Recognition studies of a pyridine-pendant calix[4]arene with neutral molecules: Effects of non-covalent interactions on supramolecular structures and stabilities

A new calix[4]arene derivative containing hydrogen bond accepters, 5,11,17,23-tetra-tert-butyl-25,27-bis[(4- pyridylmethyl)oxy]-26,28-dihydroxycalix[4]arene (L), has been synthesized. H-1-NMR titrations in chloroform-d were carried out to investigate the host-guest chemistry of L towards neutral molecules containing a wide variety of hydrogen bond donor groups such as aldehyde derivatives of p-tert-butylcalix[4]arenes (compounds 3 and 4), acetylacetone, 1,2-diaminoethane, 2,6-diaminopyridine, catechol, resorcinol, hydroquinone, phthalic acid, isophthalic acid and terephthalic acid. L can form complexes with resorcinol, phthalic acid and catechol in 1:1 (log K = 3.13), 1:1 (log K = 5.41) and polymeric fashions, respectively. In addition, the solution structures of these complexes have been revealed by NOESY experiments. L forms a 1:1 complex with resorcinol by hydrogen bonding and van der Waals interactions resulting in a supramolecular framework. The phthalic acid molecule interacts with L via hydrogen bonding and is included into the lower rim cavity of L.