Supramolecular Coordination Complexes with 5-Sulfoisophthalic Acid and 2,5-Bipyridyl-1,3,4-Oxadiazole: Specific Sensitivity to Acidity for Cd(II) Species

A series of Cd-II Co-II, Ni-II, and Pb-II mixed-ligand coordination complexes 1-8 based on 5-sulfoisophthalic acid (H(3)sip) and the bent dipyridyl ligand 2,5-bis(3-pyridyl)-1,3,4-oxadiazole (3-bpo) or its 4-pyridyl N-donor analogue (4-bpo) have been synthesized and fully characterized by IR spectra, microanalyses, and single crystal and powder X-ray diffraction techniques. The significant pH effect on assembly of the Cd-II complexes 1-4 has been demonstrated, which leads to the formation of distinct crystalline products, whereas the Co-II, and Pb-II systems 5-8 are independent to pH condition of the synthetic reaction. Complexes 1-8 display various coordination motifs with different existing forms, conformations, and coordination modes of the organic ligands. Further, extended supramolecular networks are constructed via secondary interactions such as hydrogen-bonding and aromatic stacking. Solid-state properties of thermal stability and fluorescence for these crystalline materials are also presented.