Реферат: The enthalpy-entropy compensation was observed for the cooperative 1(A/LS) -> 1(A/HS) spin transition (the phase 1(A) is a mononuclear complex [FeL2](BF4)(2), L is 4-(3,5-dimethyl-1H-pyrazol-1-yl)-2-(pyridin-2-yl)-6- methylpyrimidine). The physical origin of this effect is the fact that the 1(A/LS) -> 1(A/HS) spin transition is the first order phase transition accompanied by noticeable variations in the T-onset up arrow, Delta H and Delta S values. Higher Delta H and Delta S values are correlated with higher T-onset up arrow values. The higher the enthalpy and entropy of the spin transition, the wider the hysteresis loop. The kinetic compensation effect, i.e. a linear relationship between lnA and E-a, was observed for the 1(A/LS) -> 1(A/HS) spin transition. Moreover, an isokinetic relationship was detected in this system: the Arrhenius lines (ln k vs. 1/T) obtained from magnetochemical data for different samples of the phase 1(A) undergoing the 1(A/LS) -> 1(A/HS) transition show a common point of intersection (T-iso = 490 +/- 2 K, ln k(iso) = -6.0 +/- 0.2). The validity of this conclusion was confirmed by the Exner-Linert statistical method. This means that the isokinetic relationship and the kinetic compensation effect (ln A vs. E-a) in this system are true ones. The existence of a true kinetic compensation effect is supported independently by the fact that the hysteresis loop width for the cooperative spin transition 1(A/LS) <-> 1(A/HS) increases with increasing activation barrier height. Estimating the energy of excitations for the phase 1(A/LS) with T-iso similar to 490 K yields wavenumbers of ca. 340 cm(-1) corresponding to the frequencies of the stretching vibrations of the Fe-LS-N bonds, i.e. the bonds directly involved in the mechanism of the spin transition. This is the first observation of the kinetic compensation effect (ln A vs. E-a) and the isokinetic relationship for a cooperative spin crossover system showing thermal hysteresis. Our results provide the first experimental evidence that the higher the activation barrier for the spin transition, the wider the hysteresis loop for a series of related spin crossover systems.

Библиографическая ссылка: Bushuev M.B. , Pishchur D.P. , Nikolaenkova E.B. , Krivopalov V.P.
Compensation effects and relation between the activation energy of spin transition and the hysteresis loop width for an iron(II) complex
Physical Chemistry Chemical Physics. 2016. V.18. N25. P.16690-16699. DOI: 10.1039/c6cp01892k WOS Scopus РИНЦ

Идентификаторы:

Web of science	WOS:000378711100009
Scopus	2-s2.0-84976332510
РИНЦ	27140839
OpenAlex	W2408041194

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