Molecular recognition among alcohols and amines: super-tetrahedral crystal architectures of linear diphenol–diamine complexes and aminophenols
Hydroxy and amino groups are complementary as regards hydrogen-bond donors and acceptors. This is expected to lead to molecular recognition among alcohols and primary amines, i.e., to a propensity towards formation of 1 : 1 alcohol–amine complexes, driven by a 50% increase of the number of hydrogen bonds as compared with the uncomplexed constituents. Possible hydrogen-bonded architectures of such complexes are suggested, and the concept is successfully exploited for crystal engineering purposes by drawing upon linear diphenols, aromatic diamines, and aminophenols as supramolecular partners. Specifically, the crystal-structural chemistry is reported of the 1 : 1 molecular complexes between hydroquinone and p-phenylenediamine, hydroquinone and benzidine, 4,4′-dihydroxybiphenyl and p-phenylenediamine, 4,4′-dihydroxybiphenyl and benzidine, as well as of p-aminophenol, and of 4,4′-hydroxyaminobiphenyl. The diphenol–diamine complexes form hyderogen-bonded super-diamond lattices with 1.5 O(H) N bonds per oxygen and nitrogen atoms, respectively. Again exclusively via O(H)N bonds, the aminophenol structures are also supertetrahedral but after the manner of the polar wurtzite variant. Some similar reported structures are analysed in the light of the present concepts and results, and implications are discussed of the finding that molecular recognition is possible among molecules as standard as simple alcohols and amines.