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

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: Fe(phen)(2)(NCS)(2), [Fe(3-Fpy)(2){Ni(CN)(4)}], and [Fe(3-Fpy)(2){Pt(CN)(4)}]. The changes in the Fe 2p core-level spectra with temperature indicate spin state transitions in these SCO complexes, which are consistent with one's expectations and the existing literature. Additionally, the temperature dependence of the binding energy of the N 1s core-level provides further physical insights into the ligand-to-metal charge transfer phenomenon in these molecules. The high-spin fraction versus temperature plots reveal that the surface of each of the molecules studied herein is found to be in the high-spin state at temperatures both in the vicinity of room temperature and below their respective transition temperature alike, with the stability of the high-spin state of these molecules varying with the choice of ligand.