Stable heterotopic noncovalent resorcin[4]arene assemblies

Resorcin[4]arene tetracarboxylic acids 5,6 (A) and resorcin[4]arene tetrapyridines 2,3 (P) self-assemble in chloroform solution to form stable heterotopic AP dimers. Data from NMR titration and dilution experiments, as well as from vapor-pressure osmometry (VPO), indicate that the AP dimer is formed with an association constant greater than 10⁷ M^-1. Solid-solution extraction experiments are indicative of the formation of a 2:1 trimer (A₂P), while self-associated homotopic species (A₂ and A₃) can be detected by NMR and VPO. Analysis of the heterotopic noncovalent assembly process over a range of compositions shows that these other species are much less stable than the AP heterodimer, which is the exclusive species at an A/P concentration ratio of 1:1 (> 99.7% of the total at 10 mM).