| Summary: | 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<sup>II</sup>(4-methylpyrimidine)<sub>2</sub>[Au(CN)<sub>2</sub>]<sub>2</sub> and Fe<sup>II</sup>(pyridine)<sub>2</sub>[Ni(CN)<sub>4</sub>]. A soft X-ray absorption spectroscopy (XAS) study on these polymers showed that the high spin configuration (HS; S = 2) was prevalent in Fe<sup>2+</sup> 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<sup>II</sup>(1,10-phenanthroline)<sub>2</sub>(NCS)<sub>2</sub>, 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.
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