Copper(II) complexes of N3O ligands as models for galactose oxidase: Effect of variation of steric bulk of coordinated phenoxyl moiety on the radical stability and spectroscopy.
Three N3O tripodal ligands (two pyridines, one phenol) HLMes, HLTRIP and HLNap were synthesized. The phenol ortho substituent is a mesityl, 2,4,6-tri-isopropylphenyl or 2-naphthyl group, resp. The dinuclear phenolate complexes [$μ$OH-CuII2(LMes)(HLMes)]2+ and [CuII2(LNap)2]2+ were isolated as single crystals. In [$μ$OH-CuII2(LMes)(HLMes)]2+ the Cu centers are hydroxo bridged. In [CuII2(LNap)2]2+ two phenolate groups bridge the Cu atoms. In the absence of base, mononuclear Cu(II)-phenol complexes are formed. [CuII(HLMes)(MeCN)]2+ and [CuII(HLNap)(MeCN)]2+ were structurally characterized, showing a distorted octahedral Cu ion. The phenol remains protonated and occupies one axial position, while a counterion is weakly bound on the opposite position and an MeCN mol. completes the coordination sphere. In the presence of pyridine mononuclear Cu(II) phenolate complexes [CuII(LNap)(Py)]+, [CuII(LMes)(Py)]+ and [CuII(LTRIP)(Py)]+ were obtained. The Cu(II)-phenol complexes exhibit a reversible redn. wave in the range -0.27 to -0.29 V vs. Fc+/Fc in their CV curve, which corresponds to the CuII/CuI redox couple, as well as an irreversible oxidn. wave. In the presence of pyridine a reversible oxidn. wave is obsd. at 0.09-0.13 V, assigned to the phenoxyl/phenolate redox couple. The 1-electron oxidized Cu(II)-phenoxyl complexes are mononuclear triplet species, as judged by the $Δ$MS = 2 resonance in their EPR spectra. The |D| value is estd. at 1700 MHz (axial ZFS). All these radical species exhibit an intense band at 427 nm, which combines the features of both phenoxyl $π$-$π$* and CT transitions. The stability of the radicals follows the order [CuII(LNap)(Py)]2+ {\textgreater} [CuII(LMes)(Py)]2+ {\textgreater} [CuII(LTRIP)(Py)]2+. By DFT calcns. all the phenoxyl radical species adopt a common trigonal bipyramidal geometry, wherein the phenoxyl moiety coordinates in the trigonal plane. They possess a triplet ground spin state due to orthogonality between the two SOMOs, which mainly correspond to dz2 and phenoxyl $π$ orbitals. [on SciFinder(R)]
Références
- Titre
- Copper(II) complexes of N3O ligands as models for galactose oxidase: Effect of variation of steric bulk of coordinated phenoxyl moiety on the radical stability and spectroscopy.
- Type de publication
- Article de revue
- Année de publication
- 2017
- Auteurs
- Colomban, Cedric, Philouze Christian, Molton Florian, Leconte Nicolas, and Thomas Fabrice
- Revue
- Inorganica Chim. Acta
- Pagination
- Ahead of Print
- ISSN
- 0020-1693
Soumis le 12 avril 2018