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Issue 42, 2016
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A giant negative magnetoresistance effect in an iron tetrabenzoporphyrin complex

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By measuring the electrical resistivity in TPP[FeIII(tbp)(CN)2]2 (TPP = tetraphenylphosphonium and tbp = tetrabenzoporphyrin) under the application of a static magnetic field, a giant negative magnetoresistance (MR) effect with high anisotropy is observed. More specifically, the MR ratio at 13 K under a field of 9 T perpendicular to the c axis is −70%, whereas the MR ratio under a field parallel to the c axis is −40%. Furthermore, electron spin resonance (ESR) measurements indicate large anisotropy in the principal g-values of d spin (S = 1/2) in the [FeIII(tbp)(CN)2] unit; the g1 value almost perpendicular to the tbp plane and the g2 and g3 values almost parallel to the tbp plane are 3.60, 1.24, and 0.39, respectively. It is revealed that the anisotropy in the MR effect arises from the anisotropy in the d spin, suggesting that the d spins in TPP[FeIII(tbp)(CN)2]2 affect the π-conduction electron via the intramolecular π–d interaction. The anisotropy and magnitude in the giant negative MR effect for TPP[FeIII(tbp)(CN)2]2 are smaller than the corresponding values for the isostructural phthalocyanine (Pc) analogue TPP[FeIII(Pc)(CN)2]2. This is consistent with the fact that the intermolecular antiferromagnetic d–d interaction in TPP[FeIII(tbp)(CN)2]2 (suggested by the Weiss temperature: Θ = −8.0 K) is weaker than that in TPP[FeIII(Pc)(CN)2]2 (Θ = −12.3 K). This indicates that the minor modification in coordination complexes can significantly affect the MR effect via tuning the intermolecular d–d interaction as well as the intermolecular π–π overlap.

Graphical abstract: A giant negative magnetoresistance effect in an iron tetrabenzoporphyrin complex

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The article was received on 14 May 2016, accepted on 20 Jul 2016 and first published on 21 Jul 2016

Article type: Paper
DOI: 10.1039/C6DT01911K
Citation: Dalton Trans., 2016,45, 16604-16609
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    A giant negative magnetoresistance effect in an iron tetrabenzoporphyrin complex

    M. Nishi, M. Ikeda, A. Kanda, N. Hanasaki, N. Hoshino, T. Akutagawa and M. Matsuda, Dalton Trans., 2016, 45, 16604
    DOI: 10.1039/C6DT01911K

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