Synthesis, characterization, crystal structure determination and luminescence study of new linear coordination polymers based on Mercury(II), Cadmium(II) and 4,7-phenanthroline ligand

Abstract

Three novel coordination polymers containing Hg(II) and/or Cd(II) with 4,7-phenanthroline ligand (4,7-phen) have been synthesized and structurally characterized by single-crystal X-ray diffraction. Complexes [Hg(η2-4,7-phen)Br2]n (1), [Hg(η2-4,7-phen)I2]n (2) and [Cd(η2-4,7-phen)I2]n (3) were prepared from the reaction of one equivalent of 4,7-phenanthroline ligand with one equivalent of HgBr2 (1), HgI2 (2) and CdI2 (3), in methanol, respectively. Suitable crystals of title compounds were obtained for X-ray diffraction measurement by methanol diffusion into a DMSO solution. All compounds have linear polymeric structures which extend parallel to the c axis and contain Hg(II) and Cd(II) centers coordinated by two bridging 4,7-phenanthroline ligands, and two coordinated halogen molecules, completing the Hg(II) and Cd(II) coordination spheres, and resulting in a distorted tetrahedral geometry. Furthermore, π-π (in 1–3) and M-I⋯π (in 2 and 3) interactions play crucial role on stabilization of the crystal packing. The luminescence properties of the free ligand as well as the complexes 1–3 were investigated in solution. Thermal stabilities of these complexes were also studied by TGA/DTA analyses.