Solvothermal syntheses, crystal structures and photoluminescent properties of four coordination polymers with pamoic acid and pyridine mixed ligands

Four new mixed-ligand coordination polymers, namely [Co1/2(pam)1/2·(py)2·(H2O)2]n (1), [Ni1/2(pam)1/2·(py)2·(H2O)2]n (2), [Zn1/2(pam)1/2·(py)2]n (3), and [Cd(pam)(py)2]n (4) (H2pam = pamoic acid, py = pyridine) have been synthesized under hydro(solvo)thermal conditions. X-ray single crystal structure analysis shows that 1 and 2 are isomorphic and possess a linear chain. 3 is also a linear chain without coordinated water molecules in the structure. 4 is an unusual 2D structure constructed by a binuclear cadmium building block. It appears that the chelate ligands and metal ions of the larger size favor the formation of high-dimensional structures, whereas those of the smaller size favor the formation of low-dimensional structures in the present system. The solid-state fluorescence spectra of 3, 4 and free pamoic acid show that 3 and 4 exhibit a greatly enhanced emission compared to free pamoic acid ligand.