The properties of solids depend critically on structure. Some materials can crystallise in more than one structural form, a phenomenon referred to as polymorphism. Some very simple molecular systems are highly polymorphic: water for example has 19 solid forms, and research to find more is still being carried out. Formamide is the simplest amide, with formula H2NCH=O. It has recently been implicated in the photocatalytic formation of nucleoside bases, and it may have been a precursor to biological compounds required for life. Upon cooling, formamide crystallises into a structure which remains essentially unchanged down to 2K, and until recently this was the only crystalline form of formamide known. Following recent neutron diffraction experiments on PEARL, we have shown that formamide forms no fewer than four different polymorphs at room-temperature and pressures between 0.1 and 3GPa. The structures can be understood in terms of the different conformations of hydrogen-bonded chains of molecules, and the ways in which these chains interact.
A Dawson, LE Budd, S Parsons (University of Edinburgh), WG Marshall (ISIS)
Research date: December 2006
Dr S Parsons, [email@example.com] SA Moggach et al., Acta Cryst. B62 (2006, In press)