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

Kreutzburg, Lars; Hübner, Christian G.; Paulsen, Hauke

doi:10.3390/ma10020172

Cited by 8 publications

(11 citation statements)

References 44 publications

(91 reference statements)

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“…Finally, we observed that the overall effect of the anharmonic correction was in general small enough to rely on the much simpler harmonic model, which gave direct estimates of the ZPE and ∆S without having to perform energy scans along the normal modes of the system under study. To proceed towards a computational strategy that is capable of reliably predicting transition temperatures for thermal spin crossover, it is more important to focus on a more sophisticated material model; environmental effects [64,65] and cooperativity [66,67] are expected to have a much larger influence than the anharmonic corrections.…”

Section: Discussionmentioning

confidence: 99%

The Role of Vibrational Anharmonicity in the Computational Study of Thermal Spin Crossover

Sousa

Graaf

2019

Magnetochemistry

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Spin crossover in transition metal complexes can be studied in great detail with computational chemistry. Over the years, the understanding has grown that the relative stability of high-spin (HS) versus low-spin (LS) states is a subtle balance of many factors that all need to be taken into account for a reliable description. Among the different contributions, the zero-point energy (ZPE) and the entropy play key roles. These quantities are usually calculated assuming a harmonic oscillator model for the molecular vibrations. We investigated the impact of including anharmonic corrections on the ZPE and the entropy and indirectly on the critical temperature of spin crossover. As test systems, we used a set of ten Fe(II) complexes and one Fe(III) complex, covering different coordination modes (mono-, bi-, and tri-dentate ligands), decreasing coordination number upon spin crossover, coordination by second- and third-row atoms, and changes in the oxidation state. The results show that the anharmonicity has a measurable effect, but it is in general rather small, and tendencies are not easily recognized. As a conclusion, we put forward that for high precision results, one should be aware of the anharmonic effects, but as long as computational chemistry is still struggling with other larger factors like the influence of the environment and the accurate determination of the electronic energy difference between HS and LS, the anharmonicity of the vibrational modes is a minor concern.

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Section: Discussionmentioning

confidence: 99%

The Role of Vibrational Anharmonicity in the Computational Study of Thermal Spin Crossover

Sousa

Graaf

2019

Magnetochemistry

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“…For this reason, DFT calculations cannot evaluate Γ directly but only a configuration-dependent Γ-term that we label as Γ c and define as where H elec is the energy of configuration c relative to the LS state and Δ H HL is the energy difference between the all-HS and all-LS states (i.e., all molecules in the same spin state). This equation can be obtained starting from eq and assuming that only H elec contributes to cooperativity. , This is a good assumption considering how the remaining terms are usually evaluated computationally. Due to the size of the SCO molecules, exchange interactions between the metal spins are generally neglected, and the spins are regarded as completely localized.…”

Section: Methodsmentioning

confidence: 99%

“…This equation can be obtained starting from eq 1 and assuming that only H elec contributes to cooperativity. 40,41 This is a good assumption considering how the remaining terms are usually evaluated computationally. Due to the size of the SCO molecules, exchange interactions between the metal spins are generally neglected, and the spins are regarded as completely localized.…”

Section: Methodsmentioning

confidence: 99%

“…Up to now, the theoretical analysis of cooperativity was mostly restricted to phenomenological approaches such as the Slichter and Drickamer (SD) model, ,− or the Ising model. ,− However, all these studies have in common that the model parameters either are evaluated using very simple expressions or are obtained from the fit of experimental values thus limiting their predictive power. Only recently, the development and proper benchmark of the DFT+ U +D2 scheme − allowed the evaluation of the model parameters using quantum chemical calculations incorporating structural and electronic degrees of freedom. , In these works, a methodology to study the cooperativity of SCO systems was proposed, and the well-known complex Fe(phen) 2 (NCS) 2 (phen = phenanthroline) was analyzed at the LDA+ U +D2 and GGA+ U +D2 levels. Interestingly, a reasonable estimate for the phenomenological interaction parameter Γ could be obtained from first-principles calculations.…”

