The lowest energy crystal structure (1) in the 0.85 g/cm 3 spike features hexagonal arranged networks of hydrogen bonded TMA molecules, as in  and -TMA. Importantly, these hexagonal nets are planar and aligned in the crystal structure, in contrast to previously reported TMA solvate structures that feature offset arrangements of hexagonal TMA nets. Other low energy structures in this spike are very similar, but differ in conformation of TMA within the hexagonal sheets, distortion of the hexagonal pores or breaking of the hydrogen bonded hexagons to form hydrogen bond interactions between layers of TMA. Hexagonal pores in the 1.1 g/cm 3 predicted structure, 2, are collapsed in one direction of the hydrogen bonded sheets (Figure ), forming a structure that is intermediate between the open hexagonal sheets and the 'flower' monolayers sometimes seen at liquid-substrate interfaces. As in predicted structure 1, the remaining hexagonal pores in 2 are aligned, forming open channels.