Synthesis, crystal structure and magnetic properties of octanuclear Ni4Ln4 complexes constructed using a Schiff base ligand and di-2-pyridyl ketone

Abstract

Synthesis of 3d–4f single molecule magnets (SMMs) with novel topologies and exploration of the magnetic relaxation mechanism of SMMs have continuously received considerable attention because high performance SMMs could be obtained. In this work, we selected N-3-methoxysalicylidene-2-amino-3-hydroxypyridine (H₂L) and di-2-pyridyl ketone (dpk) for reaction with Ni(NO₃)₂·6H₂O, Dy(NO₃)₃·5H₂O and trimethylamine in a CH₃OH solution, and a novel Ni₄Dy₄ complex, [Ni₄Dy₄(L)₆(L′)₂{(py)₂C(OCH₃)O}₂(μ₃-CO₃)₂(CH₃OH)₂]·10CH₃OH·13H₂O (1, (py)₂C(OCH₃)(OH) = the hemiacetal form of dpk), was obtained. The magnetic diluted complex, [Ni₄Y_3.91Dy_0.09(L)₆(L′)₂{(py)₂C(OCH₃)O}₂(μ₃-CO₃)₂(CH₃OH)₂]·10CH₃OH·12H₂O (2), and the Y analogue of 1, [Ni₄Y₄(L)₆(L′)₂{(py)₂C(OCH₃)O}₂(μ₃-CO₃)₂(CH₃OH)₂]·10CH₃OH·11H₂O (3), were also obtained. The carbonate ions in 1–3 were formed by spontaneous fixation of atmospheric CO₂. Structural analysis revealed that the metallic core in 1 can be viewed as a Ni₂Dy₂ butterfly connecting two NiDy subunits on each side. To our knowledge, the structural topologies of 1–3 were not reported previously. The magnetic susceptibilities of 3 were fitted by PHI, indicating that the magnetic coupling between Ni1 and Ni1a in the “Ni₂Y₂ butterfly” subunit of 3 is ferromagnetic. Alternating-current (ac) susceptibility studies revealed that 1–2 exhibit single molecule magnet behavior under a zero dc field.