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Published on: September 23, 2021
Monomer-to-trimer comparison of slow magnetic relaxation in weakly antiferromagnetically coupled triangular Co(II)
Jiawen Zhong1, Mengxing Cui1, Takefumi Yoshida2
1School of Chemical Science and Engineering, Tongji University, Siping Road 1239, Shanghai, 200092, P. R. China. cuimengxing@tongji.edu.cn.
Abstract:
We report a comparative study of slow magnetic relaxation in two structurally related Co(II) complexes designed to clarify how triangular topology and geometric spin frustration reshape single-molecule magnet behavior. A mononuclear complex 1, [Co(pdms)(py)2] (H2pdms = 1,2-bis(methanesulfonamido)benzene, py = pyridine) behaves as an isolated and distorted tetrahedral [CoN4] single-ion reference. A star-shaped trinuclear analogue 2, [Co3(L)(py)6] (H6L = 2,3,6,7,10,11-hexakis(methanesulfonamido)triphenylene), was constructed by anchoring three "1-like" Co(II) units onto a rigid triphenylene-based H6L ligand to enforce a Co3-triangular arrangement. The susceptibility reveals markedly different magnetic parameters, with 1 showing stronger axial anisotropy (DCo = -21.3 cm-1) and 2 exhibiting reduced anisotropy (DCo = -8.4 cm-1) together with antiferromagnetic interactions (CW = -9.4 K, JCo-Co = -1.88 K). Field-induced ac susceptibility confirms slow magnetic relaxation for both complexes; however, 1 relaxes more slowly than 2 at the same temperature, resulting in an effective energy barrier Ueff = 37.1 cm-1 for 1 and Ueff = 3.7 cm-1 for 2. This contrast demonstrates that trimerization does not necessarily enhance the SMM performance. The faster relaxation in 2 is more conservatively attributed to weak antiferromagnetic exchange, closely spaced exchange-coupled spin states, and the triangular Co3 topology, while geometric frustration is discussed only as a possible contributing factor rather than a uniquely established origin.
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