Deposition of the Spin Crossover Fe^II–Pyrazolylborate Complex on Au(111) Surface at the Molecular Level

Abstract

The interaction at the molecular level of the spin‐crossover (SCO) FeII((3,5‐(CH3)2Pz)3BH)2 complex with the Au(111) surface is analyzed by means of rPBE periodic calculations. Our results show that the adsorption on the metallic surface enhances the transition energy, increasing the relative stability of the low spin (LS) state. The interaction indeed is spin‐dependent, stronger for the low spin than the high spin (HS) state. The different strength of the Fe ligand field at low and high temperature manifests on the nature, spatial extension and relative energy of the states close to the Fermi level, with a larger metal–ligand hybridization in the LS state. This feature is of relevance for the differential adsorption of the LS and HS molecules, the spin‐dependent conductance, and for the differences found in the corresponding STM images, correctly reproduced from the density of states provided by the rPBE calculations. It is expected that this spin dependence will be a general feature of the SCO molecule–substrate interaction, since it is rooted in the different ligand field of Fe site at low and high temperatures, a common hallmark of the FeII SCO complexes. Finally, the states involved in the LIESST phenomenon has been identified through NEVPT2 calculations on a model reaction path. A tentative pathway for the photoinduced LS→HS transition is proposed, that does not involve the intermediate triplet states, and nicely reproduces both the blue laser wavelength required for the activation, and the wavelength of the reverse HS → LS transition.

Spin-state-dependent electrical conductivity in single-walled carbon nanotubes encapsulating spin-crossover molecules

“…At the same time, the interaction (adsorption) with the nanotube is stronger for the LS than the HS state in all the explored geometries (Table 1). Similar results have been obtained for the [Fe((3,5-(CH 3 ) 2 Pz) 3 BH) 2 ] complex deposited on the Au(111) surface 42 as well as for [Fe(phen) 2 (NCS) 2 ] on metallic substrates 43,44 . This behavior can be rationalized on the basis of the orbital mixing between the molecule and the nanotube, stronger for the LS state, as shown by the projected density of states in Fig.…”

Spin-crossover complexes in nanoscale devices: main ingredients of the molecule–substrate interactions

“…This is not a particular feature of the molecule-SWCNT interaction, but it has been also observed for the deposition of Fe (II) SCO complexes on different substrates. 35,36,40,53 These results are in line with the opening of a hysteresis observed in our I vs. T measurements 42 as well as many others measurements in the literature. 65,66 The differential stabilization of the LS state of the confined molecule is driven by the Fe ligand field, which is higher for the LS than the HS state.…”

“…[49][50][51][52] rPBE functional has been proven to provide a good LS-HS balance (much better than other GGA functionals such as PBE) for well-known SCO complexes containing Fe(II) and Fe(III), 25 and has been previously employed to describe the deposition of SCO complexes on different substrates. 36,37,53 Valence electrons are described using a plane-wave basis set with a cutoff of 500 eV and the Γpoint of the Brillouin zone is used. 54 The optimized lattice parameters for the nanotube are a = b = 16.75 Å and c = 11.35 Å.…”

“…The same trends have been reported for the deposition of similar Fe SCO complexes on metallic substrates. 35,36,40,53 This can be related to the spin-dependent degree of mixing of the molecules and nanotube states. Fig.…”

“…The aim of this work is to explore in depth, with the help of state-of-the-art quantum chemistry calculations, the different aspects of the integration of SCO molecules on active nanodevices. While the relative stability of the LS and HS states of Fe(II) and Fe(III) SCO complexes have been extensively evaluated in the gas-phase, [24][25][26][27][28][29][30][31][32][33][34] works devoted to the theoretical study of SCO complexes on the surface are rather scarce, [35][36][37][38][39][40][41] even though they can provide valuable information on the molecular scale, difficult or impossible to measure, such as details of bonding on surfaces, or the impact of strong electric fields. For this study, we take benefit from a recent work where two Fe(II) SCO complexes are encapsulated within single-walled carbon nanotubes (SWCNT) (Fig.…”