PHENOXYL RADICAL COMPLEXES OF GALLIUM, SCANDIUM, IRON AND MANGANESE

The hexadentate macrocyclic ligands 1,4,7-tris(3,5-dimethyl-2-hydroxyb enzyl)-1 ,4,7-triazacyclononane ((LH3)-H-CH3), ert-butyl-2-hydroxybenz yl)-1,4,7-triazacyclononane ((LH3)-H-Bu) and 4,7-tris(3-tert-butyl-5-m ethoxy-2-hydroxybenzyl)-1 ,4,7-triazacyclononane (L-OCH3- H,) form ver y stable octahedral neutral complexes LMIII with trivalent (or tetrava lent) metal ions (Ga-III, Sc-III, Fe-III, Mn-III, Mn-IV). The followin g complexes have been synthesized: [(LM)-M-Bu], where M = Ga (1), Sc ( 2), Fe (3); [(LMnIV)-Mn-Bu]PF6 (4'); [(LM)-M-OCH3], where M = Ga (1a), Sc (2a), Fe (3a); [(LMnIV)-Mn-OCH3]PF6 (4a'); [(LM)-M-CH3], where M = Sc (2b), Fe (3b), Mn-III (4b); [(LMnIV)-Mn-CH3](2)(ClO4)(3)(H3O)(H2O) (3) (4b'). An electrochemical study has shown that complexes 1, 2, 3, 1a, 2a and 3a each display three reversible, ligand-centred, one-elect ron oxidation steps. The salts [(LFeIII)-Fe-OCH3]ClO4 and [(LGaIII)-Ga -OCH3]ClO4 have been isolated as stable crystalline materials. Electro nic and EPR spectra prove that these oxidations produce species contai ning one, two or three coordinated phenoxyl radicals. The Mossbauer sp ectra of 3 a and [3 a](+) show conclusively that both compounds contai n high-spin iron(III) central ions, Temperature-dependent magnetic sus ceptibility measurements reveal that 3a has an S = 5/2 and [3a](+) an S = 2 ground state. The latter is attained through intramolecular anti ferromagnetic exchange coupling between a high-spin iron(III) (S-1 = 5 /2) and a phenoxyl radical (S-2 = 1/2) (H = - 2JS(1)S(2); J = - 80 cm( -1)). The manganese complexes undergo metal- and ligand-centred redox processes, which were elucidated by spectroelectrochemistry; a phenoxy l radical Mn-IV complex [(MnLOCH3)-L-IV](2+) is accessible.