The same diamondoid hydrogen bonding, but with lower degrees of interpenetration, is found in many of the other predicted structures towards lower crystal densities and higher lattice energies. Figure highlights these structures, with different colors indicating the number of unique hydrogen-bond networks interpenetrated within each structure. While most of these structures occur within the bulk of the energy-density distribution of structures, the most stable predicted structures for each degree of interpenetration, from 5fold ( = 1.57 g/cm 3 ) down to 2-fold ( = 0.324 g/cm 3 ) interpenetration, lie just below the low-energy 'leading edge' of the energy-density distribution. These structures corresponding to the lowest energy instances of each level of interpenetration are found at approximately equally-spaced intervals of density and they lose, on average, around 20 kJ/mol of lattice energy per lost degree of interpenetration of the hydrogen bonding networks (Figure ). The energetic stability of these diamondoid hydrogen-bonded structures relative to other crystal packing arrangements is not as pronounced as the 'spike' of structures containing the new  polymorph, 1, on the TMA landscape (Fig. ). However, this double hydrogen bonding motif clearly provides greater stability than any other hypothetical crystal packing of similar density in the cases of 3-fold, 4-fold and 5-fold interpenetration.