Phenoxyl Radical Complexes of Gallium, Scandium, Iron and Manganese
Journal Article
Overview
abstract
AbstractThe hexadentate macrocyclic ligands 1,4,7‐tris(3,5‐dimethyl‐2‐hydroxybenzyl)‐1,4,7‐triazacyclononane (LH3), 1,4,7‐tris(3,5‐di‐tert‐butyl‐2‐hydroxybenzyl)‐1,4,7‐triazacyclononane (LBuH3) and 1,4,7‐tris(3‐tert‐butyl‐5‐methoxy‐2‐hydroxybenzyl)‐1,4,7‐triazacyclononane (L‐H3) form very stable octahedral neutral complexes LMIII with trivalent (or tetravalent) metal ions (GaIII, ScIII, FeIII, MnIII, MnIV). The following complexes have been synthesized: [LBuM], where M = Ga (1), Sc (2), Fe (3); [LBuMnIV]PF6 (4′); [LM], where M = Ga (1 a), Sc (2 a), Fe (3 a); [LMnIV]PF6 (4 a'); [LM], where M = Sc (2 b), Fe (3 b), MnIII (4 b); [LMnIV]2(ClO4)3(H3O)(H2O)3 (4 b'). An electrochemical study has shown that complexes 1, 2, 3, 1 a, 2 a and 3 a each display three reversible, ligand‐centred, one‐electron oxidation steps. The salts [LFeIII]ClO4 and [LGaIII]ClO4, have been isolated as stable crystalline materials. Electronic and EPR spectra prove that these oxidations produce species containing one, two or three coordinated phenoxyl radicals. The Mössbauer spectra of 3 a and [3 a]+ show conclusively that both compounds contain high‐spin iron(III) central ions. Temperature‐dependent magnetic susceptibility measurements reveal that 3 a has an S = 5/2 and [3a]+ an S = 2 ground state. The latter is attained through intramolecular antiferromagnetic exchange coupling between a high‐spin iron(III) (S1 = 5/2) and a phenoxyl radical (S2 = 1/2) (H = ‐ 2JS1S2; J = ‐ 80 cm−1). The manganese complexes undergo metal‐ and ligand‐centred redox processes, which were elucidated by spectroelectrochemistry; a phenoxyl radical MnIV complex [MnIVL]2+ is accessible.
