Single-Molecule Magnet Properties of Transition-Metal Ions Encapsulated in Lacunary Polyoxometalates: A Theoretical Study

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• 作者：Daniel Aravena ; Diego Venegas-Yazigi ; Eliseo Ruiz
• 刊名：Inorganic Chemistry
• 出版年：2016
• 出版时间：July 5, 2016
• 年：2016
• 卷：55
• 期：13
• 页码：6405-6413
• 全文大小：380K
• 年卷期：0
• ISSN：1520-510X

文摘

Single-molecule magnet (SMM) properties of transition-metal complexes coordinated to lacunary polyoxometalates (POM) are studied by means of state of the art ab initio methodology. Three [M(γ-SiW₁₀O₃₆)₂] (M = Mn^III, Fe^III, Co^II) complexes synthesized by Sato et al. (Chem. Commun. 2015, 51, 4081–4084) are analyzed in detail. SMM properties for the Co^II and Mn^III systems can be rationalized due to the presence of low-energy excitations in the case of Co^II, which are much higher in energy in the case of Mn^III. The magnetic behavior of both cases is consistent with simple d-orbital splitting considerations. The case of the Fe^III complex is special, as it presents a sizable demagnetization barrier for a high-spin d⁵ configuration, which should be magnetically isotropic. We conclude that a plausible explanation for this behavior is related to the presence of low-lying quartet and doublet states from the iron(III) center. This scenario is supported by ab initio ligand field analysis based on complete active space self-consistent field results, which picture a d-orbital splitting that resembles more a square-planar geometry than an octahedral one, stabilizing lower multiplicity states. This coordination environment is sustained by the rigidity of the POM ligand, which imposes a longer axial bond distance to the inner oxygen atom in comparison to the more external, equatorial donor atoms.