The roles of the coordination modes of bridging ligands for the formation of two 3D metal-organic coordination networks

The reaction of copper(II) or zinc(II) nitrate with pyridine-2,3,5,6-tetracarboxylic acid (H(4)pdtc) in the presence of 4,4'-bipyridine (4,4'-bpy) afforded two 3D porous framework compounds, [Cu-3(H2O)(4)(Hpdtc)(2)(4,4'-bpy)(2)]center dot 3H(2)O (poly[[tetraaqua(bi-mu(3)-pyridine-2,3,6-tricarboxylato-5-tetracarboxylic acid)(bi-mu(2)-4,4'-bipyridine)-tricopper(II)]trihydrate]; 1) and [Zn-4(H2O)(6)(pdtc)(2)(4,4'-bpy)]center dot 5H(2)O (poly[[hexaaqua(bi-mu(5)-pyridine-2,3,5,6-tetracarboxylato)(mono-mu(2)-4,4'-bipyridine)tetrazinc(II)]pentahydrate]; 2). Each Hpdtc(3-)ligand in 1 chelates and bridges two copper(II) cations into a linear network, which is further linked into a 3D porous network by 4,4'-bpy running along three different orientations. When the coordination mode of pdtc(4-) is slightly changed in 2, the pdtc(4-) ligands link the zinc cations into a 3D porous network structure without the assistance of the 4,4'-bpy ligand. The role of the lattice water molecules in 2 was changed from guest molecules to supramolecular linkers in order to join the zinc polyhedra into a 3D supramolecular network structure.