Abstract
Spin state switching on external stimuli is a phenomenon with wide applicability, ranging from molecular electronics to gas activation in nanoporous frameworks. Here, we model the spin crossover as a function of the hydrostatic pressure in octahedrally coordinated transition metal centers by applying a field of effective nuclear forces that compress the molecule towards its centroid. For spin crossover in first‐row transition metals coordinated by hydrogen, nitrogen, and carbon monoxide, we find the pressure required for spin transition to be a function of the ligand position in the spectrochemical sequence. While pressures on the order of 1 GPa are required to flip spins in homogeneously ligated octahedral sites, we demonstrate a fivefold decrease in spin transition pressure for the archetypal strong field ligand carbon monoxide in octahedrally coordinated Fe2+ in [Fe(II)(NH3)5CO]2+.
Highlights
The smallest building block of spin crossover systems is often an octahedrally coordinated transition metal center with its 3d orbitals split by the ligand field environment
Using effective nuclear forces scaled by their distances from the molecular centroid we here model spin crossover in octahedral metal-ligand complexes as a function of hydrostatic pressure
We find the pressure required for spin transition to be a function of ligand position in the spectrochemical sequence[10] and demonstrate that the spin transition pressure can be tuned by an adequate choice of the ligand field
Summary
The smallest building block of spin crossover systems is often an octahedrally coordinated transition metal center with its 3d orbitals split by the ligand field environment. Spin-flip at high pressures can be attributed to the increase in splitting of the 3d levels at the metal site such that the potential energy required to maintain a high spin configuration surpasses the spin pairing energy.[9] Using effective nuclear forces scaled by their distances from the molecular centroid we here model spin crossover in octahedral metal-ligand complexes as a function of hydrostatic pressure.
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