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

A series of compounds with multiple PhNH 2 groups were synthesized and crystallized, and their structures were solved by X-ray diffraction to assess the ability of -NH 2 groups in anilines to direct molecular crystallization. 2,2‘,7,7‘-Tetraamino-9,9‘-spirobi[9 H -fluorene] ( 1c ) forms an inclusion complex held together in part by donation of hydrogen bonds from -NH 2 groups to guest molecules. Surprisingly, the -NH 2 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 -NH 2 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 -NH 2 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.