Structures, fluorescence, and superoxide radical scavenging activities of two cd–Ln (Ln = Gd, Er) coordination polymers with an open-chain ether Schiff base and isonicotinate

Abstract

Two Cd–Ln coordination polymers (CPs), with the open-chain ether Schiff base bis(5-bromine-3-methoxysalicylidene)-3-oxapentane-1,5-diamine (H2L), {[CdLnL(OAc)(NO3)(CH3OH)(isonicotinate)]·(3CH2Cl2)}n (Ln = Gd (1) and Er (2)), have been synthesized by the interfacial diffusion method. The structure analysis reveals that both CPs 1 and 2 are infinite one-dimensional zigzag coordination polymers, which are formed by isonicotinate bridging CdLnL cluster units. The fluorescence properties of H2L, 1 and 2 in the solid-state were studied. Compared with the free H2L, the fluorescence peaks of the two Cd–Ln CPs have undergone a significant blue shift (about 80 nm) and enhancement. This is due to the increased rigidity of the ligand after coordination of the metal ions with the ligand, which reduces the energy loss of thermal vibration. The fluorescence enhancement of 1 is greater than that of 2, which may be caused by the lanthanide contraction. Moreover, the results of experiments in vitro indicate that H2L, 1 and 2 have good ability to scavenge superoxide radical and that 1 and 2 are higher than free H2L, where their IC50 value is in the range 12.5–21.4 μM.