Effect of pH on the construction of Cd coordination polymers involving the 1,1'-[1,4-phenylenebis(methylene)]bis(3,5-dicarboxylatopyridinium) ligand.

Changing the pH value of a reaction system can result in polymers with very different compositions and architectures. Two new coordination polymers based on 1,1'-[1,4-phenylenebis(methylene)]bis(3,5-dicarboxylatopyridinium) (L), namely catena-poly[[[tetraaquacadmium(II)]-μ-1,1'-[1,4-phenylenebis(methylene)]bis(3,5-dicarboxylatopyridinium)] 1.66-hydrate], {[Cd(CHNO)(HO)]·1.66HO}, (I), and poly[{μ-1,1'-[1,4-phenylenebis(methylene)]bis(3,5-dicarboxylatopyridinium)}cadmium(II)], [Cd(CHNO)], (II), have been prepared in the presence of NaOH or HNO and structurally characterized by single-crystal X-ray diffraction. In polymer (I), each Cd ion is coordinated by two halves of independent L ligands, forming a one-dimensional chain structure. In the crystal, these chains are further connected through O-H...O hydrogen bonds, leading to a three-dimensional hydrogen-bonded network. In polymer (II), each hexadentate L ligand coordinates to six Cd ions, resulting in a three-dimensional network structure, in which all of the Cd ions and L ligands are equivalent, respectively. The IR spectra, thermogravimetric analyses and fluorescence properties of both reported compounds were investigated.