A comparison of the coordination preference of Cd, Zn, Cu(II) with flexible homophthalic acid and rigid bipyridine ligands

The mild hydrothermal reaction of Cd, Zn, or Cu(II) acetate salts with the deprotonated flexible linker homophthalic acid (H2hmph) and the rigid molecule 4,4′-bipyridine (bpy) produced the following complexes, featured structurally by the assembly of various metal carboxylate subunits cohered further by the bpy ancillary ligand: {[Cd2(hmph)2(bpy)(H2O)2]·H2O}n (1) manifests cadmium carboxylate zigzag chain motifs, containing the alternation of a hmph-bridged Cd2(hmph)2 dimer and an edge-shared Cd2N4O10 dimer, connected further by the bpy ligands to form a layered structure with a large 50-membered ring; [Zn(hmph)(bpy)]n (2) processes hmph-bridged Cd2(hmph)2 dimer motifs inter-linked further by the bpy ligands to generate mutually embedded layered structures with square (4,4) grids; and {[Cu(hmph)(bpy)]·H2O}n (3) consists of copper carboxylate helix motifs, featuring hmph-bridged CuN2O4 octahedra cross-linked further by the bpy ligands into a twofold-interpenetrating 3D chiral framework with a homochiral topology of a quartz dual net. This well-defined synthetic system was proposed to highlight the fact that organic linkers display markedly different coordination preferences at specific metal ions. In addition, the fluorescence properties of complexes 1 and 2 were rationalized in terms of the local ligand environments in the crystal structures, and magnetic properties of complex 3 are also given.

The Cd, Zn or Cu(II) centers cooperatively coordinated by the deprotonated flexible homophthalic acid and rigid 4,4′-bipyridine molecules produced three new coordination polymers under mild hydrothermal conditions, the structures and properties of which are highly sensitive to the nature of the metal ions.Figure optionsDownload as PowerPoint slideHighlights
► A well-defined synthetic system produces three metal (II) complexes.
► The flexible poly-carboxylate expands the syntheses of coordination polymers.
► The linkers display different coordination preference at the specific metal ion.
► The structures and properties are strikingly sensitive to the metal center.