Acta Phys. -Chim. Sin. ›› 2018, Vol. 34 ›› Issue (7): 812-817.doi: 10.3866/PKU.WHXB201801086

Special Issue: 原子水平上精确控制纳米簇和纳米粒子

• ARTICLE • Previous Articles     Next Articles

Construction and NIR Luminescence Properties of Zn-Ln Rectangular Nanoclusters

Dongmei JIANG,Le BO,Ting ZHU,Junbin TAO,Xiaoping YANG*()   

  • Received:2017-12-14 Published:2018-03-26
  • Contact: Xiaoping YANG E-mail:xpyang@wzu.edu.cn
  • Supported by:
    the National Natural Science Foundation of China(21771141)

Abstract:

Heterometallic d-4f nanoclusters are currently of interest due to their potential use in material science and as probes in biology. Self-assembly by metal-ligand coordination is one of the most efficient processes that organize individual molecular components into nanosized species. However, for lanthanide-based self-assemblies, their stoichiometries and structures are difficult to control during synthesis, because the Ln(Ⅲ) ions often display high and variable coordination numbers. As a result, the structures of lanthanide complexes are commonly influenced by a variety of factors, such as the type of metal ions, the formation of ligands, and the nature of counter anions. In this article, two Zn-Ln nanoclusters [Ln2Zn2L2(OAc)6] (Ln = Yb (1) and Er (2)) were prepared using a new long Schiff base ligand with a Ph(CH2)Ph backbone. These nanoclusters show interesting rectangular-like structures. The long Schiff base ligand displays a "stretched" configuration and is bound to the metal ions through its N and phenoxide and methoxy O atoms. As a result, large clusters (0.7 nm × 1.1 nm × 2.2 nm for 1) were formed. In the crystal structures of 1 and 2, each Ln3+ ion and its closer Zn2+ ion are linked by one OAc- anion and phenolic oxygen atoms of two long Schiff base ligands, forming a ZnLn unit. Two such ZnLn units are then bridged by two Schiff base ligands to form the nano-rectangular structures. Energy dispersive X-ray spectroscopy (EDX) analyses of the clusters indicate that the molar ratio of Zn : Ln is about 1 : 1, in agreement with their crystal structures. Thermogravimetric analyses show that the clusters lose about 5% of the weight when heated to below 100 ℃. Melting point measurements show that the clusters are thermodynamically stable. Upon excitation of the ligand-centered absorption bands, 1 and 2 exhibit the NIR luminescence of Yb3+ and Er3+, respectively. The clusters show two excitation bands from 250 to 500 nm, in agreement with their absorption spectra, confirming that energy transfer occurs from the Zn/L centers to Ln3+ ions. These results indicate that the chromogenic Zn/L components in these nanoclusters can act as efficient sensitizers for lanthanide luminescence. The efficiencies of the energy transfer from Zn/L-centers to Yb3+ is higher than that to Er3+, being 75.71% and 25.00% for 1 and 2, respectively. These results provide new insights into the design of polynuclear nanoclusters with interesting luminescence properties.

Key words: Construction, Zn-Ln nanocluster, Schiff base ligand, Structure, Luminescence

MSC2000: 

  • O641