journal article·2025-05-20

A Mixed-Valence and Mixed-Spin Two-Dimensional Ferromagnetic Metal–Organic Coordination Framework

Xiaobo Wang, Chia-Hsiu Hsu, Chengkun Lyu, Feng-Chuan Chuang, Calvin Pei Yu Wong, Li Huang, Kuan Eng Johnson Goh, Pei-Nian Liu, Nian Lin

ACS Nano· Volume 19· Issue 19
Publisher page

Abstract

Spin-mixed systems with distinct magnetic sublattices present rich physical behaviors and hold promise for magnetic memory, thermomagnetic recording, and optoelectronics. However, most experimental studies remain confined to molecular magnetic salts rather than monolayer two-dimensional (2D) systems. Here, we report the synthesis and characterization of a 2D metal–organic framework (MOF) of Fe 2 (Fe-DPyP) 3, constructed from 5,15-di(4-pyridyl)-10,20-diphenylporphyrin (DPyP) molecules and iron atoms on a Au(111) substrate. Through scanning tunneling microscopy and density functional theory (DFT) calculations, we reveal dual coordination modes: (1) peripheral iron atoms (Fe c ) coordinate with the pyridyl substituents, forming a honeycomb lattice, and (2) central iron atoms (Fe m ) bind within the porphyrin core, creating a kagome lattice. Scanning tunneling spectroscopy highlights distinct spin-flip excitations in the bivalent Fe m atoms with a magnetic spin state of S = 1, while the monovalent Fe c atoms display a V-shaped dip around the Fermi level, attributed to the quenched spin excitations or a soft Coulomb gap, with a magnetic spin state of S = 3/2. DFT calculations reveal an in-plane ferromagnetic ground state with spin-polarized Fe d orbitals and molecular p orbitals. This work contributes to the understanding of mixed-valence and mixed-spin 2D coordination networks with implications for the development of next-generation quantum materials and spintronic devices.
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Research context

OpenAlex topics: Metal-Organic Frameworks: Synthesis and Applications · Magnetism in coordination complexes · Metal complexes synthesis and properties

SciVX discovery tags are terminology-based. OpenAlex topics are source-provided classifications.

Affiliations

Industries Training Centre

Shenzhen Polytechnic University

Department of Physics

The Hong Kong University of Science and Technology

National Sun Yat-sen University

Physics Division

National Center for Theoretical Sciences

Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Singapore

Department of Physics, State Key Laboratory of Quantum Functional Materials, and Guangdong Basic Research Center of Excellence for Quantum Science

Southern University of Science and Technology

Quantum Science Center of Guangdong-Hong Kong-Macao Greater Bay Area (Guangdong)

Quantum Innovation Centre (Q.InC), Agency for Science, Technology and Research (A*STAR), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Singapore

Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551, Singapore

Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore

Shanghai Key Laboratory of Functional Materials Chemistry and School of Chemistry & Molecular Engineering, East China University of Science and Technology, Meilong Road 130, Shanghai 200237, China

Funding

Research Grants Council, University Grants Committee · Agency for Science, Technology and Research · National Key Research and Development Program of China · National Research Foundation Singapore · National Natural Science Foundation of China · Ministry of Science and Technology, Taiwan

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