High-frequency EPR study on Cu$_4$Cu- and Co$_4$Co-metallacrown complexes

High-frequency/high-field electron paramagnetic resonance studies on two homo-nuclear 12-MC-4 metallacrown complexes Cu$_4$Cu and Co$_4$Co are presented. For Cu$_4$Cu, 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 Co$_4$Co, we find a m$_S$ = $\pm$3/2 ground state with $g=2.66$. The data suggest large anisotropy $D$ of negative sign.