Entrapment of a Pseudo‐Tetrahedral Co^II Center by Thioether Sulfur Bound {Co₂(μ‐L)} Fragments: Synthesis, Field‐Induced Single‐Ion Magnetism and Catechol Oxidase Mimicking Activity

Abstract

Simultaneous incorporation of both Co II and Co III ions within an ew thioether S-bearing phenol-based ligand system, H 3 L( 2,6-bis-[{2-(2-hydroxyethylthio)ethylimino}methyl]-4-methylphenol) formed [Co 5 ]a ggregates [Co II Co III 4 L 2 (m-OH) 2 (m 1,3 -O 2 CCH 3 ) 2 ](ClO 4 ) 4 ·H 2 O( 1)a nd [Co II Co III 4 L 2 (m-OH) 2 (m 1,3 -O 2 CC 2 H 5 ) 2 ](ClO 4 ) 4 ·H 2 O( 2). The magnetic studies revealed axial zero-field splitting (ZFS) parameter, D/hc = À23.6 and À24.3 cm À1 ,a nd E/D = 0.03 and 0.00, respectively for 1 and 2.D ynamic magnetic data confirmed the complexes as SIMs with U eff /k B = 30 K( 1)a nd 33 K( 2), and t 0 = 9.1 10 À8 s( 1), and 4.3 10 À8 s( 2). The larger atomic radius of Sc ompared to Ng ave rise to less variation in the distortion of tetrahedral geometry around central Co II centers, thus affecting the D and U eff /k B values. Theoretical studies also support the experimental findings and reveal the origin of the anisotropy parameters. In solutions, both 1 and 2 whichp roduce {Co III 2 (m-L)} units, display solvent-dependent catechol oxidation behavior toward3 ,5-di-tert-butylcatechol in air.T he presence of an adjacentC o III ion tends to assist the electron transfer from the substratet ot he metal ion center, enhancing the catalytic oxidationr ate.[a] M. Figure 11. Time dependent UV-vis spectral changes for Complexes 1 and 2 (conc. % 1 10 À5 mol L À1 )u pon additiono fe xcess of (100 fold) 3,5-DTBCH 2 (conc. % 1 10 À3 mol L À1 )i nM eOH (a and b) and in MeCN (c and d) at 298 K.