Structural Bifurcation in the High→Low-Spin and Low→High-Spin Phase Transitions Explains the Asymmetric Spin-Crossover in [FeL₂][BF₄]₂ (L=2,6-Di{pyrazol-1-yl}isonicotinonitrile).

ABSTRACT: Polycrystalline [FeL₂][BF₄]₂ (L=2,6-di(pyrazol-1-yl)isonicotinonitrile) exhibits an abrupt hysteretic spin transition near 240 K, with a shoulder on the warming branch whose appearance depends on the sample history. The freshly isolated material is a ca 60 : 40 mixture of triclinic (HS1) and tetragonal (HS2) high-spin polymorphs, which are structurally closely related. Both HS1 and HS2 undergo a high→low-spin transition on cooling at 230±10 K. HS1 transforms to a new triclinic low-spin phase with a doubled unit cell volume (LS3), while HS2 forms a monoclinic low-spin phase (LS4) with similar unit cell dimensions to HS2. Single crystals of LS3 and LS4 both convert to HS1 on rewarming. The low→high-spin transition for LS4 is ca 10 K higher in temperature than

SUBMITTER: Ahmed A 

PROVIDER: S-EPMC11773316 | biostudies-literature | 2025 Jan

REPOSITORIES: biostudies-literature