Spin crossover in Fe(II) complexes: An ab initio study of ligand σ-donation

Authors

  • Alex Domingo,

    1. Departament de Química Física i Inorgànica, Universitat Rovira i Virgili, Marcel·lí Domingo s/n, 43007 Tarragona, Spain
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  • Maria Àngels Carvajal,

    1. Departament de Química Física i Inorgànica, Universitat Rovira i Virgili, Marcel·lí Domingo s/n, 43007 Tarragona, Spain
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  • Coen de Graaf

    Corresponding author
    1. Departament de Química Física i Inorgànica, Universitat Rovira i Virgili, Marcel·lí Domingo s/n, 43007 Tarragona, Spain
    2. Institució Catalana de Recerca i Estudis Avançats (ICREA), Passeig Lluís Companys 23, 08010 Barcelona, Spain
    • Departament de Química Física i Inorgànica, Universitat Rovira i Virgili, Marcel·lí Domingo s/n, 43007 Tarragona, Spain
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Abstract

The relative stability of high-spin and low-spin states has been studied in a series of Fe(II) complexes with model ligands of different σ donation strength. The natural (delocalized) orbitals are transformed to atomic-like orbitals to analyze the multiconfigurational wave function in a valence bond picture. This analysis reveals a direct relation between the stabilization of the low-spin state and the importance of the ligand-to-metal charge transfer in the σ orbitals. The multiconfigurational second-order perturbation theory (CASPT2) energy dependence of the low-spin state as function of the Fe-ligand distance deviates significantly from coupled cluster (CCSD(T)) calculations. This is ascribed to the intrinsic multiconfigurational character of the wave function of the low-spin state, invalidating the use of the simple closed-shell reference in the coupled cluster calculations. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

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