Spin Crossover in the {Fe(pz)[Pt(CN)<sub>4</sub>]} Metal–Organic
Framework upon Pyrazine Adsorption
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Abstract
The
spin-crossover behavior of the {Fe(pz)[Pt(CN)<sub>4</sub>]} metal–organic
framework (MOF) upon pyrazine adsorption is investigated through hybrid
Monte Carlo/molecular dynamics (MC/MD) simulations. In contrast to
previous theoretical studies, which reported a transition temperature
of ∼140 K, the present MC/MD simulations predict that the high-spin
state is the most stable state at all temperatures, in agreement with
the experimental observations. The MC/MD simulations also indicate
that the pyrazine molecules adsorbed in the MOF pores lie nearly parallel
but staggered by 60° relative to the pyrazine ligands of the
framework. The analysis of the magnetization curve as a function of
the temperature demonstrates that the staggered configuration assumed
by the guest pyrazine molecules within the framework is responsible
for the stabilization of the high-spin state. Both the guest pyrazine
molecules and the pyrazine ligands of the framework are effectively
locked into the minimum-energy configuration and do not display any
rotational mobility