Pressure-induced hysteresis in the high spin low spin transition in bis(2,4-bis(pyridin-2-yl)thiazole) iron(II) tetrafluoroborate

Abstract

Studies of the spin transition behavior of the mononuclear compound[Fe(pythiaz)2](BF4)2 have been carried out under hydrostatic pressures up to 9.13 kbar in the 5–300 Ktemperature range. Under ambient pressure this compound exhibits an approximatelyhalf-step (incomplete) HS LS transition with T1/2 = 146 K without any thermal hysteresis. At pressures up to 4.5 kbarthe behavior remains similar but with an upward displacement ofT1/2 and a slight decrease in the residual high spin fraction at lowT. Application of higher pressures resulted in an almost complete two-step spin transitionwith several unusual pressure effects. Along with the expected pressure dependence ofT1/2 the surprising appearance of hysteresis in the spin transition curves was observed. It issuggested that the likely origin of this unprecedented behavior is a pressure-inducedstructural change.