Co/Zn metal–organic frameworks with an anthracene-based ligand: cell imaging and catalytic studies†

Abstract

Co-MOF and Zn-MOF were synthesised by reacting CoCl₂·6H₂O/Zn (NO₃)₂·6H₂O with APO [1,1′-(anthracene-9,10-diylbis(methylene)bis(pyridin-1-ium-4-olate))] and benzene 1,3,5-tricarboxylic acid (BTC) in a 2 : 1 : 2 molar ratio employing a solvothermal approach. Both synthesised MOFs were characterized by various analytical techniques viz., elemental analysis, FT-IR, TGA, PXRD, BET and FE-SEM analysis. Single-crystal X-ray diffraction analysis revealed that Co-MOF has three Co(II) centres with two octahedral and one distorted square pyramidal geometry, whereas Zn-MOF has three Zn(II) centres with two Zn(II) distorted tetrahedral and one trigonal pyramidal geometry. Particle sizes, determined via the Debye–Scherrer formula, were approximately 17 nm for Co-MOF and 38 nm for Zn-MOF. The live cell imaging studies of these MOFs on the HepG2 human liver cancer cell line demonstrated non-cytotoxicity and cellular internalization. The MOFs were also tested as catalysts in the multicomponent Biginelli synthesis of biologically relevant 3,4-dihydropyrimidin-2(1H)-ones (DHPMs) (1a–1h). Co-MOF exhibited superior catalytic activity due to the enhanced Lewis acidity of Co(II) relative to Zn(II). Recyclability tests indicated minimal activity loss after four cycles. The proposed mechanism suggested that the Knoevenagel pathway plays an important role in the reaction with the iminium mechanism playing a minor role. The mass spectrometric detection of intermediates excluded the involvement of the enamine pathway. The present study establishes the dual functionality of these nanoscale MOFs in biomedical imaging and sustainable catalysis.