research papers 102 http://dx.doi.org/10.1107/S2052520615020983 Acta Cryst. (2016). B72, 102–108 Received 30 June 2015 Accepted 5 November 2015 Edited by J. Lipkowski, Polish Academy of Sciences, Poland Keywords: coordination polymer; hydrogen bonding; metal–organic host; water trimer; Glaser coupling. CCDC reference: 998943 Supporting information: this article has supporting information at journals.iucr.org/b A double stranded metal–organic assembly accom- modating a pair of water trimers in the host cavity and catalysing Glaser coupling Subhashis Pradhan, a Dohyun Moon b * and Rohith P. John a * a Department of Applied Chemistry, Indian School of Mines, Dhanbad, Jharkhand 826004, India, and b Beamline Division, Pohang Accelerator Laboratory, Pohang, Kyungbuk 790784, Republic of Korea. *Correspondence e-mail: dmoon@postech.ac.kr, rohithjohn@gmail.com A supramolecular compound, catena-poly{[Cu 2 (1,3- 2 -(1a)) 2 ( 2 - ter) 2 (H 2 O) 2 ] n (6H 2 O) n } (1) has been synthesized using (1a) [(1a = N 1 ,N 3 ,N 5 - trimethyl-N 1 ,N 3 ,N 5 -tris((pyridin-4-yl)methyl)-1,3,5-benzene tricarboxamide] and terephthalate (ter) as the pillaring unit by self-assembly. The terephthalate units are connected by copper(II) ions forming a single strand, while a pair of such strands are then linked by (1a) via two pyridyl terminal arms bound to copper(II) nodes on either side forming a one-dimensional double stranded assembly propagating along the c axis. The compound crystallizes in the Fdd2 space group. The cavity created in the interior of this double strand assembly trap six water molecules and are stabilized by hydrogen bonding with the host. The arrangement of the pair of acyclic water trimers in isolated cavities of (1) is such that it resembles a closed-bracket-like formation. The Hirshfeld surface analysis of (1) reveals the presence of strong intermolecular hydrogen-bonding interactions between one-dimensional ladder-like units and with the water trimer in the host cavity. The copper(II)-containing coordination polymer also acts as an efficient catalyst for the Glaser–Hay homo-coupling reaction. 1. Introduction The quest for identifying water clusters in various environ- ments has gained significant attention in the last two decades because of their importance in understanding ice formation, solution chemistry and various other biochemical processes. The arrangement of structured water plays a significant role in determining the folding pattern of proteins and hence the activity of enzymes. Among water clusters, trimers, tetramers, pentamers, hexamers and higher members were predicted (Shields et al. , 2010; Keutsch et al., 2003; Pe ´rez et al., 2012; Miliordos et al. , 2013). Efforts to observe such water clusters experimentally have yielded interesting results with various types of clusters being observed in organic (Custelcean et al., 2000; Atwood et al., 2001; Wang et al., 2012) and inorganic (Xu et al., 2012; Li et al., 2009) templates, and in metal–organic assemblies (Luo et al. , 2011, and references therein), in addi- tion to liquid helium environments at very low temperatures (Nauta & Miller, 2000). The cooperative interaction between a water cluster and its surroundings is exemplified by the observation of a water decamer with an ice-like molecular arrangement (Barbour et al., 1998) in the space created by the packing of dinuclear cage units composed of dipodal amide- based ligands and Pd 2+ . A large number of cyclic or acyclic water clusters are reported in crystal hydrates and in metal– organic assemblies (Ghosh & Bharadwaj, 2003, 2005; Luo et ISSN 2052-5206 # 2016 International Union of Crystallography