Intermolecular interactions of tetrabenzoporphyrin- and phthalocyanine-based charge-transfer complexes

Diamond lattice in single-component molecular crystals comprising tetrabenzoporphyrin neutral radicals

A single-component molecular radical crystal of CoIII(tbp˙-)(CN)2, where tbp = tetrabenzoporphyrinato ligand, exhibiting a diamond lattice was fabricated as a potential candidate for a three-dimensional Dirac electron system. Band structure calculations revealed that the Fermi energy level was located at the Dirac point. A small electrical resistivity of 160 Ω cm was observed at 2 K under the application of 2.4 GPa. Furthermore, substituting CoIII by FeIII or MnIII led to the introduction of local magnetic moments into the diamond-lattice system. MIII(tbp˙-)L2 crystals will open up uncharted fields in the study of the Dirac electron systems.

Dioxygen Activation and Reduction by a Soluble Iron Phthalocyanine

Iron ions in a square-planar coordination can bind molecules at the vacant axial positions and are able to transform them in stoichiometric and catalytic reactions. Nature takes advantage of these properties by incorporating iron into porphyrin systems, which play a key role not only in the binding and transport of oxygen, but also in catalytic oxidation and reduction reactions involving cytochrome P450. Although these systems have been studied extensively, there are still unresolved questions regarding the interplay between the iron ions and the surrounding ligands. Phthalocyanines (Pc) create a similar environment for metal atoms and FePc is known for a long time. However, without axial ligands FePc aggregates leading to solids of low solubility. In this work we used a known six-coordinate iron phthalocyanine derivative with bulky substituents and removed the stabilizing axial ligands. The resulting paramagnetic, four-coordinate compound does not aggregate and dissolves well so that NMR spectroscopy can be employed for studying the molecular structure and the reactivity. Solvent molecules bind weakly to the iron centers and oxygen is reduced in the presence of H-atom donors. The stoichiometric and catalytic reactivity with oxygen was studied in more detail.

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 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 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 π-d interaction is present in the [Fe^III(1,2-Nc)(CN)₂] unit. Although the magnetic interaction between π-conduction electrons and Fe^III-d spins (π-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.