A Self-Assembled Fluoride-Water Cyclic Cluster of [F(H2O)]44- in a Molecular Box

We present an unprecedented fluoride-water cyclic cluster of [F(H2O)](4)(4-) assembled in a cuboid molecular box formed by two large macrocycles. Structural characterization reveals that [F(H2O)](4)(4-) is assembled by strong H-bonding interactions [OH center dot center dot center dot F = 2.684(3)-2.724(3) angstrom], where a fluoride anion plays the topological role of a water molecule in the classical cyclic water octamer. The interaction of fluoride was further confirmed by F-19 NMR and H-1 NMR spectroscopies, indicating the encapsulation of the anionic species within the cavity in solution. High-level DFT calculations and Bader topological analyses fully support the crystallographic results, demonstrating that the bonding arrangement in the fluoride-water cluster arises from the unique geometry of the host.