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

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.