Cd-Ln (Ln = Pr, Sm, Yb and Nd) heteronuclear complexes based on the linear chain ether Schiff base: Structural regulation and fluorescence properties

Abstract

Four structurally different Cd-Ln heteronuclear complexes based on the linear chain ether Schiff base ligand (bis(3-methoxysalicylidene)-3-oxapentane-1,5-diamine (H2L) and the co-ligands 4,4′-bipyridine (bipy) or isonicotinate (IN), with composition [PrCd2L2(CH3COO)2](NO3)·CH2Cl2 (1), {[SmCdL(bipy)(NO3)3]·CH2Cl2·CH3CH2OH}n (2), [YbCdL(IN)(NO3)(CH3COO)]n (3) and {[Nd2Cd2L2(IN)2(NO3)2(CH3OH)2(CH3COO)](NO3)}n (4), have been synthesized by interfacial diffusion methods. Structural regulation is achieved by changes in the co-ligands or Ln(III) ions of different radii: Single crystal X-ray analysis determined that 1 is a trinuclear cluster with the Pr(III) ion as a joint bridging of two CdL coordination units; 2 and 3 are both infinite one-dimensional zigzag coordination polymers consisting of CdLnL secondary units through coordination bridging bipy or IN; 4 is a two-dimensional graphene laminate structure formed by two types of CdNdL secondary units bridged by both IN and acetate simultaneously. In the solid state, the complexes 1–4 all exhibit fluorescence peaks based on H2L with blue shift and enhancement. The order of fluorescence peaks intensity of the complexes in N,N-dimethylformamide (DMF) solution is consistent with that in the solid state. Moreover, the corresponding characteristic emissions of Sm(III) ion in complex 2 can be observed in the fluorescence spectra in either solid state and DMF solution, indicating that [CdL] unit is suitable for the sensitization of Sm(III) ion.