科研之友
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摘要
The system [FeL2](BF4)(2) (1)-EtOH-H2O (L is 4-(3,5-dimethyl-1H-pyrazol-1-yl)-2-(pyridin-2-yl)-6-methylpyrimidine) shows a complicated balance between the relative stabilities of solvatomorphs and polymorphs of the complex [FeL2](BF4)(2). New solvatomorphs, 1(LS)center dot EtOH center dot H2O and beta-1(LS)center dot xH(2)O, were isolated in this system. They were converted into four daughter phases, 1(A/LS), 1(D/LS), 1(E/LS)center dot yEtOH center dot zH(2)O and 1(F/LS). On thermal cycling in sealed ampoules, the phases 1(LS)center dot EtOH center dot H2O and beta-1(LS)center dot xH(2)O transform into the anhydrous phase 1(A/LS). The hysteresis loop width for the 1(A/LS) <-> 1(A/HS) spin transition depends on the water and ethanol contents in the ampoule and varies from ca. 30 K up to 145 K. The reproducible hysteresis loop of 145 K is the widest ever reported one for a spin crossover complex. The phase 1(A/LS) combines the outstanding spin crossover properties with thermal robustness allowing for multiple cycling in sealed ampoules without degradation. The kinetics of the 1(A/LS) -> 1(A/HS) transition is sigmoidal which is indicative of strong cooperative interactions. The cooperativity of the 1(A/LS) -> 1(A/HS) transition is related to the formation of a 2D supramolecular structure of the phase 1(A/LS). The activation energy for the spin transition is very high (hundreds of kJ mol(-1)). The kinetics of the 1(A/HS) -> 1(A/LS) transition can either be sigmoidal or exponential depending on the water and ethanol contents in the ampoule. The phases 1(D/LS) and 1(F/LS) show gradual crossover, whereas the phase 1(E/LS)center dot yEtOH center dot yH(2)O shows a reversible hysteretic transition associated with the solvent molecule release and uptake.
- 出版日期2016
