An electrically conducting molecular crystal composed of a magnetic iron(iii) complex (S = 1/2) with a large aromatic ligand, 1,2-naphthlalocyanine (C 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, PhP[Fe(1,2-Nc)(CN)] (PhP = tetraphenylphosphonium and 1,2-Nc = C isomer of 1,2-naphthalocyanine), was fabricated as a new coordination compound with a strong π-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 PhP[Fe(1,2-Nc)(CN)] was isostructural to its non-magnetic analogue PhP[Co(1,2-Nc)(CN)] but possessed higher electrical resistivity, indicating that the strong intramolecular π-d interaction is present in the [Fe(1,2-Nc)(CN)] unit. Although the magnetic interaction between π-conduction electrons and Fe-d spins (π-d interaction) is crucial for the emergence of a negative magnetoresistance effect, the negative magnetoresistance effect of PhP[Fe(1,2-Nc)(CN)] was significantly smaller (-6% at 30 K under a static 9 T magnetic field) than those of PhP[Fe(Pc)(CN)] (-32%) and PhP[Fe(tbp)(CN)] (-13%) analogues (Pc = phthalocyanine and tbp = tetrabenzoporphyrin). This small negative magnetoresistance effect of PhP[Fe(Pc)(CN)] 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.