High-Pressure EPR Study of Spin Molecular Bistability in Li[Fe(Th-5Cl-Sa)_2]

The spin transitions in Li[Fe(Th-5Cl-Sa)2] were studied by EPR under hydrostatic pressure in the temperature range 80 332 K. The structural changes in the complex anion induced by the pressure above 350 MPa (when LS-2 phase appears) are observed, which are manifested in abrupt changes in g⊥ factor and linewidth ∆B⊥ of the low-spin phase LS. It is also manifested in the change in the shape of EPR spectrum. The high-spin ↔ low-spin transition HS ↔ LS shows hysteresis whose width is constant up to about 265 K and then rapidly increases. The spin phase diagram studied shows a large similarity to the phase diagram of (2Me-5Et-PyH)[Fe(Th-5Cl-Sa)2], which means that characteristics of the transition depend mainly on complex anion, not on cation. The hysteresis indicates on a cooperative character of the spin transition and on grouping of the complexes in domains.