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

Laurence J. Kershaw Cook, Helena J. Shepherd, Tim P. Comyn, Chérif Baldé, Oscar Cespedes, Guillaume Chastanet, Malcolm A. Halcrow

Research output: Contribution to journalArticlepeer-review

35 Citations (SciVal)


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; lowtemperature 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 lightinduced 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.

Original languageEnglish
Pages (from-to)4805-4816
Number of pages12
JournalChemistry - A European Journal
Issue number12
Early online date30 Jan 2015
Publication statusPublished - 16 Mar 2015


  • Crystal engineering
  • Iron
  • N-ligands
  • Photomagnetic properties
  • Spin crossover


Dive into the research topics of 'Decoupled spin crossover and structural phase transition in a molecular iron(II) complex'. Together they form a unique fingerprint.

Cite this