Spectrochemical Series and the Dependence of Racah and 10Dq Parameters on the Metal鈭扡igand Distance: Microscopic Origin

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• 作者：A. Trueba ; P. Garcia-Fernandez ; J. M. Garci虂a-Lastra ; J. A. Aramburu ; M. T. Barriuso ; M. Moreno
• 刊名：Journal of Physical Chemistry A
• 出版年：2011
• 出版时间：March 3, 2011
• 年：2011
• 卷：115
• 期：8
• 页码：1423-1432
• 全文大小：960K
• 年卷期：v.115,no.8(March 3, 2011)
• ISSN：1520-5215

文摘

The origin of the spectrochemical series and the different dependence of crystal-field splitting (10Dq) and Racah parameters on the metal鈭抣igand distance, R, is explored through ab initio calculations on Cr³⁺-doped K₂NaScF₆, Cs₂NaYCl₆, Cs₂NaYBr₆, and Cs₂NaYI₆ lattices. For this purpose both periodic and cluster calculations have been performed. An analysis of ab initio results proves that 10Dq values mostly come from the small admixture of deep n_Ls ligand orbitals present in the antibonding e_g(x²鈭?i>y²,3z²鈭?i>r²) level and not from the dominant covalency with valence n_Lp ligand orbitals, which is actually responsible for the reduction of Racah parameters. This study thus reveals the microscopic origin of the stronger dependence upon R of 10Dq when compared to that observed for Racah parameters, thus explaining why electronic transitions which are 10Dq-independent give rise to sharp optical bands. As a salient feature, while the covalency with n_Lp levels increases significantly on passing from CrF₆^{3鈭?/sup> to CrI₆3鈭?/sup>, the n_Ls admixture in e_g is found to be practically unmodified. This fact helps to understand the progressive decrease of 10Dq through the series of CrF₆3鈭?/sup>, CrCl₆3鈭?/sup>, CrBr₆3鈭?/sup>, and CrI₆3鈭?/sup> complexes embedded in the corresponding host lattices when compared at the corresponding equilibrium distance at zero pressure. The growing importance of the n_Ls admixture is well-depicted using deformation density diagrams on passing from the ground state 4A₂(t_2g3) to the 4T₂(t_2g2e_g) excited state depicted at several R values.}