Decoupled spin crossover and structural phase transition in a molecular iron(II) complex.
Chemistry
; 21(12): 4805-16, 2015 Mar 16.
Article
em En
| MEDLINE
| ID: mdl-25641549
ABSTRACT
Crystalline [Fe(bppSMe)2][BF4]2 (1; bppSMe = 4-(methylsulfanyl)-2,6-di(pyrazol-1-yl)pyridine) undergoes an abrupt spin-crossover (SCO) event at 265±5â
K. The crystals also undergo a separate phase transition near 205â
K, involving a contraction of the unit-cell a axis to one-third of its original value (high-temperature phaseâ
1; Pbcn, Z = 12; low-temperature phaseâ
2; Pbcn, Z = 4). The SCO-active phaseâ
1 contains two unique molecular environments, one of which appears to undergo SCO more gradually than the other. In contrast, powder samples of 1 retain phaseâ
1 between 140-300â
K, although their SCO behaviour is essentially identical to the single crystals. The compounds [Fe(bppBr)2][BF4]2 (2; bppBr = 4-bromo-2,6-di(pyrazol-1-yl)pyridine) and [Fe(bppI)2][BF4]2 (3; bppI = 4-iodo-2,6-di(pyrazol-1-yl)-pyridine) exhibit more gradual SCO near room temperature, and adopt phaseâ
2 in both spin states. Comparison of 1-3 reveals that the more cooperative spin transition in 1, and its separate crystallographic phase transition, can both be attributed to an intermolecular steric interaction involving the methylsulfanyl substituents. All three compounds exhibit the light-induced excited-spin-state trapping (LIESST) effect with T(LIESST = 70-80â
K), but show complicated LIESST relaxation kinetics involving both weakly cooperative (exponential) and strongly cooperative (sigmoidal) components.
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MEDLINE
Idioma:
En
Ano de publicação:
2015
Tipo de documento:
Article