Investigation of the High-Temperature Spin-Transition of a Mononuclear Iron(II) Complex Using X-ray Photoelectron Spectroscopy

Abstract

This study presents a new mononuclear complex (1) of the form [FeL](BF), incorporating the thiazolylimine donor moiety, which was found to exhibit a high-temperature spin-transition. The effect of scan rate was investigated, with magnetic susceptibility being measured at 4, 2, and 1 K min. The magnetic susceptibility results were confirmed by variable temperature X-ray photoelectron spectroscopy (XPS) (100, 270, 400, and 500 K) and single crystal X-ray diffraction (150 and 400 K) experiments. A rare example of a high-temperature (400 K) single crystal structure of 1 has been reported. The high-spin fraction was calculated indirectly from XPS data, presenting a method for analyzing the spin-state in the surface layers of spin-crossover materials.

Iron(II) Spin Crossover Complex with the 1,2,3-Triazole-Containing Linear Pentadentate Schiff-Base Ligand and the MeCN Monodentate Ligand

“…For the real-world applications, SCO compounds must fulfill demands such as a proper room temperature (RT) response, abrupt spin transition, wide thermal hysteresis, and high durability at least [6,7]. Multistep [8][9][10][11] and high-temperature (HT) [12][13][14][15][16][17][18] SCO complexes also provide demands for the development of multinary memories and for the investigation of the thermal stability of spin transition under extreme conditions, respectively. These properties are complicatedly affected by the ligand field strength of each SCO molecule and cooperativity between SCO metal sites.…”

Probing the unpaired Fe spins across the spin crossover of a coordination polymer

“…The results from magnetic susceptibility measurements for [Fe(L1)(bipy)] n given as  M T versus temperature plot (black), and the occupancy of the high spin state derived from empirical X-ray absorption (XAS) spectra (red curve), with increasing temperature. The Fe 2p 3/2 core level photoemission feature widths, measured here in X-ray photoemission, are far broader than seen for other dielectric Fe 2+ iron based materials, 27,41,42,44,58,59 but of similar half width to some of the spin crossover molecular systems measured by photoemission. 43,45,59 In fact, what is observed with increasing temperature is a significant intrinsic broadening of the Fe 2p 3/2 core level photoemission feature, with increasing temperature.…”

“…As seen for many transition metals, this large intrinsic Fe 2p 3/2 core level line width is a very good indicator that there are multiplets. 27,[41][42][43][44][45][58][59][62][63][64] The increase of the width in the principal Fe 2p 3/2 core level photoemission feature, as plotted in Figure 4, is indicative of a decrease of the photoemission lifetime with increasing temperature.…”

“…This system exhibits a wide thermal hysteresis in the spin transition, above room temperature. 18 While X-ray absorption spectroscopy (XAS) is frequently used to probe changes in electronic structure, 17,[25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] X-ray core level photoemission at the Fe 2p core has also been used to probe the molecular spin crossover, 27,[41][42][43][44][45] but only in a limited manner. So far, data from X-ray photoemission spectroscopy (XPS) has not been adequate to make a detailed comparison with magnetometry or XAS, nor has the XPS data been sufficient to abstract a critical spin crossover transition temperature.…”

“…One is the light induced activation of the low spin to high spin state switch, i.e. light-induced excited spin-state trapping (LIESST), 4,26,[40][41][42][43][44][45][46][47][48][49][50][51][52][53][54] and soft X-ray-induced excited spin state trapping (SOXIESST). 26 These light and X-ray induced spin state changes occur at temperatures well below the spin crossover temperature (T 1/2 ) where the low spin state should be dominant.…”