Highly Efficient Bifunctional Amide Functionalized Zn and Cd Metal Organic Frameworks for One-Pot Cascade Deacetalization–Knoevenagel Reactions

A pyridine-based amide functionalized tetracarboxylic acid, 5,5′-(pyridine-2, 6-dicarbonyl)bis(azanediyl)}diisophthalic acid (H(4)L), was synthesized and its coordination chemistry toward zinc(II) and cadmium(II) ions was studied. The reactions of H(4)L with Zn(NO(3))(2).6H(2)O and Cd(NO(3))(2).4H(2)O led to its full or partial deprotonation, respectively, and the formation of the 2D coordination polymers [Zn(2)(L)(H(2)O)(4)](n).4n(H(2)O) (1) and [Cd(3)(HL)(2)(DMF)(4)](n).4n(DMF) (2) (DMF = N,N'-dimethylformamide), respectively. They were characterized by elemental analysis, FT-IR, photoluminescence, thermogravimetry, and single-crystal and powder X-ray diffraction. In 1, the L(4−) ligand is planar with every carboxylate anion binding a Zn(II) cation and giving rise to a 2D grid with the metals with tetrahedral environments. In 2, the combination of bridging HL(3−) and dimethylformamide to form trinuclear Cd(II) clusters engenders secondary building block units and generates a layer-type 2D network with the metals with octahedral and pentagonal bipyramid coordination geometries. The topological analyses of 1 and 2 reveal 2,4-connected and 3,6-connected binodal nets, respectively. On account of the presence of Lewis acid (Zn or Cd centers) as well as basic (uncoordinated pyridine and amide groups) sites, 1 and (to a much lower extent) 2 effectively catalyze the one-pot cascade deacetalization-Knoevenagel condensation reactions under quite mild conditions. They act as heterogeneous catalysts, being easy to recover and recycle without losing activity.