Mn K-Edge XANES and K XES Studies of Two Mn-Oxo Binuclear Complexes: Investigation of Three Different Oxidation State

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• 作者：Hendrik Visser ; Elodie Anxolabé ; hè ; re-Mallart ; Uwe Bergmann ; Pieter Glatzel ; John H. Robblee ; Stephen P. Cramer ; Jean-Jacques Girerd ; Kenneth Sauer ; Melvin P. Klein ; and Vittal K. Yachandr
• 刊名：Journal of the American Chemical Society
• 出版年：2001
• 出版时间：July 25, 2001
• 年：2001
• 卷：123
• 期：29
• 页码：7031 - 7039
• 全文大小：190K
• 年卷期：v.123,no.29(July 25, 2001)
• ISSN：1520-5126

文摘

Two structurally homologous Mn compounds in different oxidation states were studied to investigatethe relative influence of oxidation state and ligand environment on Mn K-edge X-ray absorption near-edgestructure (XANES) and Mn K X-ray emission spectroscopy (K XES). The two manganese compounds arethe di--oxo compound [L'₂Mn^IIIO₂Mn^IVL'₂](ClO₄)₃, where L' is 1,10-phenanthroline (Cooper, S. R.; Calvin,M. J. Am. Chem. Soc. 1977, 99, 6623-6630) and the linear mono--oxo compound [LMn^IIIOMn^IIIL](ClO₄)₂,where L^- is the monoanionic N,N-bis(2-pyridylmethyl)-N'-salicylidene-1,2-diaminoethane ligand (Horner, O.;Anxolabéhère-Mallart, E.; Charlot, M. F.; Tchertanov, L.; Guilhem, J.; Mattioli, T. A.; Boussac, A.; Girerd,J.-J. Inorg. Chem. 1999, 38, 1222-1232). Preparative bulk electrolysis in acetonitrile was used to obtain higheroxidation states of the compounds: the Mn^IVMn^IV species for the di--oxo compound and the Mn^IIIMn^IV andMn^IVMn^IV species for the mono--oxo compound. IR, UV/vis, EPR, and EXAFS spectra were used to determinethe purity and integrity of the various sample solutions. The Mn K-edge XANES spectra shift to higher energyupon oxidation when the ligand environment remains similar. However, shifts in energy are also observedwhen only the ligand environment is altered. This is achieved by comparing the di--oxo and linear mono--oxo Mn-Mn moieties in equivalent oxidation states, which represent major structural changes. The magnitudeof an energy shift due to major changes in ligand environment can be as large as that of an oxidation-statechange. Therefore, care must be exercised when correlating the Mn K-edge energies to manganese oxidationstates without taking into account the nature of the ligand environment and the overall structure of the compound.In contrast to Mn K-edge XANES, K XES spectra show less dependence on ligand environment. The K_1,3peak energies are comparable for the di--oxo and mono--oxo compounds in equivalent oxidation states.The energy shifts observed due to oxidation are also similar for the two different compounds. The study of thedifferent behavior of the XANES pre-edge and main-edge features in conjunction with K XES providessignificant information about the oxidation state and character of the ligand environment of manganese atoms.