Zn^II coordination polymers constructed with malonate and bipyridyl ligands: Photoluminescence and heterogeneous catalytic reactivity

Four three-dimensional Zn^II frameworks containing malonates and various bipyridyl pillars (4,4′-bipyridine (1), 1,2-bis(4-pyridyl)ethane (2), 1,2-bis(4-pyridyl)ethylene (3) and 1,3-bis(4-pyridyl)propane (4)) have been prepared, and their structures were determined by X-ray crystallography. In all four frameworks, malonate ligands bridge three Zn ions to form two-dimensional layers, and these layers are connected by bipyridyl pillars to form three-dimensional frameworks with the general formula [{Zn(H₂O)(μ- malonate)}₂(μ-bipyridyl)] and which also contain water or acetonitrile solvates. Reactivity studies of compounds 1-4 showed that they catalyzed a heterogeneous transesterification reaction of phenyl acetate and could be reused without any significant loss of activity through five runs. Emissions were observed at 347-365 nm (λ_ex = 313 nm) for 2 and 363 nm (λ_ex = 328 nm) for 3, while compounds 1 and 4 showed no luminescence properties. The thermal stabilities of these complexes were also examined.