Photomagnetism of a sym‐cis‐Dithiocyanato Iron(II) Complex with a Tetradentate N,N′‐Bis(2‐pyridylmethyl)1,2‐ethanediamine Ligand

Abstract

A comprehensive study of the magnetic and photomagnetic behaviors of cis-[Fe(picen)(NCS)(2) ] (picen = N,N'-bis(2-pyridylmethyl)1,2-ethanediamine) was carried out. The spin-equilibration was extremely slow in the vicinity of the thermal spin-transition. When the cooling speed was slower than 0.1 K min(-1), this complex was characterized by an abrupt thermal spin-transition at about 70 K. Measurement of the kinetics in the range 60-70 K was performed to approach the quasi-static hysteresis loop. At low temperatures, the metastable HS state was quenched by a rapid freezing process and the critical T(TIESST) temperature, which was associated with the thermally induced excited spin-state-trapping (TIESST) effect, was measured. At 10 K, this complex also exhibited the well-known light-induced excited spin-state-trapping (LIESST) effect and the T(LIESST) temperature was determined. The kinetics of the metastable HS states, which were generated from the freezing effect and from the light-induced excitation, was studied. Single-crystal X-ray diffraction as a function of speed-cooling and light conditions at 30 K revealed the mechanism of the spin-crossover in this complex as well as some direct relationships between its structural properties and its spin state. This spin-crossover (SCO) material represents a fascinating example in which the metastability of the HS state is in close vicinity to the thermal spin-transition region. Moreover, it is a beautiful example of a complex in which the metastable HS states can be generated, and then compared, either by the freezing effect or by the LIESST effect.

A critical review of the T(LIESST) temperature in spin crossover materials − What it is and what it is not

“…This overlap results in unusual shapes of the thermal hysteresis due to the kinetic effects, as shown in Figure 4. It also completes the magnetic and photomagnetic studies performed on cis-[Fe(picen)(NCS) 2 ] (picen= N,N'-bis(2-pyridylmethyl)1,2-ethanediamine) [47], which also belongs to the same class, with an extremely slow spin equilibration in the vicinity of the thermal spin transition. Several examples in the literature could be also regarded in the light of overlapping SCO regions, such as the 2D coordination network [Fe(bbtr) 3 ](ClO 4 ) 2 doped with Zn(II) [48].…”

Structural Dynamics of Spin Crossover in Iron(II) Complexes with Extended-Tripod Ligands

“…Thermal equilibration can be sometimes "frozen out" at cryogenic temperatures [8][9][10][11][12], so that minority states can be enriched as meta-stable species through irradiation with light or via rapid freezing. The former effect was coined as light-induced excited spin-state trapping, LIESST, whereas thermal induced excited spin-state trapping, TIESST, has been established as an alternative method for kinetic stabilization via rapid freezing [9]. Around ambient temperature, however, the exchange reactions are very rapid, leading to randomizing spin states within a few nanoseconds in most iron(II) complexes [13][14][15][16][17][18][19][20][21][22][23][24].…”

In situlaser irradiation setup for a Bruker three-circle goniometer

“…Such studies provide ample information about photochemical processes in the solid state, be it about light-induced chemical transformations (Chaudhary et al, 2017), structures of exited states (Raithby, 2015;Hatcher & Raithby, 2013) or spin-crossover phase transitions (Lé tard et al, 2012). To the best of our knowledge in the vast majority of such studies, especially those related to timeresolved crystallography, synchrotron sources were used (Fullagar et al, 2000).…”

“…One of the first such devices was designed more than a decade ago at Durham University (Thompson et al, 2004) and was successfully used for a number of years [some results are reported by Lé tard et al (2012)]. The setup consisted of a laser and a set of mirrors mounted on the 2 arm of a Bruker three-circle diffractometer equipped with a Helix (Oxford Cryosystems) cryostat.…”