The disorder arises because the hydrogen of the thiol group can form a hydrogen bond with either another thiol group (as in the Form I 30 K crystal structure) or with an oxygen of the carboxylate anion as shown in Figure . In the neutron diffraction results at room temperature the C-C-S-H dihedral angle (τ ) was reported to be 77.6 • and -85.4 • for the SH...S and SH...O H-bond interactions respectively. In an X-ray and a polarised Raman study of single crystals of Form I over a range of temperatures from 3 K to 300 K 6 the transition between the ordered, low temperature structure and the disordered room temperature structures took place via a series of stages involving activation of the motion of different groups at different temperatures. These results explained the observation of an extended transition observed by calorimetry around 70 K and also explained why the heat capacity is sensitive to the thermal history. Heat capacities of Form I 8 showed that there is actually a sharp transition at 76 K consistent with an ordering transition of the thiol groups. In order to model the data it was necessary to use a two level model; a Debye model for the acoustic phonons and an Einstein model for the optical phonons. The Einstein model is normally used for localised cage phonons and was thought in this case to represent the motion of water molecules trapped in the lattice. The boson peak which is seen in the low frequency Raman spectrum of Form I 9 can also be explained as the result of a glassy form of disorder in the water molecules distribution.