Study on the spin-crossover transition in [Fe(cis-/trans-stpy)4(X)2] (stpy: styrylpyridine, X: NCS, NCBH3) under high pressure toward ligand-driven light-induced spin change

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, NCBH3) 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 = NCBH3, due to the stronger ligand field of NCBH3, the spin transition temperature increases from 240 to 360 K with increasing applied pressure up to 0.50 GPa for [Fe(trans-stpy)(4)(NCBH3)(2)]. In the case of [Fe(cis-stpy)(4)(NCBH3)(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)(NCBH3)(2)] undergoes LD-LISC at room temperature. (C) 2011 Elsevier Ltd. All rights reserved.