Synthesis and crystal structure of 1D Cd-amine coordination polymer and its luminescent properties

Abstract

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 a [CdN6] 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 %.