Figure 4.

Three types of octamers are shown. (a) Octamer ‘)(’, (b) octamer ‘()’ and (c) octamer ‘((’. Green and black lines represent twofold and fourfold rotational axes, respectively. Molecules from octamers in (a) and (b) are shown in grey and green, respectively. The octamer in (c) is at the interface of the the octamers in (a) and (b). The colours of the molecules correspond to the colours in the octamers in (a) and (b). The fourfold rotational axis is crystallographic, whereas the twofold axes are point symmetry operations relating to the molecules in the octamers in (a) and (b), but not that in (c). The two regions that are involved in the interactions between the tetramers are shown in blue (11-PATA-14) and red (85-YQTN-88).