Anilino radical complexes of cobalt(III) and manganese(IV) and comparison with their phenoxyl analogues

The pendent arm macrocyclic aniline ligands 1-(2-amino-3,5-di-tert-butylbenzyl)-4,7-dimethyl-1,4,7-triazacyclononane, H[L-1], and 1,4,7-tris(2-amino-3,5-di-tert-butylbenzyl)-1,4,7-triazacyclononane, H-3[L-2], have been synthesized. The reaction of these ligands in methanol (1:1) and/or ethanol with Co-II(ClO4)(2). 6H(2)O and potassium di-tert-butylacetylacetonate (1:1) or Mn-II(acetate)(2). 4H(2)O in the presence of air produced the anilide complexes [Co-III(L-1)(Bu(2)acac)](ClO4) (1) and [Mn-IV(L-2)]X (X = ClO4 (2), BPh4 (2')), respectively. The reaction of H-3[L-2] and CuCl2. 2H(2)O in ethanol produced upon addition of NaClO4 blue crystals of [Cu-II(H3L2)Cl](ClO4) (3) containing two coordinated and one uncoordinated aniline pendent arm. Complexes 1, 2, and 3 have been structurally characterized by X-ray crystallography. Electrochemically, 1 is reversibly oxidized with formation of the paramagnetic anilino radical species [Co-III(L-1 .)(Bu(2)acac)(2+) (S = 1/2) whereas the cyclic voltammogram of 2 displays three ligand-centered one-electron-transfer oxidation waves where complexes [Mn-IV(L-2 .)](2+), [Mn-IV(L-2 . .)](3+), and [Mn-IV(L-2 . . .)](4+) containing one, two, and three coordinated anilino radicals are formed successively. These anilino radical species have been characterized by UV-vis, X-band EPR, and resonance Raman spectroscopy. The characteristic spectroscopic features of coordinated anilino radicals have been elucidated. In the Mn-IV radical species strong intramolecular exchange coupling between the metal ion (t(2)g(3) configuration, S = 3/2) and one, two, or three anilino radicals (S-rad = 1/2) produces the ground states S, = 1, S-t = 1/2, and S-t = 0 in the di-, tri-, and tetracation of the parent complex 2, respectively.