Crowned Tetrameric Spirocyclic Water Chain: An Unusual Building Block of a Supramolecular Metal-Organic Host Somnath Ray Choudhury, ² Atish Dipankar Jana,* ,§ Enrique Colacio, ‡ Hon Man Lee, ⊥ Golam Mostafa, § and Subrata Mukhopadhyay* ,² Department of Chemistry, JadaVpur UniVersity, Calcutta 700 032, India, Department of Physics, JadaVpur UniVersity, Calcutta 700 032, India, Departamento de Quı ´mica Inorga ´ nica, UniVersidad de Granada, 18071-Granada, Spain, Department of Chemistry, National Changhua UniVersity of Education, Changhua 50058, Taiwan ReceiVed NoVember 25, 2006 ABSTRACT: A 3D supramolecular metal-organic host could be realized in solid in which the water assembly as a whole acted as a building block of the 3D framework with rectangular channels where guest molecules reside, adding a new dimension to water cluster research where the role of water has been shifted from its usual behavior of guest to that of a host. The crystal structure of the compound, {[Cu(mal) 2 ](picH) 2 ‚5H 2 O} n , 1 [mal ) malonate dianion, picH ) protonated 2-amino-4-picoline], synthesized from purely aqueous media, shows that the Cu(II)-malonate 2D coordination polymeric sheets are locked together by the water assembly that lines up perpendicular to the Cu(II)-malonate sheets constituting a 3D infinite supramolecular host where within the channels protonated 2-amino-4-picoline auxiliary ligands are accommodated. A spirocyclic tetrameric water chain having a dimeric crown on it describes the composition of the water assembly that runs down the c-axis. Water, an elixir of life on our planet, is ubiquitous and covers two-thirds of the globe. However, a complete understanding of water’s behavior is still lacking, and the quest to understand water’s anomalous behavior continues. 1 The realization that condensed- phase behavior must be explained in terms of water clusters 2 led to the recent upsurge in water cluster research. Information on small water clusters in the gas phase was obtained through laser spectroscopic experiments, 3 supported by ab initio calculations. 4 Water’s ability to form flexible hydrogen bonds with its neighboring molecules has led to the detection of various ordered water assemblies 5-10 in various deformed geometries. 11 The key to understanding the behavior of water is the precise structural data of various hydrogen-bonded networks. One can now even think of engineering the water assembly inside organic and metal-organic frameworks (MOFs) in a systematic way by gradually tuning its environment and studying its effect on the hydrogen-bonded networks. 8b,12 An understanding of this mutual interaction, especially when the components of the framework resemble molecular building blocks in biology, can possibly unravel the role of ordered water in bio-environments. The water tetramer, one of the main cluster components incorporated in models to simulate anomalous behavior 1 of water, has been predicted to be cyclic and planar 2b and has been structurally characterized within MOFs by a number of groups. 13 A polymeric chain structure having cyclic tetramers as its basic units has recently been discovered in organic crystalline hosts. 14,15 Herein we report a corner-sharing highly ordered tetrameric water chain with additional water forming a dimeric crown (Figure 1). The chains act as sidewalls, supporting 2D metal-carboxylate sheets, to generate a 3D supramolecular host having rectangular channels (Figure 2). This unique host accommodates guest 2-amino-4- picoline ligands in their protonated forms within the channels. 16 The presence of a cyclic dimeric crown of the tetrameric water chain is unprecedented, neither predicted theoretically nor observed experimentally, and has rendered the present water assembly a unique topology. This is also the first report of an infinite 1D tetrameric water chain in a metal-organic environment. The complex 1, {[Cu(mal) 2 ](picH) 2 ‚5H 2 O} n [mal ) C 3 H 2 O 4 ) malonate dianion; picH ) C 6 H 8 N 2 H ) protonated 2-amino-4- picoline], was synthesized from purely aqueous media simply by mixing the reactants in stoichiometric ratio. 16 Elemental (C, H, N) analyses, thermogravimetric analyses (TGA), IR spectra, and X-ray powder diffraction (XRPD) studies characterized 1, and its structure was established by single-crystal structure determination. Ab initio * To whom correspondence should be addressed. E-mail: smukhopadhyay@chemistry.jdvu.ac.in. ² Department of Chemistry, Jadavpur University. § Department of Physics, Jadavpur University. ‡ Departamento de Quı ´mica Inorga ´nica, Universidad de Granada. ⊥ Department of Chemistry, National Changhua University of Education. Figure 1. Corner-shared crowned infinite water chain, displaying the spirocyclic topology of tetramers around the chain axis (shown as arrow). The homodromic donor-acceptor arrangement has been indicated as blue circle. Figure 2. Cu(II)-malonate planes supported by water chains forming rectangular channels with brick-wall topology. Color code: Cu, yellow; O, red; N, blue; C, light-purple; H, tan. CRYSTAL GROWTH & DESIGN 2007 VOL. 7, NO. 2 212 - 214 10.1021/cg060837r CCC: $37.00 © 2007 American Chemical Society Published on Web 01/04/2007