High-frequency EPR study on Cu4Cu- and Co4Co-metallacrown complexes

doi:10.1016/j.jmmm.2019.01.038

Journal of Magnetism and Magnetic Materials

Volume 477, 1 May 2019, Pages 340-343

https://doi.org/10.1016/j.jmmm.2019.01.038 Get rights and content

Highlights

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First high frequency/high field EPR study on Cu₄Cu and Co₄Co is presented.
•
Cu₄Cu shows S = 1/2 spin ground state and axial type g-anisotropy
•
Co₄Co features S = 3/2 ground state and D < 0.

Abstract

High-frequency/high-field electron paramagnetic resonance studies on two homonuclear 12-MC-4 metallacrown complexes Cu₄Cu and Co₄Co are presented. For Cu₄Cu, our data imply axial-type g-anisotropy with $g_{x} = 2.03 \pm 0.01$ , $g_{y} = 2.04 \pm 0.01$ , and $g_{z} = 2.23 \pm 0.01$ , yielding $g = 2.10 \pm 0.02$ . No significant zero field splitting (ZFS) of the ground state mode is observed. In Co₄Co, we find a $m_{S} = \pm 3 / 2$ ground state with $g = 2.66$ . The data suggest large anisotropy D of negative sign.

Section snippets

Introduction and experiment

Metallacrowns are coordination compounds including metal ions where a repeating sequence, i.e., [–M–O–N–], forms macroscopic rings. [1] The characteristic rings of regular metallacrowns involve oxygens pointing towards the core of the cycle, thereby offering coordination positions of central cations. The class of 12-MC-4 studied at hand comprises 12 atoms in the planar square cycle, i.e., four of which being metal ions, with an additional metal ion in slightly off-plane center site. Here, we

Discussion and summary

Powder HF-EPR spectra presented here confirm the $S = 1 / 2$ ground state in Cu₄Cu. From previous susceptibility data, the exchange couplings $J_{1} = - 155.2 {cm}^{- 1}$ between the center and corner spins, and $J_{2} = - 92.3 {cm}^{- 1}$ between the nearest neighbor corner spins as well as $g = 2.16$ had been deduced [7], [1]. The HF-EPR data presented at hand imply axial-type g-anisotropy with $g_{x} = 2.03 \pm 0.01$ , $g_{y} = 2.04 \pm 0.01$ , and $g_{z} = 2.23 \pm 0.01$ , yielding $g = (g_{x} + g_{y} + g_{z}) / 3 = 2.10 \pm 0.02$ , which is a typical value in Cu complexes [5], [6]. This

Acknowledgement

C. Koo acknowledges the support from the Deutsche Forschungsgemeinschaft under project number KO5480/1-1.

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Research articlesHigh-frequency EPR study on Cu4Cu- and Co4Co-metallacrown complexes

Highlights

Abstract

Section snippets

Introduction and experiment

Discussion and summary

Acknowledgement

Coord. Chem. Rev.

J. Magn. Reson.

Polyhedron

Dalton Trans.

Inorg. Chem.

Research articles
High-frequency EPR study on Cu₄Cu- and Co₄Co-metallacrown complexes