Mixed-valence linear Co III2CoII complexes with easy-axis magnetic anisotropy: Experimental and theoretical investigation

Abstract

An in situ generated ligand formed by the Schiff base condensation of 3,5-di-tert-butylsalicylaldehyde and R(−) or S(+) 2-phenylglycinol was reacted with cobalt(II) acetate tetrahydrate, affording mixed-valence enantiomerically pure [Co^IICo^III₂(R or S-L¹)₂ (L²)₂(CO₂CH₃)₂] complexes 1-R and 1-S {where L¹ = (R) or (S)-2,4-di-tert-butyl-6-(4-hydroxo-3-phenylbut-1-en-1-yl)phenolate and L² = (R) or (S) 2-phenylglycinolate} with linear trinuclear metal cores. X-ray structural and BVS analysis revealed the linear arrangement of metal cores with the central cobalt ion in a +2 oxidation state, while the terminal cobalt ions are in a +3 oxidation state. The fitting of the DC magnetic data revealed easy-axis magnetic anisotropy with D = −58.6 cm⁻¹ (E/D = 0.257) for the Co(II) ion in 1-R. Ac magnetic susceptibility measurements confirm the field-induced dynamic magnetic behavior of 1-R with the relaxation of magnetization, which occurs through a combination of Raman and direct processes. Further CASSCF-based ab initio and NEVPT2 theoretical investigations on the X-ray structure of 1-R (or 1-S) yielded D values of −60.0 cm⁻¹ (E/D = 0.276) and −57.4 cm⁻¹ (E/D = 0.296), respectively, and helped rationalize our experimental findings.