known 5-fold crystal structure). This falls within the usual energetic range of polymorphism in organic crystals, and we expected therefore that this structure should be accessible under the right crystallization con-ditionA large number of predicted structures with 3fold interpenetrated diamondoid hydrogen bonded networks are found in the region around 1 g/cm 3 (cluster of green points in Fig. ). The many possibilities for 3fold interpenetration, compared to higher and lower degrees of interpenetration, can be rationalized by the number of available permutations for arriving at 3-fold interpenetrated structures by the removal of 2 networks from the 5-fold interpenetrated structure.