In the solid state, the environment around a hydrogen bond is known to alter the behaviour of the proton, leading to effects such as proton disorder or migration across bonds as a function of temperature. However, it is difficult to control and predict when this may happen. 4-dimethylaminobenzoic acid (4DABA) contains dimeric building blocks in its pure form and also exhibits hydrogen disorder.However, introducing the second component 3,5-dinitrobenzoic acid into the crystalline lattice removes this disorder within the 4DABA unit. Using SXD at ISIS, we have shown that introducing a third component, 4,4'-bipyridine, further perturbs the local environment, and hydrogen disorder is again observed. These results show that the behaviour of hydrogen atoms can be tuned by modifying the molecular and crystalline environment around the 4DABA dimer building block, with implications for the general control of proton transfer processes.
LH Thomas, AA Kallay, A Parkin, CC Wilson (Glasgow and Bath Universities), N Blagden (Bradford University), CC Seaton (Manchester University), MJ Gutmann (ISIS)
Research date: January 2010
Contact: Prof CC Wilson, C.C.Wilson@bath.ac.uk
Further reading: LH Thomas et al., Cryst Growth Design 10 (2010) 2770