Microporous Metal−Organic Frameworks Formed in a Stepwise Manner from Luminescent Building Blocks

A series of trivalent lanthanides (Sm, Eu, Gd, Tb, Dy) have been complexed to the dianionic ligand, 4, 4'-disulfo-2, 2'-bipyridine-N, N'-dioxide, L, in a 3: 1 ratio to form trianionic complex building blocks. These units were then cross-linked into a network solid by addition of BaCl2 to form mixed-metal networks of formula Ba2 (H2O) 4LnL3 (H2O) 2 (H2O) nClinfinity, Ln = Sm3+ (1), Eu3+ (2), Gd3+ (3), Tb3+ (4), Dy3+ (5). The networks were isostructural and contained open channels which readily absorbed and desorbed water accompanied by a spongelike shrinkage and expansion of the host. CO2 sorption measurements confirmed microporosity giving a DR surface area of 718 m2/gm and an average pore size of 6. 4 A. Ligand L sensitized all the lanthanide ions with the exception of Gd3+. Studying the series of Ln complexes allowed the determination of the triplet state energy of L which is itself a new ligand for sensitization purposes. The luminescent properties of the lanthanide building blocks were retained in the porous network solid. From the luminescence data, it was possible to attribute the spongelike properties of the network to the Ba2+ coordination sphere rather than the Ln3+ center. Networks were characterized by X-ray crystallography, PXRD, DSC/TGA, water vapor and gas sorption, and luminescence spectroscopy.