Molecular Recognition by Halogen Bonding With Atomic Precision in a Covalent Organic Cage

Halogen bonding (XB) is a recognition motif of increasing importance but it remains underused in solution. Embedding a single XB motif within a molecular capsule improves both its stability and interaction strength by finely tuning inward position and orientation. In this context, a new Covalent Organic Cage (COC) was prepared sequestering a polarized P-Cl bond. This hemicryptophane carrying a haloazaphosphatrane moiety was found to bind dimethyl methylphosphonate (DMMP), a Sarin surrogate, by halogen bonding with atomic precision. Indeed, the same cage having the chlorine atom substituted by a hydrogen atom showed no detectable recognition. Such level of discrimination definitely establishes halogen bonding COC as a new generation of efficient receptors for molecular recognition.