J. Donohoe
Published: Angewandte Chemie International Edition

This is the final isolated intermediate in the synthesis of Neodysiherbaine A; crystals were very small, so data were collected on I19 at Diamond. The natural product is an excitatory amino acid isolated from the Dysidea herbacea Micronesian sponge by Sakai et al. Biological studies have shown that (–)-neodysiherbaine A is a potent convulsant and is a highly selective agonist for KA and AMPA glutamate receptors. (–)-neodysiherbaine A was a target as part of a research programme to develop new catalytic methods for the formation of heterocycles. Our retrosynthesis of this led to the disconnection of the central THF ring back to a hydroxyl alkene as a precursor for our recently developed Lewis acid catalysed oxidative cyclisation.

Structure of the Month - May 2010

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 – February 2011

Feb 012011

Presented by: Dr. Andrew D. Schwarz & Liban M. A. Saleh
Research Leader: Prof. Philip Mountford & Prof. Simon Aldridge
Published: Journal of the American Chemical Society

Transition-metal boryl compounds (L)M(BX₂)_x, containing 2‑center, 2‑electron σ‑bonds have been a topic of outstanding interest due to pivotal roles in a variety of catalytic and stoichiometric transformations, e.g. hydroboration and diboration of C–C π-bonds, and functionalization of alkane and arene C‑H bonds. To date, virtually all boryl complexes have been prepared either by B‑X (X = H or halogen) or B‑B oxidative addition to a low oxidation state (L)M species, or by nucleophilic attack of a [(L)M]‑ anion on a XBR₂ or related source of the boryl moiety. However, utilisation of the nucleophilic Li{B(NArCH)₂}(THF)₂ (Ar = 2,6‑C₆H₃ⁱPr₂), allows access to rare earth metal boryl compounds. Data were collected on a small colourless crystal (0.05 × 0.05 × 0.05 mm) using the new Oxford Diffraction (Agilent) SuperNova diffractometers and copper radiation.

Structure of the Month – February 2011

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