AUTHOR=Karmakar Anirban , Paul Anup , Rúbio Guilherme M. D. M. , Soliman Mohamed M. A. , Guedes da Silva M. Fátima C. , Pombeiro Armando J. L. 

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

JOURNAL=Frontiers in Chemistry

VOLUME=7

YEAR=2019

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2019.00699

DOI=10.3389/fchem.2019.00699

ISSN=2296-2646

ABSTRACT=<p>A pyridine-based amide functionalized tetracarboxylic acid, 5,5′-(pyridine-2, 6-dicarbonyl)bis(azanediyl)}diisophthalic acid (H<sub>4</sub>L), was synthesized and its coordination chemistry toward zinc(II) and cadmium(II) ions was studied. The reactions of H<sub>4</sub>L with Zn(NO<sub>3</sub>)<sub>2</sub>.6H<sub>2</sub>O and Cd(NO<sub>3</sub>)<sub>2</sub>.4H<sub>2</sub>O led to its full or partial deprotonation, respectively, and the formation of the 2D coordination polymers [Zn<sub>2</sub>(L)(H<sub>2</sub>O)<sub>4</sub>]<sub>n</sub>.4n(H<sub>2</sub>O) (<bold>1</bold>) and [Cd<sub>3</sub>(HL)<sub>2</sub>(DMF)<sub>4</sub>]<sub>n</sub>.4n(DMF) (<bold>2</bold>) (DMF = N,N'-dimethylformamide), respectively. They were characterized by elemental analysis, FT-IR, photoluminescence, thermogravimetry, and single-crystal and powder X-ray diffraction. In <bold>1</bold>, the L<sup>4−</sup> 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 <bold>2</bold>, the combination of bridging HL<sup>3−</sup> 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 <bold>1</bold> and <bold>2</bold> 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, <bold>1</bold> and (to a much lower extent) <bold>2</bold> 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.</p>