supplementary materials

Hydroxypyridines (PyOH), such as 2-, 3- and 4-PyOH, have attracted great attention in the field of crystal engineering as good candidates for the construction of supramolecular systems because they are bifunctional ligands that are not only capable of coordinating to metal ions but can also form classical hydrogen bonds as both donors and acceptors (Holis & Lippard, 1983; Klausmeyer & Beckles, 2007). 4-PyOH has two tautomers, dominated by the presence of keto form in polar solvents (Deng et al., 2005; John & Urland, 2006). Thus, the protonated N atom can act as hydrogen bond donor and the PyOH uses O atom to coordinate to metal. However, the coordination chemistry of 4-PyOH ligand is still underveloped and only a few complexes have been structurally characterized in recent years (Gao et al., 2004; Leng & Ng, 2007; Li, Yan et al., 2005). In order to gain further insight into the metal-binding modes of the 4-PyOH ligand, we introduced Ag^I ion into the coordination system of the 4-PyOH ligand. In the present paper, the Ag^I ion only coordinates via the unfavoured O atom of 4-pyridone ligand, producing the title one-dimensional coordination polymer, which exhibits a three-dimensional hydrogen-bonded architecture.

The coordination environment of Ag^I centre is shown in Fig. 1. Each Ag^I atom is coordinated by two O atoms from two different 4-pyridone ligands and two O atoms from one nitrate anion (Table 1), displaying a nearly planar coordination geometry. Two 1H-pyridin-4-one ligands use their O atoms to bridge two symmetrically related AgNO₃ units to form a dimer, with an Ag···Ag separation of 3.680 (2)Å. The adjacent dimers are linked through weak Ag···Ag interactions [3.1511 (4)Å] into a one-dimensional polymeric chain, which is also stabilized by weak Ag···O interactions [2.765 (2)Å] and intrachain π–π interactions (Fig. 2). The centroid–centroid and interplanar distances between adjacent pyridyl rings are 3.623 (4) and 3.301 (4)Å, respectively, thus indicating a weak π–π contact (Deisenhofer & Michel, 1998; Li, Yin et al., 2005; Pan & Xu, 2004; Wu et al., 2003). The polymeric chain shows a staircase-like array, with an Ag···Ag···Ag angle of 63.51 (4)° between three successive Ag atoms along the chain. Such an array in the chain may be explained to avoid steric hindrance. N—H···O hydrogen bonds between the ligand N atoms and the nitrate O atoms (Table 2) link adjacent chains to furnish a lamellar layer. The interlayer N—H···O and C—H···O hydrogen bonds (Table 2) further assemble the neighbouring layers, giving rise to a three-dimensional supramolecular network (Fig. 3).