Solid-State Complexes of Calix[4]arene Dihydroxyphosphonic Acid with Bipyridyl Ligands

The robustness of calix[4]arene dihydroxyphosphonic acid and its ubiquitous dimeric motif offers perspectives for predefined solid-state complexation with small molecules. In the current article, we describe the complex of calix[4]arene dihydroxyphosphonic acid with three different forms of bipyridyl ligand:  2,2‘-bipyridine, 4,4‘-bipyridine, and 1,2-bipyridylethane. A number of resemblances and differences in the interactions between the components in the complexes are pointed out. All the complexes are based on layers of calixarene dimers alternated with layers of bipyridyl molecules. While the complex with 2,2‘-bipyridine is encaged by a dense network of hydrogen bonds, the complexes with 4,4‘-bipyridine and 1,2-bipyridylethane generate an extended 1-D ladder network. All of the complexes present π−π interactions between the bipyridyl moieties and the calix[4]arene dihydroxyphosphonic acid.