Unexpected Spin-Crossover and a Low-Pressure Phase Change in an Iron(II)/Dipyrazolylpyridine Complex Exhibiting a High-Spin Jahn- Teller Distortion.
Inorg Chem
; 54(13): 6319-30, 2015 Jul 06.
Article
em En
| MEDLINE
| ID: mdl-26351707
ABSTRACT
The synthesis of 4-methyl-2,6-di(pyrazol-1-yl)pyridine (L) and four salts of [FeL2]X2 (X = BF(4)(), 1; X = ClO(4)(), 2; X = PF(6)(), 3; X = CF3SO(3)(), 4) are reported. Powder samples of 1 and 2 both exhibit abrupt, hysteretic spin-state transitions on cooling, with T(1/2)↓ = 204 and T(1/2)↑ = 209 K (1), and T(1/2)↓ = 175 and T(1/2)↑ = 193 K (2). The 18 K thermal hysteresis loop for 2 is unusually wide for a complex of this type. Single crystal structures of 2 show it to exhibit a JahnTeller-distorted six-coordinate geometry in its high-spin state, which would normally inhibit spin-crossover. Bulk samples of 1 and 2 are isostructural by X-ray powder diffraction, and undergo a crystallographic phase change during their spin-transitions. At temperatures below T(1/2), exposing both compounds to 10(5) Torr pressure inside the powder diffractometer causes a reversible transformation back to the high-temperature crystal phase. Consideration of thermodynamic data implies this cannot be accompanied by a low â high spin-state change, however. Both compounds also exhibit the LIESST effect, with 2 exhibiting an unusually high T(LIESST) of 112 K. The salts 3 and 4 are respectively high-spin and low-spin between 3 and 300 K, with crystalline 3 exhibiting a more pronounced version of the same JahnTeller distortion.
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MEDLINE
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En
Ano de publicação:
2015
Tipo de documento:
Article