An electrically conducting molecular crystal composed of a magnetic iron(iii) complex (S=1/2) with a large aromatic ligand, 1,2-naphthlalocyanine (C4h isomer): towards the development of molecular spintronics

The field of molecular spintronics has gained significant attention for the development of second-generation spintronic devices. Therefore, an electrically conducting molecular crystal, Ph4P[Fe-III(1,2-Nc)(CN)(2)](2) (Ph4P = tetraphenylphosphonium and 1,2-Nc = C-4h isomer of 1,2-naphthalocyanine), was fabricated as a new coordination compound with a strong pi-d interaction. Furthermore, it is a mixed-valence compound with a local spin of S = 1/2 at the center of the conduction path. Crystal structure analysis revealed that Ph4P[Fe-III(1,2-Nc)(CN)(2)](2) was isostructural to its non-magnetic analogue Ph4P[Co-III(1,2-Nc)(CN)(2)](2) but possessed higher electrical resistivity, indicating that the strong intramolecular pi-d interaction is present in the [Fe-III(1,2-Nc)(CN)(2)] unit. Although the magnetic interaction between pi-conduction electrons and Fe-III-d spins (pi-d interaction) is crucial for the emergence of a negative magnetoresistance effect, the negative magnetoresistance effect of Ph4P[Fe-III(1,2-Nc)(CN)(2)](2) was significantly smaller (-6% at 30 K under a static 9 T magnetic field) than those of Ph4P[Fe-III(Pc)(CN)(2)](2) (-32%) and Ph4P[Fe-III(tbp)(CN)(2)](2) (-13%) analogues (Pc = phthalocyanine and tbp = tetrabenzoporphyrin). This small negative magnetoresistance effect of Ph4P[Fe-III(Pc)(CN)(2)](2) could be ascribed to the weak intermolecular antiferromagnetic interaction between its d spins. Hence, this study showed that constructing a molecular design for strengthening the intermolecular antiferromagnetic interaction is key to enhancing the negative magnetoresistance effect.

Automated summary

A new electrically conducting molecular crystal with strong pi-d interaction was fabricated and studied for its negative magnetoresistance effect. It was found that enhancing the intermolecular antiferromagnetic interaction in molecular design is crucial for improving the negative magnetoresistance effect.