Probing the Molecular Orbitals and Charge Redistribution in Organometallic (PP)Pd(XX) Complexes. A Pd K-Edge XANES Study

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• 作者：Moniek Tromp ; Jeroen A. van Bokhoven ; Gino P. F. van Strijdonck ; Piet W. N. M. van Leeuwen ; Diek C. Koningsberger ; and David E. Ramaker
• 刊名：Journal of the American Chemical Society
• 出版年：2005
• 出版时间：January 19, 2005
• 年：2005
• 卷：127
• 期：2
• 页码：777 - 789
• 全文大小：649K
• 年卷期：v.127,no.2(January 19, 2005)
• ISSN：1520-5126

文摘

Pd K-edge X-ray absorption near-edge spectroscopy (XANES) is used to probe the unoccupiedmolecular orbitals in bidentate diphosphine Pd complexes. Complexes containing a series of bidentatediphosphine ligands (PP) are examined to study the effect of the ligand bite angle on the charge redistributionin these complexes. Different coordinating moieties (XX) have been used to induce a range of Pd oxidationstates. A full interpretation of the Pd K-edge XANES data is presented. The negative second derivative ofthese XANES data provides direct information on the energy and electronic distribution of the differentunoccupied molecular orbitals probed. The charge redistributions within the complexes, as reflected in theeffective Pd oxidation state, are indicated by both the intensity of the first edge feature, the "Pd d peak",and the energy of the second edge feature, the "Pd p peak", which can be easily observed in the negativesecond derivative of the XANES data. Additionally, the changing covalent interaction between the Pd andcoordinated moieties via the Pd p orbitals is reflected directly in the energy splitting of the "Pd p" peak.Thus, investigation of these (PP)Pd(XX) complexes, some used as catalysts in organic synthesis, withXANES spectroscopy provides new essential information on their electronic properties. Further, the XANESanalysis techniques described in this paper can be applied to investigate the unoccupied molecular orbitalsand charge redistributions within a wide range of samples.