Role of Anions in the Formation of Multidimensional Coordination Polymers: Selective Separation of Anionic Toxic Dyes by 3D-Cationic Framework and Luminescent Properties

The role of anions in the formation of diversified coordination polymers (CPs) of a flexible bidentate ligand (L), containing an aliphatic-aromatic spacer (p-xylyl) between amidopyridine moieties, has been explored. The reaction of L with Cd­(II) or Cu­(II) salts of NO3 –, ClO4 –, SO4 2–, and SiF6 2– resulted in the single crystals of eight CPs. The X-ray diffraction analyses of the single crystals reveal that the CPs contain 1D-zigzag (SiF6 2–), open (4,4)-network (NO3 – and SCN–), and the interpenetrated 2D-networks with (4,4)- and (6,3)-topologies and pseudodiamondoid network (SO4 2– and ClO4 –). These results clearly indicate that the presence of tetrahedral anions favored the interpenetration of the 2D- and 3D-networks. The resultant cationic CPs are explored for their dye adsorption ability based on the charge transfer interaction between the framework and ionic dye. Among all CPs, complex 8 containing a 3D-interpenetrated diamondoid network was found to show remarkable ability for the uptake of anionic dyes such as fluorescein dianion (FSD) and methyl orange (MO). The ability of 8 to selectively adsorb anionic dye was utilized for the separation of the MO from cationic dye such as methylene blue. Further, the FSD adsorbed material of 8 was shown to exhibit enhanced luminescence properties.