10.1021/ic8020589.s001 Toshihide Mochizuki Toshihide Mochizuki Takashi Nogami Takashi Nogami Takayuki Ishida Takayuki Ishida Ferromagnetic Superexchange Coupling through a Diamagnetic Iron(II) Ion in a Mixed-Valent Iron(III, II, III) <i>meso</i>-Helicate American Chemical Society 2009 Ferromagnetic Superexchange ground state III terminal S II ion superexchange mechanism 2009-03-02 00:00:00 Dataset https://acs.figshare.com/articles/dataset/Ferromagnetic_Superexchange_Coupling_through_a_Diamagnetic_Iron_II_Ion_in_a_Mixed_Valent_Iron_III_II_III_i_meso_i_Helicate/2874961 <i>meso</i>-Helicates [Ni<sub>3</sub>(pzNTR)<sub>6</sub>]·4CH<sub>3</sub>CN and [Fe<sub>3</sub>(pzNTR)<sub>6</sub>](ClO<sub>4</sub>)<sub>2</sub>·CH<sub>3</sub>OH were prepared (HpzNTR stands for <i>N-tert</i>-butyl-α-3-pyrazolylnitrone). The former showed antiferromagnetic coupling between neighboring ions with <i>J</i>/<i>k</i><sub>B</sub> = −28.2(2) K, which can be reasonably interpreted in terms of the superexchange mechanism. On the other hand, the latter exhibited ferromagnetic coupling with <i>J</i>/<i>k</i><sub>B</sub> = +0.292(8) K between the two terminal <i>S</i> = 5/2 Fe<sup>3+</sup> ions through the intervening diamagnetic Fe<sup>2+</sup> ion. The admixture of low-lying excited states with the ground state stabilizes the ferromagnetically coupled state, like the Prussian blue magnet.