KERSHAW COOK, Laurence J.; SHEPHERD, Helena; COMYN, Tim P.; BALDÉ, Chérif; CESPEDES, Oscar; CHASTANET, Guillaume; HALCROW, Malcolm A

doi:10.1002/chem.201406307

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KERSHAW COOK, Laurence J.
School of Chemistry [Leeds]

SHEPHERD, Helena
Department of Chemistry

COMYN, Tim P.
Institute for Materials Research

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Chemistry - A European Journal. 2015, vol. 21, n° 12, p. 4805-4816

Wiley-VCH Verlag

Résumé en anglais

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±5 K. The crystals also undergo a separate phase transition near 205 K, involving a contraction of the unit-cell a axis to one-third of its original value (high-temperature phase 1; Pbcn, Z=12; low-temperature phase 2; Pbcn, Z=4). The SCO-active phase 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 phase 1 between 140-300 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 phase 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=70-80 K), but show complicated LIESST relaxation kinetics involving both weakly cooperative (exponential) and strongly cooperative (sigmoidal) components.< Réduire

Mots clés en anglais

crystal engineering

iron

N‐ligands

photomagnetic properties

spin crossover

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Decoupled spin crossover and structural phase transition in a molecular iron(II) complex

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