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

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)2·6H2O, 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(CAn)CoIII(TPyA)]z+ [z = 3, n = 3− (13+); 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 [CoIICA2-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 13+ 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 2n+ 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·S2 for 12+ and 22+; H = −2J(S1·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-.