Bringing a Molecular Plus One: Synergistic Binding Creates Guest-Mediated Three-Component Complexes.

C-2-methylresorcinarene (), pyridine (), and a set of 10 carboxylic acids () associate to form ternary assemblies with 1:1:1 stoichiometry, representing a useful class of ternary systems where the guest mediates complex formation between the host and a third component. Although individually weak in solution, the combined strength of the multiple noncovalent interactions organizes the complexes even in a highly hydrogen-bond competing methanol solution, as explored by both experimental and computational methods. The interactions between and are dependent on the p values of carboxylic acids. The weak interactions between and further reinforce the interactions between and , demonstrating positive cooperativity. Our results reveal that the two-component system such as that formed by and can form the basis for the development of specific sensors for the molecular recognition of carboxylic acids.