Solid State Characterization of One‐ and Two‐Electron Oxidized Cu^II‐salen Complexes with para‐Substituents: Geometric Structure‐Magnetic Property Relationship

Abstract

One‐ and two‐electron oxidized CuII complexes of Schiff base ligands with para‐substituted phenolate moieties were synthesized and characterized. The crystal structure of the one‐electron oxidized methylthio‐substituted complex [Cu(MeS‐salen)]SbCl6 revealed the intermolecular π‐π stacking interaction of the two phenolate moieties with those of the neighboring complex cations to form the one‐dimensional chain. Such a π‐π stacking interaction could not be detected in the two‐electron oxidized complex [Cu(MeS‐salen)](SbCl6)2 and the oxidized methoxy‐substituted complexes [Cu(MeO‐salen)](SbF6)n (n=1, 2). Magnetic study of [Cu(MeO‐salen)]SbF6 showed a weak antiferromagnetic interaction between the CuII ion and phenoxyl radical unpaired electron spins, while [Cu(MeS‐salen)]SbCl6 showed a ferromagnetism. Both of the two‐electron oxidized complexes exhibited a relatively strong magnetic interaction between the two radical electrons, while the signs of the electron spins are different.

π–π Stacking Interaction of Metal Phenoxyl Radical Complexes

“…Similar oxidation by addition of one equivalent of Th + SbCl 6 − to the solution of Ni(MeS-salen) ( 2 ) afforded the one-electron oxidized complex, [Ni(MeS-salen)]SbCl 6 ( [2]SbCl 6 ) [ 66 ]. The Cu and Ni K-edge X-ray absorption near edge structures (XANES) of these one-electron oxidized complexes showed no significant difference from that of the complexes before oxidation, whereas the sulfur K-edge XANES exhibited a noticeable increase in the pre-edge intensity of [1]SbCl 6 [ 65 , 66 , 67 , 68 ]. These results indicate that the one-electron oxidized complexes [1]SbCl 6 and [2]SbCl 6 are ligand centered oxidation species and thus can be assigned to the metal(II)-phenoxyl radical complexes.…”

“…The π orbital is assigned to the SOMO on the phenoxyl radical as whole; therefore, a SOMO–SOMO interaction can be considered in general [ 63 ]. Such a SOMO–SOMO interaction could not be observed in the crystals of metal phenoxyl radical complexes except alkylthio-phenoxyl radical species [ 39 , 40 , 64 , 65 , 66 ]. In many cases, the phenoxyl radical moiety interacted only with the counter anion weakly [ 39 , 40 , 64 ].…”

“…In many cases, the phenoxyl radical moiety interacted only with the counter anion weakly [ 39 , 40 , 64 ]. On the other hand, the alkylthio-phenoxyl radical, which is similar to the phenoxyl radical in the active form of GO, showed a significant interaction with the other phenoxyl radical by π–π stacking interaction in the solid state [ 65 ]. Furthermore, the stacking interaction between alkylthio-phenoxyl radicals exhibited a different dependence on the central metal ion [ 65 , 66 ].…”

“…Recently, the X-ray crystal structures of oxidized copper(II)- and nickel(II)-diphenolate complexes have been successfully determined. One-electron oxidized copper(II) di(methylthiophenolate) complex with a salen-type ligand, [Cu(MeS-salen)]SbCl 6 ( [1]SbCl 6 ), was prepared by reaction of Cu(MeS-salen) ( 1 ) with one equivalent of thiantrenyl radical hexachloroantimante salt (Th + SbCl 6 − ) ( Scheme 3 ) [ 65 ]. Similar oxidation by addition of one equivalent of Th + SbCl 6 − to the solution of Ni(MeS-salen) ( 2 ) afforded the one-electron oxidized complex, [Ni(MeS-salen)]SbCl 6 ( [2]SbCl 6 ) [ 66 ].…”

“…The X-ray crystal structure of [1]SbCl 6 revealed that it has half of the molecule as a crystallographically independent unit, indicating that [1]SbCl 6 has a perfect C 2 axis through the center of the ethylenediamine and the copper ion ( Figure 2 A) [ 65 ]. The results indicate that the structural features of the two phenolate moieties are identical.…”