Design and synthesis of microporous metal coordination polymers using polybenzoate ligands

This thesis describes the design, synthesis, crystal structure and properties of about 50 metal coordination polymers based on poly-benzoate ligands. Chapter 2 explores the potential of trimesic acid (TMA-H₃) as a network forming ligand. At room temperature with divalent metal ions this forms two families of salts [M(H₂O)_x(TMA-H )]_n and [M₃(H₂O)_y( TMA)₂]_n depending on pH. Their framework dimensionality is both metal and pH dependent. Larger metals with higher coordination number tended to give higher dimensionality, as did lower pH, which correlated to the degree of ancillary ligation at the metal, i.e., x<< y. The effect of such ligation is best illustrated by the series [Er(H₂O) ₅(TMA)]_n, Er(H₂O)₃( TMA)]_n and [Er(TMA)]_n which have 1-D, 2-D and 3-D networks respectively. The latter polymer is made using the hydrothermal method as is described in Chapter 3. This offers a good way to enhance polymer dimensionality. Both kinetic and thermodynamic control of hydrothermal crystallization is possible. Use of longer time and higher temperature in the hydrothermal crystallization results in relatively stable condensed 3-D network polymers, such as [Cu₃(OH)₃(TMA)] _n.; Chapter 4 deals with some approaches to engineering of pore size and polymer architecture of open framework polymers. The use of larger ancillary ligands such as pyridine, instead of water; results in [M₃( TMA)₂(py)₉]_n M = Cu and Cd, which have large cavities. The extended ligand benzene-hexa-p-benzoic acid [C ₆(C₆H₄COOH)₆] (BHB-H ₆) was synthesized and with Pb2+ forms a 3-D porous solid with 13Å x 8Å 1D channels. The use of pyridine-3,5-dicarboxylic acid (PDA-H₂) allowed formation of [NiLn(OH)( PDA)₂] a material with ferromagnetic character. A chiral polymer [RuCd₂(BDA)₃(H₂O) ₄]_n was formed using two metals and the bipyridinedicarboxylic acid and contains only Δ-[Ru(BDA)₃] units.; Finally solvothermal synthesis with 50% ethanol, or crystallization from dmf; resulted in formation of [Cu₃(TMA)₂(H ₂O)₃]_n. This polymer (Chapter 5) is a stable cubic 3-D microporous solid with intersecting 10Å channels. Sorption studies using N₂ gas show it has a high BET surface area of 692.2 m 2g–1, and a calculated porosity of 41%. The framework is stable to 225°C. The channels hold up to a further ten mole equivalents of water. Dehydration allows chemically functionalization by introducing new ligands such as pyridine to the axial ligand sites.; In summary stable porous metal coordination polymers appear to have the potential to become an important class of microporous materials, which are complementary to zeolites and other established molecular sieves.