Novel metallosupramolecular networks constructed from CuII, NiII, and CdII with mixed ligands:: Crystal structures, fluorescence, and magnetism

Reactions of mixed ligands succinic acid (H(2)suc) and bent dipyridines, such as 2,5-bis(3-pyridyl)-1,3,4-oxadiazole (3-bpo) and its 4-N-donor analog (4-bpo), with inorganic Cull, Ni", and Cd'' salts yield three new metal-organic coordination frameworks {[Cu(suc)(3-bpo)(H2O)(2)]center dot(H2O)(1.75)}(n) (1), {[Ni(suc)(4-bpo)(H2O)(2)]center dot(H2O)(5)}(n) (3), and {[Cd-2(suc)(2)(3-bpo)(2)(H2O)(2)]center dot(H2O)(6.75)}(n) (4), in which the metal centers are linked by bridging ligands 3-bpo/4-bpo and suc(2-) along two directions to form 2D infinite networks. The corrugated 2D nets of 1 and 4, obtained under hydrothermal conditions, align in an interdigitated manner with the presence of significant aromatic-stacking interactions to result in similar 3D architectures. The 2D sheets in 3 are extended by interlayer hydrogen bonds to afford a 3D structure. However, when succinic acid is replaced by fumaric acid (H(2)fum) in the reaction with 3-bpo and Cu" salt, a metallacyclophane [Cu(Hfum)(2)(3-bpo)(H2O)](2)center dot(3-bpo)(2)center dot(H2O)(6) (2) is generated. The binuclear coordinated motifs are hydrogen-bonded to the lattice water chains to furnish a unique 3D channel-like framework, in which the guest 3-bpo molecules are accommodated. The thermal stabilities of these new materials were investigated by thermogravimetric analysis (TGA) of mass loss. The magnetic coupling in complexes 1-3 is antiferromagnetic and very small, which is as expected considering the long organic bridges between the paramagnetic centers. The solid-state luminescence properties of 4 reveal an intense fluorescence emission at 378 nm. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)