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, 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)]