Entrapment of a Pseudo‐Tetrahedral CoII Center by Thioether Sulfur Bound {Co2(μ‐L)} Fragments: Synthesis, Field‐Induced Single‐Ion Magnetism and Catechol Oxidase Mimicking Activity. Issue 21 (10th October 2019)

• Record Type: Journal Article
• Authors: Das, Manisha; Basak, Dipmalya; Trávníček, Zdeněk; Vančo, Ján; Ray, Debashis
• Is Part Of: Chemistry, an Asian journal. Volume 14:Issue 21(2019)
• Page Start: 3898
• Page End: 3914
• Publication Date: 2019-10-10
• Subjects: catecholase activity -- cobalt -- magnetic anisotropy -- single-molecule magnets -- thioether ligand; Chemistry -- Periodicals; 540.5
• DOI: 10.1002/asia.201901109
• Languages: English
• ISSNs: 1861-4728

Abstract

Abstract: Simultaneous incorporation of both Co II and Co III ions within a new thioether S‐bearing phenol‐based ligand system, H3 L (2, 6‐bis‐[{2‐(2‐hydroxyethylthio)ethylimino}methyl]‐4‐methylphenol) formed [Co5 ] aggregates [Co II Co III 4 L2 ( μ ‐OH)2 ( μ 1, 3 ‐O2 CCH3 )2 ](ClO4 )4 ⋅H2 O (1 ) and [Co II Co III 4 L2 ( μ ‐OH)2 ( μ 1, 3 ‐O2 CC2 H5 )2 ](ClO4 )4 ⋅H2 O (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 τ0 =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 III 2 ( 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. Abstract : The magnetic properties and catalytic activity of "mixed‐valent‐mixed‐geometry" [Co5 ] aggregates containing a pseudo ‐tetrahedral Co II has been discussed. The use of the larger donor atom S leads to less variation in D and Ueff /kB values in comparison to N. Catalytically active fragments show catechol oxidase behavior with assistance from a "spectator" Co III center.