Manipulating a series of Ln-based helix chains or dinuclear complexes by designing two types of Schiff-based ligands: Structure and magnetic properties

Abstract

As an important means of regulating ligands, steric hindrance effect is always the first choice to construct structures. It is rare to assemble complexes with different topological and structural types by increasing or decreasing the steric hindrance of ligands and to regulate their properties. Here, we successfully obtained two types of lanthanide structures [Ln(H2L1)(NO3)3]n (1: Dy; 2: Gd, H2L1 ​= ​6,6'-((1E,1′E)-((2,2-dimethylpropane-1,3-diyl)bis(azanylylidene))bis(methanylylidene))bis(2-methoxyphenol)) and [Ln2(H2L2)3(NO3)6]·(CH3CN)x·(CH3OH)y (3: Dy, x ​= ​3, y ​= ​0; 4: Gd, x ​= ​y ​= ​2, H2L2 ​= ​6,6'-((1E,1′E)-((2,2-dimethylpropane-1,3-diyl)bis(azanylylidene))bis(methanylylidene))bis(2-ethoxyphenol)), which are controlled by ligands with the steric hindrance effect. For the all structures, the ligands are distorted when they coordinate with lanthanide ions, which make the ligands form helical structures around Ln(III) ions. For chains 1 and 2, there is a single twisted ligand bridging to form a one-dimensional spiral chain between the Ln(III) ion and the Ln(III) ion. But for complexes 3 and 4, there is a helical dinuclear structure formed by the cross-bridging of a double twisted ligand between the Ln(III) ion and the Ln(III) ion. AC magnetic susceptibilities show that chain 1 is a single-molecule magnet (SMM), which exhibits obviously frequency dependent behavior with the energy barriers of 39.6 (3) K and 44.6 (5) K, but complex 3 shows field-induced single-molecule magnetic behavior. The magnetocaloric effects (MCEs) show that chain 2 has bigger value of S than that of complex 4.