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 (H₂tp) and 1,3-bis(4-pyridyl)propane (bpp) have afforded four coordination polymers at room temperature, [Zn(μ-tp)(μ-bpp)]_n·2nH₂O (1), [Cd₂(μ-tp)₂(μ-bpp)₃]_n·2nH₂O (2), [Cd(μ-tp)(μ-bpp)(H₂O)]_n·nH₂O (3), and [Cd₂(μ-tp)(μ-bpp)₂(bpp)₂Br₂]_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 6⁶ 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 6¹⁰ 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.