Heterogeneous catalysis with a coordination modulation synthesized MOF: morphology-dependent catalytic activity

Abstract

We report control over morphology of a micro-porous three-fold interpenetration amide-functionalized Zn(II)-based MOF, [Zn₂(oba)₂(bpta)]·(DMF)₃, TMU-22, (H₂oba = 4,4′-oxybis(benzoic acid); bpta = N,N′-bis(4-pyridyl)-terephthalamide) for Knoevenagel condensation through coordination modulation growth. Micro-rods and -plates of TMU-22 have been prepared via a coordination modulation method using acetic acid and pyridine as modulators, respectively. Several experimental parameters including the effects of the concentration of the modulator, solvent and temperature of the reaction on the size and morphology of the micro-crystals have been investigated. The catalytic performance of TMU-22 micro-sized MOF in the Knoevenagel condensation reaction was evaluated. Moreover, the catalytic activity of TMU-22 was compared to two isoreticular amide-functionalized MOFs, [Zn₂(oba)₂(bpfb)]·(DMF)₅ (TMU-23), and [Zn₂(oba)₂(bpfn)]·(DMF)₂ (TMU-24) (bpfb = N,N′-bis-(4-pyridylformamide)-1,4-benzenediamine; bpfn = N,N′-bis-(4-pyridylformamide)-1,5-naphthalenediamine). It was found that not only the incorporation of amide groups but also the morphologies of the MOF are crucial to obtain an enhanced catalytic performance.