Synthesis and Crystal Structure of 1D Cd-amine Coordination Polymer and Its Luminescent Properties

A novel one dimension(1D) cadmium coordination polymer {Cd(mpda)₃]·2(NO₃)}_n(1) was synthesized via refluxing a mixture of tetradentate Schiff base ligand N,N'-bis(2-pyridinylethylidene)phenylene-1,3-diamine(L) and Cd(NO₃)₂ in acetonitrile, whose structure was characterized by means of single crystal X-ray diffraction, FTIR spectroscopy, elemental analysis and proton nuclear magnetic resonance(¹H NMR). Center metal Cd(II) ion is six-coordinated by six nitrogen atoms from six different m-phenylenediamine(mpda), giving rise to aCdN₆] octahedral coordination environment. The two adjacent cadmium centers are linked by three mpda molecules leading to the construction of 1D chain structure. The crystal structure is stabilized by N-H···O hydrogen bonds to form three-dimension supramolecule. Compound 1 exhibits intense yellow luminescence in solid state at 298 K(λ_em=554 nm), which shows a blue shift at 77 K(ca. 147 nm). Additionally, fluorescence characteristics of compound 1 were investigated in different solvents(polarity: DMSO>CH₃CN>CH₃OH>CHCl₃>toluene) at 298 and 77 K. The results show that the emission peak of compound 1 in solvent exhibits a slight bathochromic shift. However, the emission peaks of compound 1 in CH₃OH and CHCl₃ are red shift compared with that in CH₃CN. It is revealed that the luminescence behavior of compound 1 depends on not only the polarity of solvent but also the hydrogen bonding properties between solvent and solute. In addition, the emission peak of compound 1 in solution shows a red shift obviously at 77 K than that at 298 K(ca. 144-159 nm), with the fluorescence lifetime increased at 77 K. The lifetime in DMSO at 77 K(τ=12.470 μs) was the longest one. The quantum yield of compoud 1 increases with increasing the polarity of solvent within a range of 1.8%-8.3%.