Synthesis, characterization, spectroscopic and electrochemical studies of new thioether ligated octahedral low-spin cobalt(II) complex: Oxidative cleavage of C-S bond

Abstract

The reaction of cobalt (II) acetate tetrahydrate with dithiaalkyl substituted arylazo-oxime ligand HON=C(Ph)N=NC₆H₄S(CH₂)₂SC₆H₄N=NC(Ph)=NOH (H₂PhL).<b>1</b>, affords a thioether ligated octahedral low-spin [Co^II (PhL)].<b> 2</b>, (<i>d</i>^{<span style="mso-bidi-font-style:italic">7</span>}<i>, </i>t_2g⁶e¹ , <i>S </i>= 1/2) with CoN₄S₂ coordination. The room temperature magnetic moment of solid [Co^II (PhL)] is 1.88 <i>μ</i>_B. The low-spin configuration is further authenticated by it s eight line EPR spectra (<i>g </i>= 2.02, <i>A </i>= 31<i>G</i>) in frozen acetonitrile (77 K). The complex displays a quasi-reversible (Δ<i>E</i>_p = 90 mV) one-electron cyclic response in acetonitrile at 0.08 V versus saturated calomel electrode. The response is assigned to the [Co^II (PhL)]/[ Co^II (PhL)t oxidation. Moreover, the bivalent [Co^II (Ph L)], <b>2</b>, undergoes an oxidative cleavage of the C-S bond to afford parent [Co^II (PhL)ClO₄]. <b>3</b>, and transformed [Co^II (PhLʹ)(PhLʹʹ)], complexes in their trivalent state. In CDCl₃, the splitting of the vinylic protons of [Co^II (PhLʹ)(PhLʹʹ)], <b>4</b>. appears at δ5.85 (dd), 5.66 (dd) and 5.58 (dd), respectively (dd =doublet of doublet). All complexes have been characterized with the help of C, H, N analysis. FAB mass, cyclic voltammetry, spectroscopic techniques (UV-vis,¹H NMR and EPR) and magnetic studies.