Mixed-valent linear CoIII2CoII complexes having an 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 a mixed-valent enantiomerically pure [CoIICoIII2(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} complexes having linear trinuclear metal cores. The X-ray structure 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 an easy-axis magnetic anisotropy with D = -58.6 cm-1 (E/D = 0.257) for the Co (II) ion in 1-R. The ac magnetic susceptibility measurements confirm the field-induced dynamic magnetic behavior of 1-R with the relaxation of the 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) provide D values of -60.0 cm-1 (E/D = 0.276) and -57.4 cm-1 (E/D = 0.296), respectively, and help in rationalizing our experimental findings.