Re-investigation of the spin crossover phenomenon in the ferrous complex [Fe(HB(pz)3)2]

Abstract

The temperature dependence of the magnetic susceptibility, optical reflectivity and electrical conductivity of [Fe(HB(pz) 3 ) 2 ] (pz = pyrazolyl) revealed irreversible changes in the material during the low-spin to high-spin transition when the ''as-prepared'' sample was heated above B400 K for the first time. During this first heating sequence, the initially fine powder sample became coarse, and its crystal structure changed from tetragonal to monoclinic. Single-crystals of the monoclinic form suitable for X-ray analysis could be isolated after the first thermal cycle, and their structure was resolved in the P2 1 /n (Z = 4) space group. Successive cooling and heating cycles did not lead to further modification of the crystal structure, and the temperature dependence of the physical properties remained invariable. Remarkably, the electrical conductivity of the sample measured at 293 K dropped from 6.1 Â 10 À8 to 2.1 Â 10 À11 S m À1 following the first thermal cycle-suggesting possible applications of this material in read-only memory devices (ROM).

The disentangling of hysteretic spin transition, polymorphism and metastability in bistable thin films formed by sublimation of bis(scorpionate) Fe(ii) molecules

“…These differences may result from a polymorphic modification and a texture effect. 20,36 After the film annealing (one hour at 100 °C), the new patterns ( Fig. 2 and S11) evidence the irreversible transformation of a metastable state.…”

Spin-State Tuning at Pseudo-tetrahedral d6 Ions: Spin Crossover in [BP3]FeII–X Complexes

“…This would likely result in decreased crystallinity or more defect-ridden crystals with a higher concentration of grain boundaries, which would be expected to lead to a more gradual and incomplete spin transition, as is observed. 3 If the sample is heated to 400 K under vacuum for several hours prior to measurement in the SQUID magnetometer, this change is no longer observed and the initial heating and cooling curves are identical ( Figure S46). Table S11.…”

Charge Transport and Electrical Properties of Spin Crossover Materials: Towards Nanoelectronic and Spintronic Devices

“…The first report on the conductivity switching of a bulk SCO solid was published in 2009 [36]. In this work, Salmon et al re-investigated the spin crossover phenomenon in the [Fe(HB(pz) 3 ) 2 ] (pz = pyrazolyl) complex by magnetic, calorimetric, optical, crystallographic and electrical means.…”