Abstract
Co(II) mononuclear complex with different coordination geometry would display various of field-induced single-ion magnet (SIM) behaviors. Here, we identify a field-induced single-ion magnet in a mononuclear complex Co(H2DPA)2·H2O (H2DPA = 2,6-pyridine-dicarboxylic acid) by the hydrothermal method. The long axial Co-O coordination bond (Co1‧‧‧O3) can be formed by Co1 and O3. Therefore, Co(II) ion is six-coordinated in a distorted elongated octahedron. AC magnetization susceptibilities show that the effective energy barrier is up to 43.28 K. This is much larger than most mononuclear Co(II). The distorted elongated octahedron caused by the axial Co-O coordination bond is responsible for the high effective energy barrier. The distribution of electron density in Co1 and O3 atoms in the long axial bond would influence the magnetic relaxation process in turn. Our work deepens the relationship between the effective energy barrier and the weak change of ligand field by long axial bonds, which would facilitate constructing SIM with high energy temperature.
Highlights
The first single-ion magnet (SIM) [Tb(III)Pc2 ] was reported in 2003 [1]
We demonstrate that the distorted octahedron caused by the long axial Co-O bond (Co1· · · O3) could play an important role in increasing the effective energy barrier of SIM, which is about 43.28 K
Note that the adjacent Co1· · · O3 distance is 2.4265 Å named as the long axial bond, which is much longer than that in the similar mononuclear Co complex
Summary
The first single-ion magnet (SIM) [Tb(III)Pc2 ] was reported in 2003 [1]. A lot of lanthanide-based SIMs were prepared and studied owing to their large single-ion magnetic anisotropies which may lead to higher energy barriers [2,3,4,5,6,7]. The magnetic anisotropy of a transition metal based complex could be greatly owned to the second-order spin–orbit coupling in the mixed states between excited and ground states [8,9]. Co(II) ion based complex show numerous coordination geometries such as two coordination [10], three coordination [11], four coordination [12,13], five coordination [14], six coordination [15,16,17], seven coordination [18] and eight coordination [19]
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