Section: Introductionmentioning

confidence: 99%

“…Only recently, the development and proper benchmark of the DFT+U+D2 scheme 37−39 allowed the evaluation of the model parameters using quantum chemical calculations incorporating structural and electronic degrees of freedom. 40,41 In these works, a methodology to study the cooperativity of SCO systems was proposed, and the well-known complex Fe(phen) 2 (NCS) 2 (phen = phenanthroline) was analyzed at the LDA+U+D2 and GGA+U+D2 levels. Interestingly, a reasonable estimate for the phenomenological interaction parameter Γ could be obtained from first-principles calculations.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Cooperativity in Spin Crossover Systems. An Atomistic Perspective on the Devil’s Staircase

Vela

Paulsen

2018

Inorg. Chem.

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Cooperativity is key in defining the shape (i.e., gradual, abrupt, or hysteretic) of thermally driven spin transitions in magnetic switches. Despite its importance, there is very little information on its atomistic origin, which hinders the rational design of materials displaying a bistability region (i.e., hysteresis). In this paper, we investigate the spin transition of two solvatomorphs of [Fe(2-pic)]Cl, an Fe(II)-complex displaying thermal spin crossover (SCO) from a low-spin (LS) to a high-spin (HS) state with either gradual or abrupt two-step character. To do it, we apply a novel computational protocol to study the cooperativity of SCO compounds from DFT calculations, which does not rely on a priori assumptions on the studied system. The distinct shape of the spin transition is successfully captured, and the atomistic origin of cooperativity is traced back to geometrical distortions of the Fe-N core in case of the solvatomorph exhibiting an abrupt transition. According to our calculations, HS and LS molecules contribute differently to cooperativity, which results in a complex energetic evolution of the spin transition that cannot be described by the common Slichter-Drickamer model. The present work opens new avenues for the study of cooperativity of SCO systems having a chemically oriented perspective and demonstrates that quantum chemistry calculations can discriminate the shape of a spin transition, while providing insight into the atomistic underlying factors that contribute to its cooperative behavior.

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Intermolecular Interaction Tuning of Spin-Crossover Iron(III) Complexes with Aromatic Counteranions

et al. 2018

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Iron(III) spin-crossover (SCO) complexes [Fe(qsal)]BS·MeOH·HO (1), [Fe(qsal)](NS)·MeOH (2), [Fe(qnal)](NS) (3), and [Fe(qnal)]PS·MeOH·CHCl (4) (Hqsal, N-(8-quinolinyl)salicylaldimine; Hqnal, N-(8-quinolinyl)-2-hydroxy-1-naphthaldimine; BS, benzenesulfonate; NS, 1-naphthalenesulfonate; PS, 1-pyrenesulfonate) have been synthesized and characterized by X-ray structure determinations and temperature-dependent magnetic susceptibility measurements. The aromatic counteranions BS, NS, and PS can be used for the tuning of intermolecular coupling through a variety of weak interactions. All of the complexes show temperature-dependent SCO behavior. but the light-induced excited spin-state trapping (LIESST) effect was observed only for 1, 3, and 4 when the samples were illuminated (λ 808 nm) for 1 h at 5 K. In particular, 59% of the LS form of 1 was converted to the metastable HS state by illumination, equal to the highest degree of conversion yet known for LIESST in [Fe(qsal)] derivatives. The lack of a LIESST effect for 2 may be due to the relatively limited degree of interaction between the cations and anions in the lattice, reflected in a much longer minimum Fe···Fe separation in this complex in comparison to the others.

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

Cited by 8 publications

References 44 publications

The Role of Vibrational Anharmonicity in the Computational Study of Thermal Spin Crossover

The Role of Vibrational Anharmonicity in the Computational Study of Thermal Spin Crossover

Cooperativity in Spin Crossover Systems. An Atomistic Perspective on the Devil’s Staircase

Intermolecular Interaction Tuning of Spin-Crossover Iron(III) Complexes with Aromatic Counteranions

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