Mechanochemical Effect in the Iron(III) Spin Crossover Complex [Fe(3-MeO-salenEt)2]PF6 as Studied by Heat Capacity Calorimetry
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- 作者：Michio Sorai ; Ramó ; n Burriel ; Edgar F. Westrum ; Jr. ; David N. Hendrickson
- 刊名：Journal of Physical Chemistry B
- 出版年：2008
- 出版时间：April 10, 2008
- 年：2008
- 卷：112
- 期：14
- 页码：4344 - 4350
- 全文大小：180K
- 年卷期：v.112,no.14(April 10, 2008)
- ISSN：1520-5207
文摘
Magnetic and thermal properties of the iron(III) spin crossover complex [Fe(3MeO-salenEt)2]PF6 are verysensitive to mechanochemical perturbations. Heat capacities for unperturbed and differently perturbed sampleswere precisely determined by adiabatic calorimetry at temperatures in the 10-300 K range. The unperturbedcompound shows a cooperative spin crossover transition at 162.31 K, presenting a hysteresis of 2.8 K. Theanomalous enthalpy and entropy contents of the transition were evaluated to be 
fchars/Delta.gif" BORDER=0 >trsH = 5.94 kJ mol-1 andfchars/Delta.gif" BORDER=0 >trsS = 36.7 J K-1 mol-1, respectively. By mechanochemical treatments, (1) the phase transition temperaturewas lowered by 1.14 K, (2) the enthalpy and entropy gains at the phase transition due to the spin crossoverphenomenon were diminished to fchars/Delta.gif" BORDER=0 >trsH = 4.94 kJ mol-1 and fchars/Delta.gif" BORDER=0 >trsS = 31.1 J K-1 mol-1, and (3) the lattice heatcapacities were larger than those of the unperturbed sample over the whole temperature range. In spite ofdifferent mechanical perturbations (grinding with a mortar and pestle and grinding in a ball-mill), two sets ofheat capacity measurements provided basically the same results. The mechanochemical perturbation exertsits effect more strongly on the low-spin state than on the high-spin state. It shows a substantial increase ofthe number of iron(III) ions in the high-spin state below the transition temperature. The heat capacities of thediamagnetic cobalt(III) analogue [Co(3MeO-salenEt)2]PF6 also were measured. The lattice heat capacity ofthe iron compounds has been estimated from either the measurements on the cobalt complex using acorresponding states law or the effective frequency distribution method. These estimations have been usedfor the evaluation of the transition anomaly.
fchars/Delta.gif" BORDER=0 >trsH = 5.94 kJ mol-1 andfchars/Delta.gif" BORDER=0 >trsS = 36.7 J K-1 mol-1, respectively. By mechanochemical treatments, (1) the phase transition temperaturewas lowered by 1.14 K, (2) the enthalpy and entropy gains at the phase transition due to the spin crossoverphenomenon were diminished to fchars/Delta.gif" BORDER=0 >trsH = 4.94 kJ mol-1 and fchars/Delta.gif" BORDER=0 >trsS = 31.1 J K-1 mol-1, and (3) the lattice heatcapacities were larger than those of the unperturbed sample over the whole temperature range. In spite ofdifferent mechanical perturbations (grinding with a mortar and pestle and grinding in a ball-mill), two sets ofheat capacity measurements provided basically the same results. The mechanochemical perturbation exertsits effect more strongly on the low-spin state than on the high-spin state. It shows a substantial increase ofthe number of iron(III) ions in the high-spin state below the transition temperature. The heat capacities of thediamagnetic cobalt(III) analogue [Co(3MeO-salenEt)2]PF6 also were measured. The lattice heat capacity ofthe iron compounds has been estimated from either the measurements on the cobalt complex using acorresponding states law or the effective frequency distribution method. These estimations have been usedfor the evaluation of the transition anomaly.