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

Abstract

The reaction of copper(II) or zinc(II) nitrate with pyridine-2,3,5,6-tetracarboxylic acid (H₄pdtc) in the presence of 4,4′-bipyridine (4,4′-bpy) afforded two 3D porous framework compounds, [Cu₃(H₂O)₄(Hpdtc)₂(4,4′-bpy)₂]·3H₂O (poly[[tetraaqua(bi-μ₃-pyridine-2,3,6-tricarboxylato-5-tetracarboxylic acid)(bi-μ₂-4,4′-bipyridine)tricopper(II)]trihydrate]; 1) and [Zn₄(H₂O)₆(pdtc)₂(4,4′-bpy)]·5H₂O (poly[[hexaaqua(bi-μ₅-pyridine-2,3,5,6-tetracarboxylato)(mono-μ₂-4,4′-bipyridine)tetrazinc(II)]pentahydrate]; 2). Each Hpdtc³⁻ 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 pdtc⁴⁻ is slightly changed in 2, the pdtc⁴⁻ 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.