A Series of Lead(II)-Organic Frameworks Based on Pyridyl Carboxylate Acid N-Oxide Derivatives: Syntheses, Structures, and Luminescent Properties

Six new lead coordination polymers, namely, [Pb(INO) 2 ]·3H 2 O ( 1 ), [Pb(INO) 2 ·NO 3 ·H 2 O] ( 2 ), [Pb(INO)·Cl] ( 3 ), Na 1.5 [Pb 2 (INO) 5 ]·0.5NO 3 ( 4 ), [Pb 3 (NNO) 4 ·(NO 3 ) 2 ·H 2 O] ( 5 ), and [Pb(NNO) 2 ] ( 6 ), have been prepared by the reaction of Pb(NO 3 ) 2 with isonicotinic acid N-oxide (HINO), or nicotinic acid N-oxide (HNNO), and characterized by elemental analysis, IR, and single-crystal X-ray diffraction. Compound 1, consisting of a one-dimensional (1D) infinite chain, is a three-dimensional (3D) supramolecular framework with a 1D rectanglar channel in which free water molecules locate. The structure of 2 consists of 1D chains built by two parallel INO ligands bridging a pair of rhombic-planar [Pb 2 O 2 ] units, which is further extended into a 2D supramolecular layer via hypervalent interactions and interlayer π-π interactions. Compound 3 consists of a two-dimensional (2D) inorganic layer containing 16-membered rings, which are further linked through μ-INO to generate a unique 3D open framework. In compound 4, the self-assembly based on 2D motifs with side arms leads to the formation of a new type of polythreaded network, which contains 1D channels with guests molecules along the b -axis. In compound 5, NNO ligands in three kinds of coordination modes link to three unique lead centers to generate two kinds of Pb−O chains which are bridged by NNO to give a 2D network. Compound 6 is a 2D layer structure and in the intralayer regions parallel left- and right-handed helical chains exist. In addition, compounds 1, 2, 3, and 6 exhibit strong phosphorescent emissions in the solid state at room temperature. The results of theoretical calculations show that the absorptions of these complexes derive mainly from ligand to ligand charge transfer (LLCT) transitions.