A Molecular Basketwork: Self-Assembly of Coordination Polymers from Zn(II) and Biphenyl-3,4′-dicarboxylate Regulated by Different Flexible Bridging and Chelating N-Donor Ancillary Ligands

Four low-dimensional coordination polymers, [Zn2(bpdc)2(dib)2]n·nH2O (1), [Zn(bpdc)(phen)]n·2nH2O (2), [Zn(bpdc)(bpy)]n·2nH2O (3), and [Zn(bpdc)(H2O)]n (4), (H2bpdc = biphenyl-3,4′-dicarboxylic acid, dib = 1,4-di(1H-imidazol-2-yl)butane, phen = 1,10-phenanthroline, bpy = 2,2′-bipyridine), have been successfully prepared under hydrothermal conditions and characterized by IR, single crystal X-ray diffraction, thermogravimetric analysis (TGA), and luminescence analyses. Self-assembly behaviors of these polymers were entirely directed by N-donor ancillary coligands (bridging or chelating). Complex 1 displays an interesting novel two-dimensional (2D) basketwork, in which Zn(II) ions are knitted by both organic molecules, biphenyl-3,4′-dicarboxylic acid and 1,4-di(1H-imidazol-2-yl)butane, to form an infinite network. Polymers 2 and 3 are infinite zigzag helical chains, and both terminated ligands in 2 and 3 prevent self-assembly to higher dimensional polymers. In 4, a water molecule occupies one of four coordinated positions of Zn(II), and it shows an infinite alternating subloop chains consisting of 8- and 24-membered rings. New coordination modes of the rarely used 3,4-bpdc ligand are reported in 1−4. The results reveal that different secondary building units could tune the process of self-assembly to form low-dimensional structures, and the observed structural motifs can be well regulated by the different chelating or bridging N-donor ancillary ligands. Moreover, complexes 1−4 exhibit strong solid-state luminescence emissions at room temperature.