We describe the ion pair-driven heterodimeric capsule formation of a cyclotricatechylene 1 and a boronic acid-appended hexahomotrioxacalix[3]arene 2. Although I does not interact with 2 in a protic solution, in the presence of Et4NAcO quantitative formation of a heterodimeric capsule via boronate esterification was observed in the NMR, a direct result of anion-induced boronate ester formation and the Et4N+ template. Reversible boronate esterification allowed us to selectively control capsule assembly using pH switching.