A Hofmann-type two-step spin-crossover (SCO) complex with a pyrimidine derivative ligand was synthesized.

The spin-crossover (SCO) phenomenon is an active area of research. This paper describes the synthesis of an Fe−Ag Hofmann-type complex, {Fe(4methylpyrimidine) 2 [Ag(CN) 2 ] 2 }, which demonstrates a one-step SCO and single-layer Hofmann-type structure with Ag−N interactions and no Ag−Ag interactions, which is strikingly different from the previously synthesized complex {Fe(4-methylpyrimidine) 2 [Au-(CN) 2 ] 2 } that contains Au−Au interactions and no Au−N interactions. This difference can be explained in terms of the lack of relativistic effect in the Ag atoms and the different cooperative effects caused by their different structures. A scan-rate-dependent hysteresis is observed using magnetic measurement whereas not using 57 Fe Mossbauer spectroscopy, suggesting that the spin transition is relatively slow.

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 FeII(4-methylpyrimidine)2[Au(CN)2]2 and FeII(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 FeII(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.

The crystal structure of the polymeric spin crossover compound Fe(3,4-dimethyl-pyridine)2[Ag(CN)2]2 has been solved and its temperature dependence followed by means of single-crystal and powder X-ray diffraction. This compound presents a two-step spin transition with relatively abrupt steps centred at ca. 170 K and 145 K and a plateau at around 155 K. The origin of the two-step transition is discussed in light of these structural studies. The observations are compatible with a mostly disordered state between the two steps, consisting of mixing of high-spin and low-spin species, while weak substructure reflections in the mixed phase could indicate some degree of long-range order of the high-spin and low-spin sites.

We synthesized novel “Soma–Iwamoto-type” complexes that contain the 4-methoxypyrimidine ligand. The guest clathrate complexes demonstrate the SCO phenomenon and interesting rarely reported penetrated structures with two Soma–Iwamoto-type structures.