title: Phenoxyl radical complexes of gallium, scandium, iron and manganese.
abstract: The hexadentate macrocyclic ligands 1,4,7-tris(3,5-dimethyl-2-hydroxybenzyl)-1,4,7-triazacyclononane (L CH 3H3 ), 1,4,7-tris(3,5-di-tert-butyl-2-hydroxybenzyl)-1,4,7-triazacyclononane (L(Bu) H3 ) and 1,4,7-tris(3-tert-butyl-5-methoxy-2-hydroxybenzyl)-1,4,7-triazacyclononane (L OCH 3-H3 ) form very stable octahedral neutral complexes LM(III) with trivalent (or tetravalent) metal ions (Ga(III) , Sc(III) , Fe(III) , Mn(III) , Mn(IV) ). The following complexes have been synthesized: [L(Bu) M], where M = Ga (1), Sc (2), Fe (3); [L(Bu) Mn(IV) ]PF6 (4'); [L OCH 3M], where M = Ga (1 a), Sc (2 a), Fe (3 a); [L OCH 3Mn(IV) ]PF6 (4 a'); [L CH 3M], where M = Sc (2 b), Fe (3 b), Mn(III) (4 b); [L CH 3Mn(IV) ]2 (ClO4 )3 (H3 O)(H2 O)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 [L OCH 3Fe(III) ]ClO4 and [L OCH 3Ga(III) ]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 = - 2JS1 S2 ; J = - 80 cm(-1) ). The manganese complexes undergo metal- and ligand-centred redox processes, which were elucidated by spectroelectrochemistry; a phenoxyl radical Mn(IV) complex [Mn(IV) L OCH 3](2+) is accessible.
authors.affiliation: Max-Planck-Institut für Strahlenchemie, Stiftstrasse 34-36 D-45470 Mülheim an der Ruhr (Germany), Fax: Int. code +(208)306-3952, e-mail: wieghardt@mpi-muelheim.mpg.de.
authors.forename: B
authors.initials: B
authors.lastname: Adam
authors.forename: E
authors.initials: E
authors.lastname: Bill
authors.forename: E
authors.initials: E
authors.lastname: Bothe
authors.forename: B
authors.initials: B
authors.lastname: Goerdt
authors.forename: G
authors.initials: G
authors.lastname: Haselhorst
authors.forename: K
authors.initials: K
authors.lastname: Hildenbrand
authors.forename: A
authors.initials: A
authors.lastname: Sokolowski
authors.forename: S
authors.initials: S
authors.lastname: Steenken
authors.forename: T
authors.initials: T
authors.lastname: Weyhermüller
authors.forename: K
authors.initials: K
authors.lastname: Wieghardt
keywords: gallium; iron; manganese; phenoxyl radicals; scandium; spectroelectrochemistry