Phenoxyl radical complexes of chromium(III), manganese(III), cobalt(III), and nickel(II)

The tetradentate monoanionic macrocycles 1,4-dimethyl-7-(3-tert-butyl-5-met hoxy-2-hydroxybenzyl)-1,4,7-triazacyclononane, H(L-1), and 1,4-di-iso-propy l-7-(3,5-di-tert-butyl-2-hydroxybenzyl)-1,4,7-triazacyclononane, H(L-2), fo rm in the presence of a bidentate coligand 1,3-diphenyl-1,3-propanedionate, Ph(2)acac, 1,3-dimethyl-1,3-propanedionate, acac, or 1,3-di-tert-butyl-1,3 -dionate, Bu(2)acac(-), very stable octahedral complexes with di- or trival ent metal ions: [M-III(L-1)(Ph(2)acac)](ClO4) M = Co-III (1), Cr-III (3), M n-III (7), Ga-III (11); [M-II(L-t)(Ph(2)acac)] M = Ni-II (9); [M-III(L-2)(B u(2)acac)](ClO4) M = Co-III (2), Cr-III (4), Mn-III (8), Ga-III (12), [M-II (L-1)(Bu(2)acac)] M = Ni-II (10); [Cr-III(L-2)(acac)](ClO4) (5), [Cr-III(L- 2)(C2O4)] (6). All of these monophenolatometal complexes can be electrochem ically, reversibly one-electron oxidized yielding stable phenoxyl radical c omplexes in solution. Electronic, resonance Raman and EPR spectra prove tha t the phenoxyl ligand is coordinated to the corresponding metal ion. The el ectronic ground states of complexes containing a paramagnetic transition me tal ion with d(n) electron configuration and a bound phenoxyl radical (S = 1/2) are attained via an intramolecular anti- or ferromagnetic exchange cou pling mechanism the nature of which depends on the actual d(n) configuratio n of the central metal ion: a half-filled t(2g) subshell allows antiferroma gnetic coupling, for example [3](.2 +), [4](.2 +), [5](.2 +) and [6](.+) ha ve an S-t = 1 ground state. In contrast, unpaired electrons in an e, subshe ll enforce a ferromagnetic coupling. [9](.2) (+), [10](.2 +) have an S-t = 3/2 ground state. The crystal structures of 1, 5, and 9 are reported. (C) 2 000 Elsevier Science S.A. All rights reserved.