Synthesis, structure, and magnetic properties of valence ambiguous dinuclear antiferromagnetically coupled cobalt and ferromagnetically coupled iron complexes containing the chloranilate(2-) and the significantly stronger coupling chloranilate(•3-) radical trianion

Kil Sik Min, Antonio G. DiPasquale, James A. Golen, Arnold L. Rheingold, Joel S. Miller

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Abstract

Dinuclear [(TPyA)MII(CA2-)MII(TPyA)] 2+ [TPyA = tris(2-pyridylmethyl)amine; CA2- = chloranilate dianion; M = Co (12+), Fe (22+)] complexes have been prepared by the reaction of M(BF4)2·6H 2O, TPyA, H2CA, and triethylamine in MeOH solution. Their reduced forms [(TPyA)MII(CA•3-)MII(TPyA)] + [M = Co(1+), Fe (2+)] have been synthesized by using cobaltocene, and oxidized forms of 1, [(TPyA)CoIII(CA n)-CoIII(TPyA)]z+ [z = 3, n = 3- (1 3+); z = 4, n = 2- (14+)], have been obtained by using FcBF4 and ThianBF4 (Fc = ferrocenium; Thian = thianthrinium), respectively. The dinuclear compound bridged chloranilates (CA2- or CA•3-) were isolated and characterized by X-ray crystallography, electrochemistry, magnetism, and EPR spectroscopy. Unlike the other redox products, valence ambiguous 13+ forms via a complex redox-induced valence electron rearrangement whereby the one-electron oxidation of the [CoIICA2-CoII]2+ core forms [CoIIICA•3-CoIII]3+, not the expected simple 1-e- transfer mixed-valent [CoIICA 2-CoIII]3+ core. The M ions in 1 and 2 have a distorted octahedral geometry by coordination with four nitrogens of a TPyA, two oxygens of a chloranilate. Due to the interdimer offset face-to-face π-π and/or herringbone interactions, all complexes show extended 1-D and/or 2-D supramolecular structures. The existence of CA•3- in 1 3+ is confirmed from both solid-state magnetic and solution EPR data. Co-based 1n+ exhibit antiferromagnetic interactions [12+: g = 2.24, J/kB = -0.65 K (-0.45 cm-1); 1+: g = 2.36, J/kB = -75 K (52 cm-1)], while Fe-based 2 n+ exhibit ferromagnetic interactions [22+: g = 2.08, J/kB = 1.0 K (0.70 cm-1); 2+; g = 2.03, J/kB = 28 K (19 cm-1)] [H = -2JS1·S 2 for 12+ and 22+; H = -2J(S 1·S2 + S2·S3) for 1+ and 2+]. Thus, due to direct spin exchange CA •3- is a much strong spin coupling linkage than the superexchange spin-coupling pathway provided by CA2-.

Original languageEnglish
Pages (from-to)2360-2368
Number of pages9
JournalJournal of the American Chemical Society
Volume129
Issue number8
DOIs
StatePublished - 28 Feb 2007

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