Département de chimie moléculaire

The two tetradentate salen-type ligands I (H2L) and II [R = Me (H2LMe)] afford the slightly distorted square-planar low-spin NiII complexes [Ni(L)] (1) and [Ni(LMe)] (2), which comprise two coordinated phenolate groups. Complex 1 was electrochem. oxidized into 1+, which contains a coordinated phenoxyl radical, with a contribution from the Ni orbital. In the presence of pyridine, 1+ is converted into 1Py+, an octahedral phenolate Ni(III) complex with two pyridines axially coordinated; an intramol. electron transfer (valence tautomerism) is promoted by the geometrical changes, from square planar to octahedral, around the metal center. The tetradentate ligand H2LMe, in the presence of pyridine, and the hexadentate ligand II [R = 2-pyridylmethyl (H2LPy)] in CH2Cl2 afford, resp., the octahedral high-spin NiII complexes 2Py and [Ni(LPy)] (3), which involve two equatorial phenolates and two axially coordinated pyridines. At 100 K, the 1-electron-oxidized product 2Py+ comprises a phenoxyl radical ferromagnetically coupled to the high-spin NiII ion, with large zero-field splitting parameters, while 3+ involves a phenoxyl radical antiferromagnetically coupled to the high-spin NiII ion. [on SciFinder(R)]