Metal-organic frameworks (MOFs) represent an interesting class of versatile materials with important properties, including magnetism. However, the synthesis of atomically precise large-scale 2D MOFs with nontrivial strong magnetic coupling represents a current research challenge. In this regard, we report on the synthesis of a high-quality large-scale 2D MOF, with strong π-d magnetic exchange coupling. To this aim, we present a new two-step synthetic approach that consists of the initial formation of an extended supramolecular organic framework on a Au(111) surface, establishing the large-scale order of organic ligands and their subsequent metalation by single cobalt atoms assisted by annealing. Moreover, we show that the usage of radical asymmetric organic ligands enables us to form a magnetic 2D MOF with strong π-d electron interactions. According to the multireference calculations, the 2D MOF shows complex spin interactions beyond the traditional superexchange mechanism, with the interplay between antiferromagnetic and ferromagnetic couplings. We anticipate that this synthetic strategy can be adapted to different approaches, such as liquid interfaces or insulating substrates, to synthesize high-quality 2D MOFs. Accompanied by the high control with atomic precision over the magnetic properties of the ligands and metals, this approach enables the formation of large-scale 2D MOFs with complex spin interactions, which will open new avenues in the field of 2D magnetic materials.

• Publication type
• Journal Article MeSH

Open-shell nanographenes exhibit unconventional π-magnetism arising from topological frustration or strong electron-electron interaction. However, conventional design approaches are typically limited to a single magnetic origin, which can restrict the number of correlated spins or the type of magnetic ordering in open-shell nanographenes. Here we present a design strategy that combines topological frustration and electron-electron interactions to fabricate a large fully fused 'butterfly'-shaped tetraradical nanographene on Au(111). We employ bond-resolved scanning tunnelling microscopy and spin-excitation spectroscopy to resolve the molecular backbone and reveal the strongly correlated open-shell character, respectively. This nanographene contains four unpaired electrons with both ferromagnetic and anti-ferromagnetic interactions, harbouring a many-body singlet ground state and strong multi-spin entanglement, which is well described by many-body calculations. Furthermore, we study the magnetic properties and spin states in the nanographene using a nickelocene magnetic probe. The ability to imprint and characterize many-body strongly correlated spins in polyradical nanographenes paves the way for future advancements in quantum information technologies.

• Publication type
• Journal Article MeSH

Precise control of multiple spin states on the atomic scale presents a promising avenue for designing and realizing magnetic switches. Despite substantial progress in recent decades, the challenge of achieving control over multiconfigurational reversible switches in low-dimensional nanostructures persists. Our work demonstrates multiple, fully reversible plasmon-driven spin-crossover switches in a single π-d metal-organic chain suspended between two electrodes. The plasmonic nanocavity stimulated by external visible light allows for reversible spin crossover between low- and high-spin states of different cobalt centers within the chain. We show that the distinct spin configurations remain stable for minutes under cryogenic conditions and can be nonperturbatively detected by conductance measurements. This multiconfigurational plasmon-driven spin-crossover demonstration extends the available toolset for designing optoelectrical molecular devices based on SCO compounds.

• Keywords
• density functional theory, light-induced switching, molecular chains, one-dimensional system, scanning tunneling microscopy, spin crossover, transport,
• Publication type
• Journal Article MeSH

Submolecular charge distribution significantly affects the physical-chemical properties of molecules and their mutual interaction. One example is the presence of a π-electron-deficient cavity in halogen-substituted polyaromatic hydrocarbon compounds, the so-called π-holes, the existence of which was predicted theoretically, but the direct experimental observation is still missing. Here we present the resolution of the π-hole on a single molecule using the Kelvin probe force microscopy, which supports the theoretical prediction of its existence. In addition, experimental measurements supported by theoretical calculations show the importance of π-holes in the process of adsorption of molecules on solid-state surfaces. This study expands our understanding of the π-hole systems and, at the same time, opens up possibilities for studying the influence of submolecular charge distribution on the chemical properties of molecules and their mutual interaction.

• Publication type
• Journal Article MeSH