Scorpion-shaped carboxylate ligand tailored molecular square, bilayer, self-threading and (3,6)-connected nets

Abstract

A novel designed scorpion-shaped 5-oxyacetateisophthalic acid (H₃OABDC) was used to construct a series of luminescent metal–organic frameworks, namely [Zn₂(HOABDC)₂(phen)₂(H₂O)₂]_n·nH₂O (1), [Zn₂(OABDC)(4,4′-bipy)(μ₂-OH)(H₂O)]_n·4/3nH₂O (2), [Cd₃(OABDC)₂(4,4′-bipy)₄(H₂O)₄]_n·2nH₂O (3), [Cd₂(OABDC)(phen)₂(μ₃-OH)]_n·1/3nH₂O (4), and [Zn₈(OABDC)₄(2,2′-bipy)₄(μ₂-OH)₄]_n·2nH₂O (5) (bipy = bipyridine, phen = 1,10-phenanthroline). Complex 1 features a discrete molecular square and π–π and C–H⋯π interactions between molecular squares give rise to a 2D sheet. Complex 2 shows an unusual 2D bilayer architecture with (3,5)-connected topology. A prominent structural feature in 3 is the self-threading 2D layered structure. Both 4 and 5 exhibit (3,6)-connected topology. In 4, an extraordinary folded four-step-ladder Cd₄(OH)₂ unit acts as 6-connected node and the framework is 2D (3,6)-connected net. While in 5, the Zn₂(OH) unit adopts octahedral geometry and the whole framework features a 3D (3,6)-connected rutile (rtl) topology. Photoluminescence studies revealed that these complexes are interesting blue, green and orange luminescent materials. The thermal stabilities of these complexes are also discussed.