On Stabilizing Spin Crossover Molecule [Fe(Tbu(2)Qsal)(2)] On Suitable Supports: Insights From Ab Initio Studies

Au(111) is one of the substrates often used for supporting spin crossover (SCO) molecules, partly because of its inertness and partly because it is conducting. Using density functional theory based calculations of [Fe(tBu(2)qsal)(2)] SCO molecules adsorbed on the Au(111) surface, we show that while Au(111) may not be a suitable support for the molecule, it may be so for a monolayer (ML) of molecules. While, physisorption of [Fe(tBu(2)qsal)(2)] on Au(111) leads to electron transfer from the highest occupied molecular orbital to the substrate, electron transfer is minimal for a ML of [Fe(tBu(2)qsal)(2)] on Au(111), causing only negligible changes in the electronic structure and magnetic moment of the molecules. Furthermore, a small difference in energy between the ferromagnetic and antiferromagnetic configurations of the molecules in the ML indicates a weak magnetic coupling between the molecules. These results suggest Au(111) as a plausible support for a ML of [Fe(tBu(2)qsal)(2)], making such a molecular assembly suitable for electronic and spin transport applications. As for [Fe(tBu(2)qsal)(2)] SCO molecules themselves, we find hexagonal boron nitride (h-BN) to be a viable support for them, as there is hardly any charge transfer, while graphene displays stronger interaction with the molecule (than h-BN does) resulting in charge transfer from the molecule to graphene.