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Open AccessFeature PaperArticle

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

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Departament de Química Física i Inorgànica, Universitat Rovira i Virgili, Marcel·lí Domingo 1, 43007 Tarragona, Catalonia, Spain
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Departament de Ciència de Materials i Química Física, Institut de Química Teòrica i Computacional, Universitat de Barcelona, C/ Martí i Franquès 1, 08028 Barcelona, Catalonia, Spain
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ICREA, Passeig Lluís Companys 23, 08010 Barcelona, Catalonia, Spain
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Author to whom correspondence should be addressed.
Magnetochemistry 2019, 5(3), 49; https://doi.org/10.3390/magnetochemistry5030049
Received: 27 July 2019 / Revised: 27 August 2019 / Accepted: 29 August 2019 / Published: 2 September 2019
(This article belongs to the Special Issue Spin-Crossover Beyond the Immediate Tribute)
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. View Full-Text
Keywords: spin crossover; iron complexes; vibrational frequencies; transition temperature; DFT; anharmonicity spin crossover; iron complexes; vibrational frequencies; transition temperature; DFT; anharmonicity
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MDPI and ACS Style

Wu, J.; Sousa, C.; de Graaf, C. The Role of Vibrational Anharmonicity in the Computational Study of Thermal Spin Crossover. Magnetochemistry 2019, 5, 49.

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