Compensation effects and relation between the activation energy of spin transition and the hysteresis loop width for an iron(II) complex

Compensation effects and relation between the activation energy of spin transition and the hysteresis loop width for an iron(II) complex Full article

Journal

Physical Chemistry Chemical Physics
ISSN: 1463-9076 , E-ISSN: 1463-9084

Output data

Year: 2016, Volume: 18, Number: 25, Pages: 16690-16699 Pages count : 10 DOI: 10.1039/c6cp01892k

Authors

Bushuev Mark B. ^1,2 , Pishchur Denis P. ¹ , Nikolaenkova Elena B. ³ , Krivopalov Viktor P. ³

Affiliations

1	(Данные Web of science) Russian Acad Sci, Siberian Branch, Nikolaev Inst Inorgan Chem, 3 Acad Lavrentiev Ave, Novosibirsk 630090, Russia
2	(Данные Web of science) Novosibirsk State Univ, 2 Pirogova Str, Novosibirsk 630090, Russia
3	(Данные Web of science) Russian Acad Sci, Siberian Branch, NN Vorozhtsov Novosibirsk Inst Organ Chem, 9 Acad Lavrentiev Ave, Novosibirsk 630090, Russia

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.

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 OpenAlex

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

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Web of science	10
Scopus	11
Elibrary	11
OpenAlex	12