Electronic Structure of M(BH4)4, M = Zr, Hf, and U, by Variable Photon-Energy Photoelectron Spectroscopy and Density Functional Calculations

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• 作者：Jennifer C. Green ; Monica de Simone ; Marcello Coreno ; Aled Jones ; Helen M. I. Pritchard ; and G. Sean McGrady
• 刊名：Inorganic Chemistry
• 出版年：2005
• 出版时间：October 31, 2005
• 年：2005
• 卷：44
• 期：22
• 页码：7781 - 7793
• 全文大小：694K
• 年卷期：v.44,no.22(October 31, 2005)
• ISSN：1520-510X

文摘

Photoelectron (PE) spectra have been obtained for the M(BH₄)₄ (M = Zr, Hf and U) molecules in the 20-60 eVphoton-energy range, and for M = U, also in the 90-120 eV region. Derived branching ratios (BR) and relativepartial-photoionization cross sections (RPPICS) of the valence bands are used to confirm band assignment anddemonstrate d-orbital covalency for all three compounds and f-orbital covalency for U(BH₄)₄. Core ionizations areidentified and used to confirm resonance features in the RPPICS. The absorption spectrum of Zr(BH₄)₄ between20 and 60 eV shows 4p absorption at 35.5 eV, coincident with the 4p-4d resonance in the RPPICS of the 1e and2t₂ ionization bands of Zr(BH₄)₄. Less intense absorption bands at 32.5 and 33.8 eV correspond with shape resonancefeatures in the 1a₁ and 1t₂ PE bands. The RPPICS of the f band of U(BH₄)₄ shows two strong resonant featuresbetween 95 and 120 eV. Direct photoemission of the 5f electrons from U(BH₄)₄ results only in the observation ofthe ²F_5/2 ion state of [U(BH₄)₄]⁺, but in the 5d-5f resonant region, a weak band corresponding to the ²F_7/2 ion stateis also observed. The splitting of the 1t₂ band of U(BH₄)₄ is attributed to a small contribution of U 6p semi-coreelectrons to this MO. Density functional calculations give a good estimate of the pattern of ionization energies,although the calculated absolute values are lower than the experimental values, the first IE by 0.5 eV for Zr(BH₄)₄and Hf(BH₄)₄ and 1.0 eV for U(BH₄)₄. The MO compositions are in very good agreement with the deductions madefrom the BR and RPPICS analyses.