Département de chimie moléculaire

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, respectively. The dinuclear copper(II)-phenolate complexes [ÎŒOH-Cu2II(LMes)(HLMes)]2+ and [Cu2II(LNap)2]2+ were isolated as single crystals. In [ÎŒOH-Cu2II(LMes)(HLMes)]2+ the two copper centers are bridged by a hydroxo unit. In [Cu2II(LNap)2]2+ two phenolate groups bridge the copper atoms. In the absence of base the mononuclear copper(II)-phenol complexes are formed. The complexes [CuII(HLMes)(CH3CN)]2+ and [CuII(HLNap)(CH3CN)]2+ were structurally characterized, showing a distorted octahedral copper ion. The phenol remains protonated and occupies one axial position, while a counter ion is weakly bound on the opposite position and an acetonitrile molecule completes the coordination sphere. In the presence of pyridine mononuclear copper(II)-phenolate complexes of general formula [CuII(LNap)(Py)]+, [CuII(LMes)(Py)]+ and [CuII(LTRIP)(Py)]+ are obtained. The copper(II)-phenol complexes exhibit a reversible reduction wave in the range −0.27 to −0.29V vs. Fc+/Fc in their CV curve, which corresponds to the CuII/CuI redox couple, as well as an irreversible oxidation wave. In the presence of pyridine a reversible oxidation wave is observed at 0.09–0.13V. It is assigned to the phenoxyl/phenolate redox couple. The one-electron oxidized copper(II)-phenoxyl complexes are mononuclear triplet species, as judged by the ΔMS=2 resonance in their EPR spectra. The |D| value is estimated at 1700MHz (axial ZFS). All these radical species exhibit an intense band at 427nm, which combines the features of both phenoxyl π–π∗ and CT transitions. The stability of the radicals follows the order [CuII(LNap)(Py)]2+>[CuII(LMes)(Py)]2+>[CuII(LTRIP)(Py)]2+. By DFT calculations we show that 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 the orthogonality between the two SOMOs, which mainly correspond to dz2 and phenoxyl π orbitals.