Hydrothermal synthesis and characterization of metal-organic networks with helical units in a mixed ligand system

Hydrothermal reactions between mixed ligands (4,4'-oxybis(benzoate) and 1,3-bis(4-pyridyl) propane) and Co(NO3)(2)center dot 6H(2)O afford two novel helical metal-organic networks Co(C14H8O5)(C13H14N2) 1 and Co(C14H8O5)(C13H14N2)center dot H2O 2. Compound 1 has a 2-D layer network and the main body of the layer is composed of alternate right-handed and left-handed helical chains by sharing cobalt ions. The distance of the repeating parts of the helical chains is ca. 10.0 angstrom and the size of the helical channels is ca. 7.0 x 7.0 angstrom. In contrast, compound 2 has a 2-D interpenetrated double-layer network and each monolayer is composed of homochiral helical chains by sharing cobalt ions. The distance of the repeating parts of the helical chains is ca. 12.1 angstrom and the size of the helical channels is ca. 7.0 x 7.0 angstrom. Interestingly, each helical chain of 2 is constructed by alternate (4,4'-oxybis(benzoate) and 1,3-bis(4-pyridyl) propane) and cobalt ions. Moreover, two independent monolayers constructing a double-layer are assembled in a homochiral fashion and adjacent double-layers exhibit opposite chirality. The magnetism analysis indicated that compounds 1 and 2 show antiferromagnetic exchange interaction.