Sep 232016
 

Journal of the American Chemical Society 2016, 138(40), 13314-13325 [doi:10.1021/jacs.6b07501]

Hydrogen bonding with fluoride is a key interaction encountered when analyzing the mode of action of 5′-‚Äčfluoro-‚Äč5′-‚Äčdeoxyadenosine synthase, the only known enzyme capable of catalyzing the formation of a C-‚ÄčF bond from F‚Äč. Further understanding of the effect of hydrogen bonding on the structure and reactivity of complexed fluoride is therefore important for catalysis and numerous other applications, such as anion supramol. chem. Herein we disclose a detailed study examg. the structure of 18 novel urea-‚Äčfluoride complexes in the solid state, by X-‚Äčray and neutron diffraction, and in soln. phase and explore the reactivity of these complexes as a fluoride source in SN2 chem. Exptl. data show that the structure, coordination strength, and reactivity of the urea-‚Äčfluoride complexes are tunable by modifying substituents on the urea receptor. Hammett anal. of aryl groups on the urea indicates that fluoride binding is dependent on ŌÉp and ŌÉm parameters with stronger binding being obsd. for electron-‚Äčdeficient urea ligands. For the first time, defined urea-‚Äčfluoride complexes are used as fluoride-‚Äčbinding reagents for the nucleophilic substitution of a model alkyl bromide. The reaction is slower in comparison with known alc.-‚Äčfluoride complexes, but SN2 is largely favored over E2, at a ratio surpassing all hydrogen-‚Äčbonded complexes documented in the literature for the model alkyl bromide employed. Increased second-‚Äčorder rate consts. at higher diln. support the hypothesis that the reactive species is a 1:1 urea-‚Äčfluoride complex of type [UF]‚Äč (U = urea) resulting from partial dissocn. of the parent compd. [U2F]‚Äč‚Äč. The dissocn. processes can be quantified through a combination of UV and NMR assays, including DOSY and HOESY analyses that illuminate the complexation state and H-‚Äčbonding in soln.

Fluoride‚Äďurea complex

Publisher’s copy

Jun 232015
 

Fluoride‚Äďalcohol complexChemical Science 2015, 6, 5293-5302
[doi:10.1039/c5sc01812a]

The nucleophilic reactivity of fluoride ion is altered in the presence of hydrogen-bond donors, including alcohols. Relatively little is known about the coordination involved; to rectify this, the X-ray structures of fourteen novel fluoride‚Äďalcohol complexes with tetrabutylammonium as the counterion have been determined. The coordination number varies from two to four depending on the steric bulk of the alcohol and is closely linked to trends in reactivity. This diversity in coordination stoichiometry is unprecedented but significant, as it implies differences in the ability of the fluoride-alcohol complexes to dissociate in solution with release of a more active and/or selective fluoride source.

Publisher’s copy

Nov 042014
 

CrystEngComm (2015) 17, 1927-1934 [ doi:10.1039/C4CE01912A ]

heatmapMachine learning algorithms can be used to create models which separate molecular materials which will form good-quality crystals from those that will not, and predict how synthetic modifications will change the crystallinity.

Chemistry World Article: Will It Crystallise

Publisher’s copy

 

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‚ÄĎray 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 ‚Äúice-rules‚ÄĚ that establish a mapping between the dynamics of Cd(CN)2and proton ordering in cubic ice VII.

Structure of the Month ‚Äď November 2012

Structure of the Month ‚Äď November 2012

 

Oct 102012
 

Mr. George W. Pidgeon

George is working on a collaborative project with Prof. V√©ronique Gouverneur’s Research Group to study the effect of hydrogen bonding on the nucleophilicity and basicity of tetra alkyl ammononium fluoride complexes.¬† When he‚Äôs not praying for his products to crystallise, George spends his time running the Oxford University Darts Club and playing the trombone for the Oxford University jazz orchestra.