Study on the spin-crossover transition in [Fe( cis-/ trans-stpy) 4(X) 2] (stpy: styrylpyridine, X: NCS, NCBH 3) under high pressure toward ligand-driven light-induced spin change

Abstract

Toward the realization of a ligand-driven light-induced spin change (LD-LISC) around room temperature, we have investigated the spin-crossover phenomenon in [Fe(stpy) 4(X) 2] (stpy = styrylpyridine, X = NCS, NCBH 3) under high pressure. The spin transition temperature increases from 110 to 220 K with increasing applied pressure up to 0.75 GPa for [Fe( trans-stpy) 4(NCS) 2], while [Fe( cis-stpy) 4(NCS) 2] shows the high-spin state in the temperature region between 2 and 300 K even at 0.75 GPa. In the case of X = NCBH 3, due to the stronger ligand field of NCBH 3, the spin transition temperature increases from 240 to 360 K with increasing applied pressure up to 0.50 GPa for [Fe( trans-stpy) 4(NCBH 3) 2]. In the case of [Fe( cis-stpy) 4(NCBH 3) 2], the spin state is the high-spin state in the temperature region between 2 and 300 K. However, the spin transition appears at 125 K under 0.5 GPa and the transition temperature increases with increasing applied pressure. In this way, we have decided the applied pressure region of 0.65–1.09 GPa where [Fe(stpy) 4(NCBH 3) 2] undergoes LD-LISC at room temperature.