supplementary materials

Coordination polymers are prepared by employing a wide variety of linking ligands possessing pyridyl–pyridyl, pyridyl–amine, furan–furan, thiophene–thiophene, or pyridyl–carboxylate terminals. For instance, bis(pyridyl)- and dicarboxylate-type linking ligands have long been utilized in preparing such polymers (Robin & Fromm, 2006). In particular, those containing the pyridyl–carboxylate terminals are intriguing due to the presence of both a harder carboxylate oxygen donor and a softer pyridyl nitrogen donor in them. The ligands of this type were employed to prepare unique polymers containing both d- and f-block metals within their frameworks (Hu et al., 2012; Chen et al., 2010; Tang et al., 2010; Yue et al., 2011; Zhu et al., 2010). 6-(Nicotinamido)-2-naphthoic acid (HL) belongs to the pyridyl–carboxylate-type linking ligands, and we recently reported its preparation and structure (Song & Lee, 2012). Our research group also reported the molecular structures of two other related linking ligands (Han & Lee, 2012; Zheng & Lee, 2012). We report herein the structure of a two-dimensional Cu polymer of the HL ligand, which is the first d-block coordination polymer of this ligand.

Fig. 1 shows an asymmetric unit of the title polymer, which consists of one half Cu²⁺ ion, one 6-(nicotinamido)-2-naphthoato ligand (L), one half aqua ligand, and one lattice water molecule. The Cu1 and O4 atoms lie on the crystallographic twofold axis, and the remaining atoms occupy general positions. The Cu²⁺ ion is coordinated to two oxygen atoms from two ligands and two nitrogen atoms from another two ligands to form a distorted square plane. The Cu1···O4 length (2.490 (3) Å), which is represented by a dotted line in Fig. 1, is extremely long, considering the covalent radii of Cu (1.28 Å) and O (0.66 Å) atoms. The van der Waals radii of Cu and O atoms are 1.40 and 1.52 Å, respectively, and therefore the Cu1···O4 bond may be best described as a strong van der Waals contact. Consequently, the coordination sphere of the Cu²⁺ ion may be thought of as square pyramidal, if the Cu1···O4 van der Waals contact is included. The molecular plane, defined by the two O and two N atoms, is extremely distorted from the planarity with the average atomic displacement of 0.328 (1) Å. Two carboxylate oxygen atoms act differently; one (O1) is coordinated to the Cu²⁺ ion and the other (O2) acts as a H-bond acceptor. The terminal carboxylate and pyridyl groups are bonded to the Cu²⁺ ions, indicating that this ligand behaves as a linking ligand. The amide group (–CONH–) does not coordinate to the metal ion, and the carbonyl oxygen (O3) acts as a H-bond acceptor and the N–H bond behaves as a H-bond donor. In fact, all of the hydrogen atoms in the amide group and lattice water molecule participate in the hydrogen bonds of the O–H···O or N–H···O types (Table 1). Fig. 2 shows a projection of the title polymer along the c-axis. The repeat unit consists of four ligands and four Cu²⁺ ions. This unit contains 56 atoms (4 Cu²⁺ ions and 52 ligand atoms) with the Cu²⁺···Cu²⁺ separation of 15.2045 (4) Å. The repeat units are connected by the ligands to form a 2-D layer in the [110] direction.