Molecular Mechanisms of Spin Crossover in the {Fe(pz)[Pt(CN)₄]} Metal–Organic Framework upon Water Adsorption

Abstract

The rational design of multifunctional materials with properties that can be selectively controlled at the molecular level is key to the development and application of nanoscale devices. In this study, molecular dynamics simulations using ligand-field molecular mechanics are performed to elucidate, for the first time, the molecular mechanisms responsible for the variation of the spin-crossover properties of the {Fe(pz)[Pt(CN)4]} metal-organic framework upon water adsorption. The simulations demonstrate a direct relationship between the water loading adsorbed in the pores and the variation of the spin-crossover transition temperature, with the high-spin state of the material becoming gradually more stabilized as the number of adsorbed water molecules increases. The decrease of the spin-crossover temperature of {Fe(pz)[Pt(CN)4]} upon water adsorption predicted by the simulations is in agreement with the available experimental data and is traced back to the elongation of the bonds between the Fe(II) atoms and the organic linkers induced by interactions of the adsorbed water molecules with the framework.

Molecular Spin Crossover Materials: Review of the Lattice Dynamical Properties

“…In another example, neutron‐scattering experiments performed on the compound {Fe(pyrazine)[Pt(CN) 4 ]} revealed that ≈10% of the total entropy change (85 J K −1 mol −1 ) arises from the rotational entropy contribution of the pyrazine ligands . This finding was also corroborated by MD simulations ΔS el corresponds to the electronic entropy variation and has contributions from orbital and spin degeneracies.…”

“…Molecular dynamics deals with atomic positions and velocities determined by the interatomic force fields, which enable then the calculation of vibrational spectra. MD simulations on SCO compounds were performed only recently . For example, a simple model system, consisting of coordination octahedra, was investigated using both periodic boundary conditions (bulk material) and open boundary conditions (nanoparticles) .…”

“…It was shown that LFMM‐based calculations can provide as accurate results as DFT for SCO compounds—at a substantially reduced computational cost . Notably, this advantage of LFMM was exploited in hybrid Monte Carlo/MD simulations with periodic boundary conditions to analyze the SCO properties of {Fe(pyrazine)[Pt(CN) 4 ]} porous coordination network solids in relation with the dynamical properties of both the host network and adsorbed guest molecules …”

A Ligand Field Molecular Mechanics Study of CO2‐Induced Breathing in the Metal–Organic Framework DUT‐8(Ni)

“…Structural characteristics of the MOF explain the shape of the energy profile at different loading states and provide useful insights to the interpretation of previous experimental results.the possibilities of employing ligand field molecular mechanics (LFMM) simulations to study flexible MOFs and their processes. The method employed is not limited to adsorption processes but as has been shown previously [8][9][10][11] to be applicable to other properties, for example, spin states or magnetic properties. Our goal is to present simulations using the example of CO 2induced breathing in the pillared layer MOF DUT-8(Ni) [12] (Ni 2 (ndc) 2 (dabco), ndc = 2,6naphthalenedicarboxylate, dabco = 1,4diazabicyclo-[2.2.2]-octane, see Figure 1) using an LFMM approach.…”

Cooperativity of Spin Crossover Complexes: Combining Periodic Density Functional Calculations and Monte Carlo Simulation

“…The right one instead—which may well be lower in energy and lead to a smaller $\mathrm{normal\Gamma }\left(c\right)$—can only be assessed if the calculations are performed for large systems that are out of reach for DFT methods. Recently, hybrid Monte Carlo/molecular dynamics (MC/MD) calculations with ligand field force fields (LF FF) have been presented to overcome this problem [14,15,16]. An alternative approach using Ising-like models is presented in the next section.…”