Thermal trapped iron(II) high spin state investigated by X-ray diffraction

Abstract

The possibilities to trap by flash cooling the high spin (HS) state of iron(II) in the [Fe(PM -BiA) 2 (NCS) 2 ] complex have been investigated by X-ray diffraction. This study reveals that trapping the HS state is possible under some conditions depending on the final temperature. If the latter is lower than the T(LIESST) temperature, the HS ! LS (low spin) relaxation is slow enough to determine the trapped HS crystal structure by X-ray diffraction. The crystal structure of this complex in the 30 K trapped HS state shows differences from either the room temperature (HS) or the 30 K (LS) crystal structures, as for example differences in the strength of the S· · ·H -C hydrogen bond like intermolecular interaction or the p-p interactions, known to play a crucial role in this compound for the propagation of the change in spin at the spin crossover (SCO), i.e. the cooperativity. The differences in intermolecular interactions are directly linked to the differences between the crystallographic unit cell modifications induced by pure thermal effects and those induced by the SCO. q

Intermolecular control of thermoswitching and photoswitching phenomena in two spin-crossover polymorphs

“…45 This is in agreement with the conclusions previously drawn from the comparison between the thermally quenched HS state at 30 K and the room-temperature HS state in BIA I. 52 Such similarities might be due to the absence of symmetry breaking during the first-order phase transition. The thermal hysteresis of BIA I is associated with growing of long-range domains of HS and LS phases, as demonstrated here by the coexistence of the corresponding Bragg peaks [see Fig.…”

Photoinduced phenomena and structural analysis associated with the spin-state switching in the[FeII(DPEA)(NCSGlijer1, Hebert2, Trzop3 et al. 2008Phys. Rev. B17250View full textAdd to dashboardCite

“…4 and 6). Such a situation has already been observed in other spin crossover systems, either mononuclear 34,35 or binuclear ones 36 .…”

Effects of Internal and External Pressure on the [Fe(PM-PEA)2(NCS)2] Spin-Crossover Compound (with PM-PEA = N-(2′-pyridylmethylene)-4-(phenylethynyl)aniline)

“…This observation contrasts with the TIESST effect whose efficiency increases from 1 (8%) to 3 (30%) but remains at this level upon further metal dilution. This is probably due to the experiment that is only a fast cooling from 300 K to 10 K and not an instant quench, which strongly differs from the thermal-quenching previously performed on an X-Ray diffractometer, showing similar structures between the high temperature and the metastable HS phases [55]. Note that the discrepancy between magnetic and diffraction experiments in term of quenching effect investigation were discussed elsewhere on a similar material [56].…”