A Two-Dimensional Zinc Coordination Polymer Based on a Pyridyl-Carboxylate Linking Ligand Containing an Intervening Amide Group: [ZnCl(L)]∞(HL = 6-(nicotinamido)-2-naphthoic acid)

Coordination polymers (CPs) and metal–organic frameworks (MOFs) continually gain much attention due to their interesting structures and remarkable applications to a wide range of fields. According to the very recent IUPAC recommendations for the terminology, CPs are coordination compounds with repeating coordination entities extending in 1, 2, or 3 dimensions, and MOFs are coordination networks with organic ligands containing potential voids. IUPAC also recommended the use of the term “coordination networks” to indicate (i) coordination compounds extending, through repeating coordination entities, in 1 dimension, but with cross-links between two or more individual chains, loops, or spiro-links, or (ii) coordination compounds extending through repeating coordination entities in 2 or 3 dimensions. For the successful preparation of such polymeric species, the choice or design of proper linking ligands is essential, and those possessing either pyridyl or carboxylate terminals are typically employed. Several d–f coordination polymers, which contain both dand f-block metals as nodes in their frameworks, were recently constructed from asymmetric linking ligands possessing pyridyl–carboxylate or pyridyl–imidazole terminals. We recently launched a research program that involves the synthesis of novel pyridyl–carboxylate-type linking ligands and their CPs possessing d, f, or d–f metals, and a few linking ligands and their CPs have been prepared. In particular, we became interested in the pyridyl–carboxylate-type ligands containing an amide (–C(O)–NH–) fragment, which might be utilized further for the so-called postsynthetic modification of CPs and MOFs. In this context, our group recently prepared two ligands of this type (HL and HL' in Chart 1), both of which contain a 3-pyridyl and a carboxylate terminals. The ligand HL was employed to prepare a 2D copper coordination polymer with a layer framework, {[CuL2(H2O)]·2H2O}∞. In addition, the ligand HL' was utilized to construct cadmium and nickel coordination polymers: {[Cd(L')2](H2O)}∞ (a 2D layer) and {[Ni(L')2(H2O)2](H2O)}∞ (a 1D double-chain). In order to further examine the linking capability of the ligand HL, we attempted to construct new coordination polymers with it. We herein report the preparation, structure, and thermal behavior of a 2D zinc coordination polymer, [ZnCl(L)]∞. Experimental