Synthesis, crystal structures and magnetic properties of two Ni-Dy heterometallic complexes with the structural topologies regulated by employing different Schiff base ligands

Abstract

Regulation of the structural topologies of single molecule magnets (SMMs) is one of the most important approach for enhancing their SMM performance. In this work, we first obtained a Ni2Dy trinuclear complex, [Ni2Dy(Hhmmp)2{(py)2CO2}(CH3COO)2]OH (1, H2hmmp = 2-[(2-hydroxyethylimino)methyl]-6-methoxyphenol, (py)2C(OH)2 = the gem-diol form of di-2-pyridyl ketone (dpk)) by employing H2hmmp and dpk reacting with Dy(NO3)3·5H2O and Ni(CH3COO)2·4H2O in the MeCN solution containing triethylamine. However, when H2hmmp, triethylamine and MeCN in the reaction system of 1 were replaced by 2-(((2-hydroxy-3-methoxyphenyl)methylene)amino)-2-(hydroxymethyl)-1,3-propanediol (H4L), N(Me)4OH·5H2O and the mixture of MeCN and N,N-dimethylformamide (DMF), a Ni2Dy2 complex, [Ni2Dy2(HL)2{(py)2CO(OH)}2(CH3COO)2]·2H2O (2), was obtained. Structural analysis revealed that two NiII and one DyIII in 1 formed a “V-shaped” topology, while two NiII and two DyIII ions in 2 formed a butterfly-like topology with Ni and DyIII ions occupied on the body positions and the wing positions, respectively. Additionally, the coordination geometries of DyIII ion in 1 and 2 square antiprism geometry (D4d) and capped octahedron (C3v), respectively. Magnetic investigation indicated that 1 exhibits obviously slow magnetic relaxation behavior, with an energy barrier Ueff of ∼6 K. The orientations of the magnetic anisotropy of DyIII in 1 and 2 were estimated by Magellan software; the results indicate that few coordination atoms were located on the equatorial plane of DyIII in 1 and 2, which result in 1 and 2 exhibiting poor SMM performance.