Simultaneous incorporation of both Co
II and Co
III ions within a new thioether S‐bearing phenol‐based ligand system, H
3L (2,6‐bis‐[{2‐(2‐hydroxyethylthio)ethylimino}methyl]‐4‐methylphenol) formed [Co
5] aggregates [Co
IICo
III4L
2(
μ‐OH)
2(
μ1,3‐O
2CCH
3)
2](ClO
4)
4?H
2O ( 1 ) and [Co
IICo
III4L
2(
μ‐OH)
2(
μ1,3‐O
2CC
2H
5)
2](ClO
4)
4?H
2O ( 2 ). The magnetic studies revealed axial zero‐field splitting (ZFS) parameter,
D/
hc=?23.6 and ?24.3 cm
?1, and
E/
D=0.03 and 0.00, respectively for 1 and 2 . Dynamic magnetic data confirmed the complexes as SIMs with
Ueff/kB=30 K ( 1 ) and 33 K ( 2 ), and τ
0=9.1×10
?8 s ( 1 ), and 4.3×10
?8 s ( 2 ). The larger atomic radius of S compared to N gave rise to less variation in the distortion of tetrahedral geometry around central Co
II centers, thus affecting the
D and
Ueff/kB values. Theoretical studies also support the experimental findings and reveal the origin of the anisotropy parameters. In solutions, both 1 and 2 which produce {Co
III2(
μ‐L)} units, display solvent‐dependent catechol oxidation behavior toward 3,5‐di‐
tert‐butylcatechol in air. The presence of an adjacent Co
III ion tends to assist the electron transfer from the substrate to the metal ion center, enhancing the catalytic oxidation rate.
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