Ashis Bhattacharjee*, Masataka Tsugimoto, Yashuhiro Nakazawa* and Harold A. Goodwin Pages 65 - 72 ( 8 )
Background: [Fe(bpp)2](NCS)2.2H2O exhibits a two-step spin transition between the 5T2 state (HS, S = 2) and the 1A1 state (LS, S = 0) below room temperature, both steps being associated with thermal hysteresis. The present study explored the nature of spin transition (ST) in [Fe(bpp)2](NCS)2.2H2O under pressure to determine if ST could be induced to go to completion and whether a two-step process was then involved.Methods: Magnetic measurements were performed on polycrystalline samples of [Fe(bpp)2] (NCS)2.2H2O in the temperature range of 100 - 300 K under different applied pressures up to 0.5 GPa. Results: [Fe(II)(bpp)2](NCS)2.2H2O under ambient pressure exhibited a two-step HS LS transition with two thermal hysteresis loops while the second loop appears at γHS = 0.25. As the applied pressure increased from ambient, γHS decreased, the high temperature thermal hysteresis gradually diminished while the low temperature thermal hysteresis shifted to higher temperatures and vanished at 0.5 GPa applied pressure. The γHS values estimated at 300 K during cooling and heating protocols followed an exponential decay equation. Conclusion: [Fe(bpp)2](NCS)2.2H2O at room temperature may have four high spin Fe(II) ions out of which three are having nearly identical coordination environment, while the remaining rests in a very rigid environment. Application of 0.5 GPa pressure on the compound below 250 K converts all the HS states to LS state. Temperature dependent structural and Mössbauer spectroscopic studies may identify the proposed crystallographically independent Fe(II) HS sites in [Fe(bpp)2](NCS)2.2H2O at higher temperatures, and hence unearth the anomalous spin transition exhibited by this compound.
Spin transition, Fe(II), high pressure, magnetization, pressure effect studies, spin crossover.
Department of Physics, Institute of Science, Visva-Bharati University, Santiniketan-731235, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560 0043, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, School of Chemical Sciences, University of New South Wales, UNSW 2052