Topological Diversity of Coordination Polymers Containing the Rigid Terephthalate and a Flexible N,N′-Type Ligand: Interpenetration, Polyrotaxane, and Polythreading

Reactions of zinc(II) or cadmium(II) salts with terephthalic acid (H 2 tp) and 1,3-bis(4-pyridyl)propane (bpp) have afforded four coordination polymers at room temperature, [Zn(μ-tp)(μ-bpp)] n ·2 n H 2 O ( 1 ), [Cd 2 (μ-tp) 2 (μ-bpp) 3 ] n ·2 n H 2 O ( 2 ), [Cd(μ-tp)(μ-bpp)(H 2 O)] n · n H 2 O ( 3 ), and [Cd 2 (μ-tp)(μ-bpp) 2 (bpp) 2 Br 2 ] n ( 4 ). Single-crystal X-ray diffraction has revealed interesting topological features for these compounds. In 1, the Zn atoms act as 4-connected nodes bridged by the tp and bpp ligands to give a 3-fold interpenetrated 3D network with a unique 6 6 topology, which is evidently distinct from 4-connected diamondoid networks. 2 represents the first example of a 2-fold interpenetrated coordination polymer, which possesses a 5-connected 3D framework with a unique 6 10 topology constructed from Cd nodes and tp and bpp spacers. 3 manifests a polyrotaxane motif comprised of two interlocked sets of identical sheets, which result in a 2D → 2D polythreaded layer. Parallel mutual polythreading of 2D layers with dangling bpp ligands is observed in 4, involving five polymeric layers at a time and thus affording a 3D architecture. All compounds were characterized by infrared spectroscopy, elemental analysis, thermogravimetric analysis, and their fluorescence properties were also investigated.