Characterization of a Planar Cyclic Form of Water Hexamer in an Organic Supramolecular Complex: An Unusual Self-Assembly of Bimesityl-3,3′-Dicarboxylic Acid

Abstract

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] COMMUNICATIONS

Structures of an infinite helical water chain and discrete lattice water in metal–organic framework structures

“…Unfortunately, the structural analysis reveals that no water cluster is found in 2, maybe due to the alteration of the central ion, leading to the formation of the different environment and vice versa. As is known, the degree of structuring of the water cluster that can be imposed by its environment, and vice versa, can also be of importance in the design of new MOFs [26][27][28][29][30]. Here, both water-MOF and water-water interactions can be important for the stability of the overall structure.…”

Supramolecularly assembled water layers stabilized by sebacic anions in complexes of Zn(II) and Co(II)

“…For chemical and biochemical reasons, experimental [1][2][3][4][5][6][7][8][9][10] and theoretical [11,12] studies of water clusters have been of much interest. Water clusters of different nuclearities have been observed in crystal hydrates of organic and metal-organic compounds.…”

“…Water clusters of different nuclearities have been observed in crystal hydrates of organic and metal-organic compounds. In most of the reported examples, basic units of a small number of water molecules are interconnected with each other to generate infinite polymeric networks such as chains [1], tapes [2], and 2D layers [3,4].…”

Structure and stability of spiro-cyclic water clusters

“…9,34 It is well-known from the crystal structure database that the water molecule plays different roles in the stabilization of crystal structures and displays a variety of structural topologies in crystal structures and in confined environments. [35][36][37][38][39][40][41][42] The surge in activity in the area of supramolecular chemistry exemplifies the importance of water mediated crystallization and H-bonding interaction.…”