A self-assembled fluoride-water cyclic cluster of [F(H2O)]4(4-) in a molecular box.

We present an unprecedented fluoride-water cyclic cluster of [F(H(2)O)](4)(4-) assembled in a cuboid molecular box formed by two large macrocycles. Structural characterization reveals that [F(H(2)O)](4)(4-) is assembled by strong H-bonding interactions [OH···F = 2.684(3)-2.724(3) Å], 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 (19)F NMR and (1)H 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.