Versatile functionalities in MOFs assembled from the same building units: interplay of structural flexibility, rigidity and regularity

Abstract

A systematic study of the formation of Cu(II) metal–organic frameworks (MOFs) with 1,4-naphthalene dicarboxylate (1,4-ndc) was carried out by varying solvent and temperature that resulted four new MOFs {[Cu(1,4-ndc)·H₂O·3H₂O} (1), {[Cu(1,4-ndc)(MeOH)]·MeOH} (2), {[Cu(1,4-ndc)(H₂O)]·1.8H₂O} (3) and {[Cu₂(μ-OH)₂(1,4-ndc)](H₂O)} (4). Single crystal structural analyses reveal that a paddle-wheel Cu₂(CO₂)₄ core is the secondary building unit in 1–3 and extended to different dimensionality by the 1,4-ndc ligand. Compound 1 shows a unique 2-fold interpenetrated 3D biporous structure with hydrophobic and hydrophilic channels. Compounds 2 and 3 have 2D networks with different orientations of the 1,4-ndc ligand and provide a 1D supramolecular channel structure. Compound 4 was characterized by IR, CHN, PXRD and FESEM analyses. All the frameworks show permanent porosity suggested by the CO₂ sorption studies. Dehydrated frameworks of 1 and 4 exhibit gas storage properties whereas 2 shows highly selective gated MeOH sorption over H₂O. Compound 4 shows ferromagnetic ordering, suggesting coexistence of multiple functionalities within the same framework. Overall, we have fabricated MOFs with adaptable functionalities supported by structural regularities based on the same building units.