Dinuclear Fe(II) Spin-Crossover Complex Deposited on the Au(111) Surface: Exploration Based on Quantum-Chemistry Calculations

We present the first computational study dealing with the interaction of a dinuclear Fe(II) spin-crossover complex with a metal surface. Density functional theory-based calculations have been employed to determine the electronic structure and geometry of the deposited molecules and the persistence of the spin transition. The studied dinuclear Fe(II) complex presents a two-step transition in the bulk, switching abruptly from the [LSLS] to the [LSHS] state and gradually from the mixed state to the [HSHS] state. Our results confirm the same behavior for a single molecule in the absence of packing interactions. When deposited on gold, the molecule preferentially adopts a vertical orientation, with respect to the surface. The mixed spin state [LSHS] is favored over the pure [LSLS] and [HSHS] states, with a noticeable distortion of the coordination sphere of the Fe HS center close to the metal surface. Although the separation with the [LSLS] state is small, the transition from the [LSHS] to [LSLS] state would be blocked by the negative entropy change. A second conformer, higher in energy, has also been identified, where the axial axes of the Fe coordination octahedra are parallel to the surface. In such a case, the [LSLS] solution is the ground state, and a thermal switching to the mixed [LSHS] state would be possible at a rather low temperature. In all of the conformations explored, the [HSHS] solution is too high in energy, and a complete switching to the [HSHS] state is then discarded for the deposited molecule at room temperature.