Two unusual binodal highly-connected 3D networks constructed with mutiflexible ligands

Abstract

By employing 5-oxyacetateisophthalic acid (H₃L) and different flexible imidazole ligands, two new distinct three-dimensional (3D) metal-organic frameworks (MOFs), namely, [Co₄(μ₃-OH)₂L₂(bime)]_n·nH₂O (1) and [Co₄(μ₃-OH)₂L₂(bimb)₂]_2n·3.5nH₂O (2) (bime = 1,2–bis(imidazol-1′-yl)-ethane), bimb = 1,4-bis (imidazol-1′-yl)butane), were solvothermally synthesized and structurally characterized by single-crystal X-ray diffraction. Both compounds 1 and 2 exhibit similar structural frameworks resulting from a chair-like [Co₄(OH)₂]⁶⁺ tetranuclear cluster extended by mutiflexible ligands, but the bridging modes of the H₃L ligand and the coordination environments of the metal centers are different. Detailed structural analysis revealed that, compound 1 exhibits a unique 3D binodal (4,10)-connected (3.4⁵)(3⁴.4¹².5⁸.6¹⁴.7⁵.8²) topology, whereas compound 2 presents an unusual 3D binodal (3,10)-connected (4³)₂(4¹⁰.6³³.8²) topology because of the second imidazole ligands. The thermal stabilities and magnetic properties of the two compounds were also studied.