Surface stabilisation of the high-spin state of Fe(ii) spin-crossover complexes

Abstract

Temperature dependent X-ray photoemission spectroscopy (XPS) has been employed to examine the Fe 2p and N 1s core levels of the studied Fe(II) spin crossover (SCO) complexes of interest, namely:...

Is the surface of Hofmann-like spin-crossover {Fe(pz)[Pt(CN)4]} the same as its bulk?

“…Therefore, the high value of room-temperature HS occupancy especially at the surface of the {Fe(pz)[Pt(CN) 4 ]} nanocrystal, and its great immunity to thermal fluctuations, opens new pathways for room-temperature spintronics and quantum information science applications. Overall, our results elucidate that the use of XPS to study the differences between the surface and bulk magnetic character of SCO materials is not limited just to a certain kind of SCO complex, 6 but it can rather be employed to investigate the aforementioned nature of a wide range of SCO complexes.…”

“…2a and b, respectively. As described elsewhere, 6 the ligand-to-metal charge transfer (LMCT) will get weaker, due to the elongation of Fe–N bonds, as the temperature is increased; therefore, as before, 6 the HS electronic configuration is assigned in the XPS peak at the higher binding energy, whereas the LS electronic configuration is assigned in the XPS peak at the lower binding energy. This assignment of the XPS peaks is also consistent with the elevated effective nuclear charge experienced by the Fe 2p electrons in the HS configuration.…”

“…Fe-based spin crossover (SCO) complexes, with Fe in the +2 oxidation state, are materials where the Fe( ii ) atoms are surrounded by an octahedral ligand field. In these Fe( ii ) SCO complexes, even some minor external perturbations, like variations in the magnetic field 1,2 or temperature, 3–6 can lead to a detectable change in their spin state. 7–13 Owing to the temperature sensitivity of the octahedral ligand field splitting ( Δ oct ) between the t 2g and e g orbitals, these complexes tend to occupy the low-spin state (LS), exhibiting a diamagnetic character ( S = 0), at low temperatures.…”

“…Conversely, lowering the Δ oct between the t 2g and e g orbitals by increasing the temperature, beyond their respective critical transition temperature T c , makes these complexes transition to a paramagnetic high-spin state (HS) with S = 2. 12,14–18 The bistability of these spin states 7,19,20 and the facility with which these spin states can be transitioned in the Fe( ii ) SCO complexes 6 make these materials come off as great candidates for nonvolatile memory applications. 21–23 The existence of room-temperature magnetic moment in these molecules may also be exploited for room-temperature spintronics 24,25 and molecular transistor-based quantum information science applications.…”

“…1a), some popular non-invasive techniques like X-ray absorption spectroscopy and X-ray photoemission spectroscopy (XPS) have been employed to detect these transitions in the Fe( ii ) SCO complexes without the application of an external magnetic field. 6,30–41 In this work, temperature-dependent XPS has been used to monitor the evolution of the Fe 2p and N 1s core-level photoemission spectra of the nanocrystals of 3D Hoffman-like {Fe(pz)[Pt(CN) 4 ]} (schematic shown in Fig. 1b) with temperature.…”