Soft X-ray Absorption Spectroscopy Study of Spin Crossover Fe-Compounds: Persistent High Spin Configurations under Soft X-ray Irradiation

• Main Authors: Ahmed Yousef Mohamed, Minji Lee, Kosuke Kitase, Takafumi Kitazawa, Jae-Young Kim, Deok-Yong Cho
• Format: Article
• Language: English
• Published: MDPI AG 2018-11-01
• Series: Crystals
• Subjects: spin crossover; X-ray absorption spectroscopy; soft X-ray induced excited spin state trapping; high spin
• Online Access: https://www.mdpi.com/2073-4352/8/11/433

Metal-organic complex exhibiting spin crossover (SCO) behavior has drawn attention for its functionality as a nanoscale spin switch. The spin states in the metal ions can be tuned by external stimuli such as temperature or light. This article demonstrates a soft X-ray⁻induced excited spin state trapping (SOXEISST) effect in Hofmann-like SCO coordination polymers of Fe^II(4-methylpyrimidine)₂[Au(CN)₂]₂ and Fe^II(pyridine)₂[Ni(CN)₄]. A soft X-ray absorption spectroscopy (XAS) study on these polymers showed that the high spin configuration (HS; S = 2) was prevalent in Fe²⁺ ions during the measurement even at temperatures much lower than the critical temperatures (>170 K), manifesting HS trapping due to the X-ray irradiation. This is in strong contrast to the normal SCO behavior observed in Fe^II(1,10-phenanthroline)₂(NCS)₂, implying that the structure of the ligand chains in the polymers with relatively loose Fe-N coordination might allow a structural adaptation to stabilize the metastable HS state under the soft X-ray irradiation.