Inclusion Compounds of Tetrakis(4-nitrophenyl)methane: C−H···O Networks, Pseudopolymorphism, and Structural Transformations

Tetrakis(4-nitrophenyl)methane is a new host material with considerable structural adaptability over
a range of solvents. The crystal structures of 14 of these solvates have been determined and classified into
three groups. The diamondoid group, wherein the host molecules form a 2-fold interpenetrated diamondoid
network structure, is unprecedented in that network connections are made exclusively with weak C−H···O
and π···π interactions. This group consists of the solvates of THF, dioxane, nitrobenzene, 4-bromoanisole,
anisole, phenetole, p-xylene, and chlorobenzene. The rhombohedral group, which is characterized by specific
host···guest interactions of the C−H···O and halogen···O2N type, consists of the solvates of CHCl3 and CHBr3
and somewhat surprisingly DMF, which shows an unusual 3-fold disorder mimicking in part the shape and
size of the haloform molecules though not their orientation. The third group comprises solvent-rich solvates
of the host with mesitylene, collidine, and o-xylene with quite different crystal structures. The THF solvate
was found to lose solvent over limited temperature ranges transforming reversibly from the diamondoid structure
to the rhombohedral structure. A mechanism for this process is outlined. Material from which solvent has
been removed by heating was also found to resolvate upon soaking in appropriate solvents. In summary, the
title compound forms a host network that is partially robust and in part flexible. It is possible that this fluxional
nature of the host network derives from the weakness of the connecting interactions.