Metal-Controlled Assembly of Coordination Polymers with the Flexible Ligand 1,1‘-Biphenyl-2,2‘-dicarboxylate Acid

To determine the influence of metal ions on the formation of metal−organic frameworks, five new coordination
polymers, [Pb6(dpa)4O2]n (1), [Ag2(dpa)]n (2), [Nd2(dpa)3(H2O)2]n (3), [Zn(dpa)(H2O)]n (4), and [Cd2(dpa)2(phen)2(H2O)2]n (5), have
been hydrothermally synthesized from 1,1‘-biphenyl-2,2‘-dicarboxylate acid (dpa). Complex 1 is a one-dimensional chain structure
constructed from a new building unit, Pb6O18, which is connected by four different dpa molecules. Complex 3 is also a one-dimensional chain structure but is composed of a different building unit bridged by three dpa molecules. This complex is further
extended into a two-dimensional supramolecular framework. Like complex 3, complex 4 is a two-dimensional supramolecular
framework, which is connected by one-dimensional chains through π−π interactions and hydrogen bonding interactions. Complex
5 is a three-dimensional metal−organic supramolecular coordination polymer that possesses rectangular cavities. Different from the
above four complexes, complex 2 is a two-dimensional covalence structure. To our knowledge, this is the first two-dimensional
coordination polymer composed of metal ions and the dpa ligand. Furthermore, at room temperature, complex 4 exhibits strong
photoluminescence.