Molecular Tectonics. Hydrogen-Bonded Networks Built from Tetra- and Hexaanilines

A series of compounds with multiple PhNH2 groups were synthesized and crystallized, and their
structures were solved by X-ray diffraction to assess the ability of -NH2 groups in anilines to direct molecular
crystallization. 2,2‘,7,7‘-Tetraamino-9,9‘-spirobi[9H-fluorene] (1c) forms an inclusion complex held together in part
by donation of hydrogen bonds from -NH2 groups to guest molecules. Surprisingly, the -NH2 groups do not engage
in hydrogen bonding with each other. Tetrakis(4-aminophenyl)methane (2c) crystallizes to form a guest-free close-packed diamondoid network in which each -NH2 group donates and accepts one N−H···N hydrogen bond. Tetrakis[(4-aminophenoxy)methyl]methane (3c), a more flexible analogue, also crystallizes as a close-packed structure
maintained by an extensive network of N−H···N hydrogen bonds. Despite the structural similarity of tetraanilines
2c and 3c, their hydrogen-bonding patterns and network topologies are different. A flexible hexaaniline, 1,1‘-oxybis[3-(4-aminophenoxy)-2,2-bis[(4-aminophenoxy)methyl]]propane (4c), produces a close-packed network joined by both
N−H···N and N−H···O hydrogen bonds. Tetrakis(4-aminophenyl)ethylene (5) crystallizes as a hydrate to yield a
structure consisting of layered hydrogen-bonded sheets. The diverse hydrogen-bonding motifs observed show that
crystal engineering using direct interactions of the -NH2 group of anilines is a challenging endeavor, and other
intermolecular interactions can compete effectively with N−H···N hydrogen bonds to determine how crystallization
occurs.