There is an upsurge of interest in contemporary theoretical and experimental research to unravel the structural details of water clusters. [1±8] The clusters are believed to be the perfect means for characterizing the structural changes and bonding mechanisms in passing from isolated molecules to a macroscopic collection, namely, bulk water, whose anomalous properties still remain mysteries. [1, 2, 9] A variety of modern theoretical and experimental methods have been employed to characterize the clusters. Both experiment and theory strongly suggest that the water trimer, tetramer, and pentamer have cyclic and quasiplanar minimum-energy structures. The larger clusters are expected to have 3D geometries, with the hexamer behaving as the transition from 2D to 3D structures. [1, 2] The X-ray structural characterization of a decamer [10] and an octamer water cluster (cubic [11] and cyclic [12] forms) have been reported recently. Theoretical calculations for the hexamer have revealed the existence of several energy minima corresponding to ™ring∫, ™book∫, ™bag∫, ™cage∫, and ™prism∫ topologies within 0.7 kcal mol À1 . [13±15] The lowest energy conformer is the ™cage∫ followed by the ™book∫ and ™prism∫ structures, which are less than 0.1 and 0.2 kcal mol À1 higher in energy, respectively. [13±15] The ™ring∫ and ™bag∫ structures have been shown to be 0.5 and 0.7 kcal mol À1 higher in energy than the ™cage∫. To date, ™chair∫ [16,17] and ™boat∫ [18] cyclic hexamers included in host lattices have been characterized by X-ray crystallographic analysis. While Saykally and co-workers characterized the cage form of the hexamer, [15] Nauta and Miller reported the detection of a ™quasiplanar∫ hexamer in a helium droplet. [19] Herein, we report the first Xray structural characterization of the high-energy cyclic form of the water hexamer trapped in an organic supramolecular complex with the bimesityl dicarboxylic acid 4. The planar ring constitutes the basic structural motif of the high-pressure Ice II modification, [20] and is also one of the prominent morphologies found in the computer simulation of liquid water. [21