Ligand effects on the dimensionality of cyclophosphazene-based mercury(II) coordination polymers: Structures, UV–Visible absorption and thermal properties

Abstract

Herein, we have presented a new cyclotriphosphazene-functionalized molecular building block and its two new one-dimensional (1D) Hg(II) coordination polymers. Firstly, the hexakis(5-hydroxy-2-methylpyridyloxy) cyclotriphosphazene (MeHPCP) ligand was prepared and its structure was characterised by 31P{H}, 13C and 1H NMR spectroscopies, mass and FT-IR analysis. Also, its structure was determined by the single crystal X-ray diffraction technique. Next, 1D Hg(II) coordination polymers were successfully synthesized with MeHPCP using HgX2 (X = Cl, I) metal salts. The isolated white crystalline 1D Hg(II) coordination polymers, namely {[Hg(MeHPCP)(Cl)2]}n (1) and {[Hg(MeHPCP)(I)2]}n (2), were structurally characterized by elemental analysis, FT-IR spectroscopy and single crystal X-ray crystallography. Crystallographic analysis revealed that isostructural Hg(II) complexes 1 and 2 crystallize in the triclinic crystal system with the P-1 space group. In complexes 1 and 2, MeHPCP exhibited the κ2N coordination binding mode with the divalent Hg ions to form zig-zag 1D chain structures. The central Hg(II) atoms in complexes 1 and 2 have a distorted seesaw coordination geometry. The UV–Vis properties and the thermal stability of MeHPCP and its complexes (1 and 2) were also investigated. According to the thermogravimetric analysis (TGA), MeHPCP shows a higher thermal stability than 1 and 2.