Syntheses, crystal structures, thermal stabilities and luminescence of two new zinc phosphonates

Abstract

Two new zinc phosphonates, [(C₅H₁₄N₂)_0.5Zn₅(HO₃PCH(OH)CO₂)(O₃PCH(OH)CO₂)₃·2H₂O]·2H₂O (1) and [(C₄H₁₂N₂)Zn₂(O₃PCH(OH)CO₂)₂] (2), have been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction along with powder XRD, elemental analysis (EA), IR, and thermogravimetric analysis (TGA). In compound 1, [ZnO₆] octahedra and [ZnO₅] square-pyramids are bridged by 2-hydroxyl(phosphono)acetate with tri-, tetra-, and pentadentate coordination modes, resulting in a 3D framework possessing 1D 24-atom channels. In compound 2, 2-hydroxyl(phosphono)acetate exhibits a new tridentate coordination mode to link [ZnO₄] tetrahedrons into a 2D hybrid layer. Both 2-methylpiperazine and piperazine serve as structure-directing agents, which are encapsulated into frameworks through electrostatic interactions and hydrogen bonding. Solids 1 and 2 display purple and yellow-green emission, respectively. It is interesting that solid 1 can give off bright white, yellow and orange-red emission under different heat-treatment temperatures. Furthermore, the luminescent color of solid 1-250 can be reversibly tuned among yellow-green, purple-blue, bright white and blue-green by shifting the wavelength of excited light.