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Phenoxyl radical complexes of chromium(III), manganese(III), cobalt(III), and nickel(II)
Citation key ISI:000084949800033
Author Muller, J and Kikuchi, A and Bill, E and Weyhermuller, T and Hildebrandt, P and Ould-Moussa, L and Wieghardt, K
Pages 265-277
Year 2000
ISSN 0020-1693
Journal Inorganica Chimica Acta
Volume 297
Number 1-2
Month JAN
Abstract The tetradentate monoanionic macrocycles 1,4-dimethyl-7-(3-tert-butyl-5-methoxy-2-hydroxybenzyl)-1,4,7-triazacycl ononane, H(L-1), and 1,4-di-iso-propyl-7-(3,5-di-tert-butyl-2-hydroxybenzyl)-1,4,7-triazacycl ononane, H(L-2), form 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 trivalent metal ions: [M-III(L-1)(Ph(2)acac)](ClO4) M = Co-III (1), Cr-III (3), Mn-III (7), Ga-III (11); [M-II(L-t)(Ph(2)acac)] M = Ni-II (9); [M-III(L-2)(Bu(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 electrochemically, reversibly one-electron oxidized yielding stable phenoxyl radical complexes in solution. Electronic, resonance Raman and EPR spectra prove that the phenoxyl ligand is coordinated to the corresponding metal ion. The electronic ground states of complexes containing a paramagnetic transition metal ion with d(n) electron configuration and a bound phenoxyl radical (S = 1/2) are attained via an intramolecular anti- or ferromagnetic exchange coupling mechanism the nature of which depends on the actual d(n) configuration of the central metal ion: a half-filled t(2g) subshell allows antiferromagnetic coupling, for example [3](.2 +), [4](.2 +), [5](.2 +) and [6](.+) have an S-t = 1 ground state. In contrast, unpaired electrons in an e, subshell 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) 2000 Elsevier Science S.A. All rights reserved.
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