Molecular Tectonics. Construction of Porous Hydrogen-Bonded Networks from Bisketals of Pentaerythritol

2,4,8,10-Tetraoxaspiro[5,5]undecanes tetrasubstituted at the 3 and 9 positions with groups
incorporating diaminotriazines can be used for the construction of extensively hydrogen-bonded
networks by the strategy of molecular tectonics. Four such compounds, tectons 1−4, were made by
short and efficient syntheses involving bisketalization of pentaerythritol and subsequent reactions.
Unlike tectons typically used in previous studies, compounds 1−4 are flexible and chiral, and they
orient four sticky diaminotriazine groups in a distorted tetrahedral geometry. Tecton 1 crystallizes
from DMF/toluene as an inclusion compound of approximate composition 1·8DMF·xH2O. In the
resulting structure, each tecton participates in a total of 16 hydrogen bonds. Eight of these bonds
involve four principal neighbors, and the tectons linked in this way define a distorted diamondoid
network. Despite 8-fold interpenetration, 60% of the volume of the network is available for including
guests. The guests are disordered and occupy parallel helical channels that have cross sections of
approximately 11 × 12 Å2 at the narrowest points. These channels provide access to the interior of
the crystals and permit guests to be exchanged quantitatively without loss of crystallinity. It is
noteworthy that tecton 1, despite its flexibility, small size, and structural simplicity, is apparently
unable to find a periodic three-dimensional structure in which the dictates of hydrogen bonding
and close packing are satisfied simultaneously.