The ligand field in low-crystallinity metal–organic frameworks investigated by soft X-ray core-level absorption spectroscopy

The ligand field (LF) of transition metal ions is a crucial factor in realizing the mechanism of novel physical and chemical properties. However, the low-crystallinity state, including the amorphous state, precludes the clarification of the electronic structural relationship of transition metal ions...

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Bibliographic Details
Published in:Physical chemistry chemical physics : PCCP 2022-07, Vol.24 (27), p.16680-16686
Main Authors: Yamagami, Kohei, Yoshino, Haruka, Yamagishi, Hirona, Setoyama, Hiroyuki, Tanaka, Arata, Ohtani, Ryo, Ohba, Masaaki, Wadati, Hiroki
Format: Article
Language:English
Subjects:
Absorption spectroscopy
Charge transfer
Chemical properties
Crystal structure
Crystallinity
Crystallography
Electric fields
Electron states
Intermetallic compounds
Iron
Ligands
Magnetic measurement
Manganese
Metal ions
Metal-organic frameworks
Nickel
Nitrogen
Optics
Palladium
Soft x rays
Spectrum analysis
Transition metals
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Summary:The ligand field (LF) of transition metal ions is a crucial factor in realizing the mechanism of novel physical and chemical properties. However, the low-crystallinity state, including the amorphous state, precludes the clarification of the electronic structural relationship of transition metal ions using crystallographic techniques, ultraviolet and infrared optical methods, and magnetometry. Here, we demonstrate that soft X-ray 2p → 3d core-level absorption spectroscopy ( L 2,3 -edge XAS) systematically revealed the local 3d electronic states, including in the LF, of nitrogen-coordinated transition-metal ions for low-crystallinity cyanide-bridged metal–organic frameworks (MOFs) M [Ni(CN) 4 ] (MNi; M = Mn, Fe, Co, Ni) and Ni[Pd(CN) 4 ] (NiPd). In NiNi and NiPd, N-coordinated Ni ions with square-planar symmetry exhibit strong orbital hybridization and ligand-to-metal charge transfer effects. In MnNi, FeNi, and CoNi, the correlation between the crystalline electric field splitting in the LF and the transition metal–nitrogen bonding length is revealed using the multiplet LF theory. Regardless of the different local symmetries, our results indicate that L 2,3 -edge XAS is a powerful tool for gaining element-specific knowledge about the transition–metal ion characterizing the functionality of low-crystallinity MOFs and will be the foundation for an attractive platform, such as adsorption/desorption materials.
ISSN:1463-9076
1463-9084
DOI:10.1039/d2cp01415g