ISSN:
0947-6539
Keywords:
gallium
;
iron
;
scandium
;
spectroelectrochemistry
;
manganese
;
phenoxyl radicals
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The hexadentate macrocyclic ligands 1,4,7-tris(3,5-dimethyl-2-hydroxybenzyl)-1,4,7-triazacyclononane (LCH3H3), 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 (LOCH3-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′); [LOCH3M], where M = Ga (1 a), Sc (2 a), Fe (3 a); [LOCH3MnIV]PF6 (4 a'); [LCH3M], where M = Sc (2 b), Fe (3 b), MnIII (4 b); [LCH3MnIV]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 [LOCH3FeIII]ClO4 and [LOCH3GaIII]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 [MnIVLOCH3]2+ is accessible.
Additional Material:
17 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/chem.19970030221
