Two Cd-MOFs with different types of channels based on phenylimidazole dicarboxylic acids: Synthesis, crystal structure and solid fluorescence properties

The reaction of cadmium(II) nitrate with two phenylimidazole dicarboxylic acids, 2-phenyl-1H-imidazole-4,5-dicarboxylic acid (H3PhIDC) and 2-p-methoxyphenyl-1H-imidazole-4,5-dicarboxylic acid (p-H3MOPhIDC), produce two new cadmium(II) organic frameworks (Cd-MOFs), namely [Cd4(HPhIDC)4(CH3CN)(H2O)]n (1) and {[Cd2(p-HMOPhIDC)2(H2O)2]•DMF}n (2). Structural analyses show that although 1 and 2 are both three-dimensional (3-D) network skeletons formed by the connection of phenylimidazole dicarboxylic acid, their channel types and porosity (8.8% for 1, 25.1% for 2) are different. The channel of 1 is a quadrilateral channel containing six Cd(II) ions, whereas the channel of 2 is a double channel containing ten Cd(II) ions in a staggered arrangement of large and small quadrilaterals. The difference in the structure and size of the channels of Cd-MOFs may be attributed to the bridging mode of the phenylimidazole dicarboxylic acid ligands. In addition, the fluorescence properties of 1 and 2 at room temperature in solid state were also studied.