Crystal chemistry of tetraradial species. Part 4. Hydrogen bonding to aromatic π systems: crystal structures of fifteen tetraphenylborates with organic ammonium cations

The aim of this investigation is to provide a classification and examples of N—H …π (and also O—H …π) bonds to the aromatic π systems in organic ammonium tetraphenylborates that would serve as reference for X—H …π(arene) bonds in general. To this end the crystal structures of the tetraphenylborates of the following cations have been determined: Me3NH+, Et3NH+, quinuclidinium, DabcoH+, Et(iso-Pr)2NH+ (monohydrate), (Ph3B)NH[—(CH2)2—]2NHMe+ (Me2CO solvate), Me2NH2+ (MeCN and Et2CO solvates), Et2NH2+, (iso-Pr)2NH2+, azoniacycloheptane, guanidinium (monohydrate), MeNH3+, EtNH3+, and 1-adamantammonium (monohydrate). These structures contain a variety of normal, bifurcated, and trifurcated N—H …π bonds as well as normal O—H …π bonds to the phenyl groups of the anion. The X—H …π bonds will form whenever opportunity arises, even though the result may be unfavourable bonding geometry. Branched bonds and orientational disorder represent compromise solutions in situations where the H(X) hydrogens are presented with ...