Two-dimensional metal–organic frameworks with blue luminescence

Three new isostructural two-dimensional metal–organic frameworks (MOFs), [M(bpydc)(H2O)·H2O]n where M = Zn (1); Co (2); Ni (3) and the bpydc is 2,2′-bipyridine-5,5′-dicarboxylate), were prepared by various methods such as hydrothermal, ultrasonic and microwave-assisted synthetic methods. Microcrystalline 1 could be obtained by using ultrasonification or microwave irradiation in a short time. Their solid-state structures were revealed by X-ray crystallography. The coordination environment of the metal ions is distorted octahedral geometry. The metal ions are coordinated by two nitrogen atoms from the bipyridyl moiety, two oxygen atoms from one carboxylate in a bidentate manner, one oxygen atom from another carboxylate in a monodentate manner, and one oxygen atom from the aqua ligand. The multiple coordination modes of the bpydc ligand led to a novel topologically interesting two-dimensional sheet structure; a 6-connected uninodal net with Schläfli symbol of 33·44·55·62·7. Thermal and luminescence properties of the three MOFs were also investigated. The weight maintained constant in the range 290–342 °C for 1, 250–470 °C for 2, and 275–470 °C for 3 after the initial weight loss related to the dehydration steps. In particular, [Zn(bpydc)(H2O)·H2O]n (1) displays strong solid state blue luminescence.