Syntheses, Structures, Luminescence, and Magnetic Properties of a Series of Novel Coordination Polymers Constructed by Nanosized [Ln₈Fe₄] Rings

Abstract

A total of five three-dimensional Ln-Fe coordination polymers (CPs) [(CH 3 ) 2 NH][(CH 3 ) 2 NH 2 ][Ln 2 Fe(SO 4 ) 4 (L)]·3H 2 O (Ln = Eu, 1; Dy, 2; Gd, 3; Sm, 4; Er, 5; H 2 L = tartaric acid) have been successfully synthesized under solvothermal conditions and characterized by infrared spectroscopy, thermogravimetric analysis, elemental analyses, luminescence, and magnetic properties. Structural analysis indicates that the frameworks of 1 – 5 are constructed from novel [Ln 8 Fe 4 ] rings. In the strcutures of 1 – 5, Ln III and Fe III ions interconnect through O donors of sulfate anions to generate a one-dimensional chain, and the adjacent chains are joined together by ligand [L] 2– to form a two-dimensional zonary plane, which is further bridged by ligand [L] 2– to give a new topology and named as “ Xhd 1 ”. Magnetic properties of 2 and 3 were investigated using variable temperature magnetic susceptibility, and weak ferromagnetic exchange between the Fe III and Ln III ions has been established for the Gd derivative. Meanwhile, we also studied luminescence spectra and luminescence lifetimes of 1 and 4 in the solid state at room temperature. The luminescence lifetime of 1 is 0.98 ms, which is significantly longer than the values in the reported Eu 3+ coordination polymers.