Acyclic water pentamer induces novel supramolecular ribbed sheet: Cooperativity and competitiveness of weak and covalent forces? Atish Dipankar Jana 1 , Rajat Saha, Golam Mostafa * Department of Physics, Jadavpur University, Jadavpur, Kolkata 700 032, India article info Article history: Received 7 October 2009 Received in revised form 4 December 2009 Accepted 8 December 2009 Available online 14 December 2009 Keywords: Water pentamer Self-assembly Cooperativity Malonate 1,3-Bis(4-pyridyl)propane abstract The 1D chain complex [{Cu(II)(bpp)(malonate)(H 2 O)}(H 2 O) 4 ] n (1) (bpp = 1,3-bis(4-pyridyl)propane) self- assembles to form a 2D ribbed sheet stabilized by an acyclic pentameric water cluster, which in turn, influences the conformation of the bpp ligand. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction To date a large number of water clusters isolated in a number of crystal hosts including oligomers (tetramer [1,2], pentamer [3], hexamer [4], heptamer [5–7], octamer [8,9], decamer [10], dodeca- mers [11] etc.) and polymers (1D chain [12], helix [13,14], tape [15] and 2D sheet [16]) have been structurally characterized and pro- vided detailed information about cooperative hydrogen bonding behavior in these diverse geometries. Coordinated water molecules in metal complexes also take part in the cluster formation and even with the participation of coordinated water molecules the cluster attains its regular geometry in many cases [17]. Recently, the advantage of water cluster research, the upsurge in studying small water clusters in different environments by systematically varying the size and the research to understand the properties of the con- densed phase have been well-documented in a special issue of Syn- thesis and Reactivity in Inorganic, Metal–Organic, and Nano-Metal Chemistry [18]. Curiously, it has been seen that water oligomers of even number of water molecules are abundant in metal–organic frameworks whereas odd numbered clusters are scarcely observed [19]. In the current article we present an acyclic water pentamer in the context of self-assembly of a coordination polymer. Till date, only two acyclic water pentamers have been reported in literature [20,21]. The overall self-assembly of a crystalline material is the penultimate outcome of the competitiveness as well as cooperativ- ity of weaker forces (hydrogen bonding, p–p and C–H...p interac- tion etc.) and stronger forces (coordinative and covalent) in the organization of metal nodes with flexible organic ligands. The pres- ent crystal structure nicely represents an example, where this competitiveness and cooperativity has been borne out in the self- assembled supramolecular structure. In this paper we wish to highlight the cooperativity among a set of water molecules, malon- ate ligands and flexible 1,3-bis(4-pyridyl)propane(bpp) ligands, resulting the organization of water molecules in the form of an acyclic water pentamer. 2. Experimental 2.1. Materials and general methods All the reagents and solvents for synthesis were commercially available and used as received without further purification. Ele- mental analyses (C, H, N) were performed on a Perkin-Elmer 240C analyzer. IR spectra were measured from KBr pellets on a Nicolet 520 FTIR spectrometer. 2.2. Synthesis of complex 1 Copper-malonate was prepared by adding CuCO 3 ÁCu(OH) 2 slowly to the aqueous solution of malonic acid with continuous 0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2009.12.009 * Corresponding author. E-mail address: mostafa@phys.jdvu.ac.in (G. Mostafa). 1 Present address: Department of Physics, Sripat Singh College, Jiaganj, Murshida- bad 742 123, India. Journal of Molecular Structure 966 (2010) 64–68 Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc