Despite the fact that Fe(pyrazine)[MII (CN)4] (where MII is a metal in open square-planar configuration, namely Pt, Pd, Ni) is one of the most thoroughly studied families of spin-crossover compounds, its actual structure has remained imprecisely known up to now. Using neutron diffraction and density-functional theory calculations, we demonstrate that the pyrazine rings, instead of being disordered in two orthogonal positions in the low-spin phase, adopt an ordered arrangement with the rings alternatively oriented in these two positions. This finding has a direct implication on the most characteristic property of these systems, the spin-crossover transition, which is notably affected by this arrangement. This is because the energy difference between both spin states depends on the pyrazine configuration and the ordering of the rings changes the balance of entropy contributions to the entropy-driven spin-crossover phenomenon.

The development of strategies to efficiently capture and release gas is one of the most urgent topics in modern applied chemistry. In this respect, the modulation of the affinity for the gas molecule upon application of an external stimulus appears as fascinating strategy to reduce the energy penalty of the release process. In this work we provide the proof- of-concept for a novel temperature-induced gas release strategy in porous materials with desorption occurring upon a spin crossover transition of metal center exhibiting an open coordination. By employing a recently proposed Hubbard-U density- corrected scheme within density-functional theory we demonstrate the feasibility of the proposed process from a thermodynamic point of view by correlating the change in binding energy of several gas molecules upon spin crossover with the adiabatic energy difference associated with the spin state change for a series of six porous coordination polymers. The case of H2 ad- sorption stands out as the most promising and yet novel result with implications for a non-cryogenic storage technology.

The development of strategies to efficiently capture and release gas is one of the most studied topics in modern applied chemistry. In this respect, the modulation of the affinity for the gas molecule upon application of an external stimulus appears as fascinating strategy to reduce the energy penalty of the release process. In this work we provide the proof-of-concept for a novel temperature-induced gas release strategy in porous materials with desorption occurring upon a spin crossover transition of metal center exhibiting an open coordination. By employing a recently proposed Hubbard-U density-corrected scheme within density-functional theory we demonstrate the feasibility of the proposed process from a thermody- namic point of view by correlating the change in binding energy of several gas molecules upon spin crossover with the adiabatic energy difference associated with the spin state change for a series of six porous coordination polymers. The case of H2 adsorption stands out as the most promising and yet novel result with implications for a non-cryogenic storage technology.