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)2·6H2O afford two novel helical metal–organic networks Co(C14H8O5)(C13H14N2) 1 and Co(C14H8O5)(C13H14N2)·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 A and the size of the helical channels is ca. 7.0 × 7.0 A. 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 A and the size of the helical channels is ca. 7.0 × 7.0 A. 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.