HIGH-SPIN-]LOW-SPIN RELAXATION IN [FE(BPP)(2)](CF3SO3)(2)CENTER-DOT-H2O AFTER LIESST AND THERMAL SPIN-STATE TRAPPING - DYNAMICS OF SPIN TRANSITION VERSUS DYNAMICS OF PHASE-TRANSITION
T. Buchen et al., HIGH-SPIN-]LOW-SPIN RELAXATION IN [FE(BPP)(2)](CF3SO3)(2)CENTER-DOT-H2O AFTER LIESST AND THERMAL SPIN-STATE TRAPPING - DYNAMICS OF SPIN TRANSITION VERSUS DYNAMICS OF PHASE-TRANSITION, Chemistry, 2(9), 1996, pp. 1134-1138
The iron(II) complex [Fe(bpp)(2)]-(CF3SO3)(2) . H2O (bpp = 2,6-bis(pyr
azolyl-3-yl)pyridine) shows a thermal spin transition associated with
a hysteresis of approximately 140 K width. The transition temperatures
T-1/2 (where the fraction of HS species gamma(HS) = 0.5) are 147 K an
d approximate to 285 K in the cooling and heating directions, respecti
vely, The compound shows the LIESST and reverse-LIESST effects at low
temperatures. The relaxation of the metastable HS states generated by
LIESST was observed quantitatively at temperatures between 77.5 and 85
K by Mossbauer spectroscopy. Metastable HS states can also be generat
ed by rapid cooling of the sample. The relaxation of the metastable HS
states formed by thermal spin-state trapping was monitored at tempera
tures between 104 and 118 K by magnetic susceptibility measurements. T
he relaxation mechanisms of the HS states generated by LIESST and ther
mal spin-state trapping are completely different. We suggest that the
HS --> LS relaxation after thermal spin-state trapping is triggered by
an additional structural phase transition of the system.