Systematic studies of crystal structures under non-ambient conditions

Abstract

Variable temperature single crystal X-ray diffraction analysis has been used to study four molecular systems: 4-(p-trlfluoromethyl phenylethynyl) prefluorotoluene (1), 2-methyl-4-(4-trifluoromethyl-phenyl) but-3-yn-2-ol (2), phenylethynyl perfluorotoluene (3) and Zinc Pyromellitate. In the case of the systems (1) - (3), the aim was to analyse the extent of the dynamic disorder in the CF3 groups that are contained in these systems. To this end, segmented rigid body analysis has been employed to estimate forces constants and barriers to rotation of the relevant groups. Complimentary computational methods have been used to obtain further estimates of this barrier to rotation in these systems for both the isolated (gas phase) molecules and for the condensed matter phases for compounds (1) and (3).For Zinc Pyromellitate, variable temperature single crystal X-ray and neutron analysis have been used to probe the behaviour of a proton that sits in a short, strong intramolecular hydrogen bond. The aim here was to discover whether the system exhibits proton migration along the hydrogen bond as a function of temperature and thus gain insights into the energy potential well in which the proton sits. To this end, both computational methods have been used to study the pyromellitate fragment, and variable temperature full crystal structure data so as to gain direct access to information regarding this potential well.