Peculiar Magnetic Features and Superconductivity in Sulfur Doped Amorphous Carbon

Cu(I)/Cu(II) Creutz-Taube Mixed-Valence 2D Coordination Polymers

Graphene-like 2D coordination polymers (GCPs) have been of central research interest in recent decades with significant impact in many fields. According to classical coordination chemistry, Cu(II) can adopt the dsp² hybridization to form square planar coordination geometry, but not Cu(I); this is why so far, there has been few 2D layered structures synthesized from Cu(I) precursors. Herein a pair of isostructural GCPs synthesized by the coordination of benzenehexathiol (BHT) ligands with Cu(I) and Cu(II) ions, respectively, is reported. Spectroscopic characterizations indicate that Cu(I) and Cu(II) coexist with a near 1:1 ratio in both GCPs but remain indistinguishable with a fractional oxidation state of +1.5 on average, making these two GCPs a unique pair of Creutz-Taube mixed-valence 2D structures. Based on density functional theory calculations, an intramolecular pseudo-redox mechanism is further uncovered whereby the radicals on BHT ligands can oxidize Cu(I) or reduce Cu(II) ions upon coordination, thus producing isostructures with distinct electron configurations. For the first time, it is demonstrated that using Cu(I) or Cu(II), one can achieve 2D isostructures, indicating an unusual fact that a neutral periodic structure can host a different number of total electrons as ground states, which may open a new chapter for 2D materials.

Embedding atomic cobalt into graphene lattices to activate room-temperature ferromagnetism

Graphene is extremely promising for next-generation spintronics applications; however, realizing graphene-based room-temperature magnets remains a great challenge. Here, we demonstrate that robust room-temperature ferromagnetism with T_C up to ∼400 K and saturation magnetization of 0.11 emu g⁻¹ (300 K) can be achieved in graphene by embedding isolated Co atoms with the aid of coordinated N atoms. Extensive structural characterizations show that square-planar Co-N₄ moieties were formed in the graphene lattices, where atomically dispersed Co atoms provide local magnetic moments. Detailed electronic structure calculations reveal that the hybridization between the d electrons of Co atoms and delocalized p_z electrons of N/C atoms enhances the conduction-electron mediated long-range magnetic coupling. This work provides an effective means to induce room-temperature ferromagnetism in graphene and may open possibilities for developing graphene-based spintronics devices.

Graphene has shown incredible promise as ideal material for numerous fields; however its use in spintronics has been hampered by the lack of intrinsic magnetism. Here, Hu et al succeed in embedding Cobalt in the graphene lattice, creating robust room-temperature ferromagnetism.