Syntheses, structures, and luminescent properties of six new zinc(II) coordination polymers constructed by flexible tetracarboxylate and various pyridine ligands

Under solvothermal conditions, six new Zn(II) coordination polymers, [(CH₃)₂NH₂]₂[Zn(L)]·2H ₂O (1), [Zn₂(L)(py)₂] (2), [Zn ₂(L)(bpe)₂]·bpe·6H₂O (3), [Zn₂(L)(bpe)(DMA)(H₂O)]·5H₂O (4), [Zn₂(L)(bpy)_0.5(H₂O)₂]·2. 5H₂O (5), and [Zn₂(L)(bpe)(H₂O)]·3H ₂O (6) [H₄L = 5,5′-(p-xylylenediamino)-1,1′,3, 3′-(benzenetetra-carboxylic acid), py = pyridine, bpy = 4,4′-dipyridine and bpe = 1,2-bis(4-pyridyl)ethane], have been synthesized by employing a flexible tetracarboxylic acid H₄L and different auxiliary pyridine-based ligands. In 1-6, all L^4- ligands are 4-connected nodes; however, the diverse configurations of the two terminal isophthalate units of L^4- around the central -NHCH ₂PhCH₂NH- spacer lead to various topological nets. 1 shows a three-dimensional (3D) 2-fold interpenetrated 4-connected dia network resulting from the vertical configuration of the two isophthalate units of L^4-. 2 displays a 3D (4,4)-connected pts net in which the two isophthalate units of L^4- adopt a parallel configuration. The two isophthalate units of L^4- in 3 are also almost parallel, resulting in an intriguing 3D 2-fold interpenetrated network with the (4,4)-connected bbf net. 4 is a two-dimensional bilayer structure, extending into a 3D supramolecular framework through interlayer hydrogen-bonding interactions. 5 and 6 disclose similar 3D structural architectures, in which the two isophthalate units of L^4- are almost vertical and exhibit tetrahedral topological nodes, inducing a rare (4,5)-connected xww net and an unprecedented (4,6)-connected network, respectively. The thermal stabilities and luminescent properties of 1-6 have also been studied in detail. The complexes exhibit intense solid-state fluorescent emissions at room temperature.