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

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.