supplementary materials

Inorganic-organic coordination polymers have been a focus of contemporary research interest not only because of the intriguing variety of architectures and topologies but also because of their potential application in gas storage, catalysis, as molecular magnets, in molecular recognition and photoluminescene (Stang & Olenyuk,1997; Moulton & Zaworotko, 2001; Eddaoudi et al., 2001; Bradshaw et al., 2005). Over the past few decades considerable efforts have documented many networks with various structural motifs including honeycomb, brick-wall, rectangular grid, bilayer, ladder, herringbone, diamondoid and octahedral geometries (Gable et al., 1990; Fujita et al., 1994; Yaghi & Li, 1995; Losier & Zaworotko, 1996; Withersby et al., 1999; Li et al., 1999). Building blocks based on aromatic acids, such as benzoic acid and/or its substituted derivatives, have been used in the construction of coordination polymers. However, there are few examples of metal derivatives of 3,5-dinitrosalicylic acid, and examples of crystal structure reports are limited to silver and tin complexes only. 3,5-Dinitrosalicylic acid is, owing to its versatile coordination modes, an important multidentate ligand for metal complexes (He et al., 2006). Recently, some new structures with the 3,5-dinitrosalicylicate have been synthesized by our group (Song & Xi (2006), 2006; Song, Guo & Guo, 2007; Song, Guo & He, 2007; Song,Guo & Zhang, 2007; Song, Yan et al., 2007).

With the intention of studying the influences of aromatic bridging ligands on the frameworks of possible structures, we chose another non-chelating ligand, 3-hydroxyprridine, as a second ligand (Gao et al., 2005), and a new coordination polymer, [Cu(C₇H₃N₂O₇)(C₅H₅NO)]_n, (I), was successfully synthesized.

The coordination environment of the copper center in complex (I) is depicted in Fig. 1. The asymmetric unit contains one Cu^II ion, one 3,5-dinitro-2-oxidobenzoate ligand and a 3-hydroxypyridine ligand. Coordination by one N atom and three O atoms from two different 3,5-dinitro-2-oxidobenzoate ligands and 3-hydroxypyridine ligand create a square planar Cu^II center, which is augmented by a less tightly bonded fifth phenol oxygen atom to form a square pyramidal five-coordinated complex with a basically flat base. The compound exhibits a double chain structure, in which the 3,5-dinitro-2-oxidobenzoate and 3-hydroxypyridine both act as bridging ligands interconnecting adjacent copper(II) centers to form an infinite double stranded chain along the b axis of the unit cell (Fig 2.). These double stranded chains are stabilized by intra-chain π-π interactions, and further linked through O—H···O hydrogen bonding interaction involving the hydroxyl group of the 3-hydroxypyridine ligand as the H-donor and a nitryl group of the 3,5-dinitro-2-oxidobenzoate ligand as the acceptor, thus forming a three-dimensional supramolecular network (Fig. 3). The centroid-to-centroid distance of adjacent aromatic rings is 3.719 (7) Å.