Abstract
Very high-frequency (50–715 GHz) electron paramagnetic resonance (EPR) studies of the tetranuclear Co II complex [Co(hmp)(dmb)Cl] 4 ( 1), where dmb is 3,3-dimethyl-1-butanol and hmp − is the monoanion of 2-hydroxy-methylpyridine, reveal the presence of significant zero-field-splitting (ZFS) within the ground state spin multiplet. Meanwhile, low-temperature hysteresis measurements of 1 (and related Co II 4 complexes) provide evidence for slow magnetization relaxation, suggesting that it could be a single-molecule magnet (SMM). However, EPR studies of a Zn analog of 1, doped with a small quantity of Co II, show the ground state of the Co II ions to be an effective spin S′ = 1/2 Kramers doublet with a highly anisotropic g-tensor. The question then arises as to the origin of the ZFS within the ground state spin multiplet of 1, as well as the slow magnetization relaxation. Here, we consider the effect of anisotropic exchange interactions between the effective spin S′ = 1/2 Kramers ions within the tetranuclear complex. Such exchange anisotropy arises naturally when one treats the ground state of high-spin Co II as a Kramers doublet. Our model provides an explanation for the ZFS in the ground state observed via EPR, and can also account for qualitative features observed through magnetic measurements.
Published Version
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