Molybdenum-Pterin Chemistry. 3. Use of X-ray Photoelectron Spectroscopy To Assign Oxidation States in Metal Complexes of Noninnocent Ligands

详细信息    查看全文

• 作者：Sharon J. Nieter Burgmayer ; Heather Layton Kaufmann ; Giuseppino Fortunato ; Paul Hug ; and Berthold Fischer
• 刊名：Inorganic Chemistry
• 出版年：1999
• 出版时间：May 31, 1999
• 年：1999
• 卷：38
• 期：11
• 页码：2607 - 2613
• 全文大小：216K
• 年卷期：v.38,no.11(May 31, 1999)
• ISSN：1520-510X

文摘

A series of molybdenum-pterin complexes produced from reactions of molybdenum and pterin reagents in variousoxidation states has been investigated by X-ray photoelectron spectroscopy (XPS). Prior difficulties in makingoxidation state assignments for the metal center and coordinated pterin can be resolved through comparison ofMo 3d binding energies (BE) for these new complexes with the BEs of standard molybdenum complexes. XPSanalysis of molybdenum-pterin complexes produced from reactions of Mo(VI) reagents with tetrahydropterinsshow binding energies that are shifted by 1.5-1.8 eV to lower energies as compared to the BEs observed for theoxo-Mo(VI) reagents. The opposite shift in BE values is observed for complexes prepared from Mo(IV) chlorideand fully oxidized pterins where BEs shift to higher values with respect to those for the starting Mo(IV) reagents.Remarkably, the BEs obtained for Mo-pterin complexes originating from Mo(VI)-tetrahydropterin reactionsare nearly identical with those from Mo(IV)-oxidized pterin reactions. Both shifts are consistent with a Mo oxidationstate of approximately +5. Both results indicate a significant delocalization of electron density over themolybdenum-pterin framework. This electronic redistribution is bidirectional since in the first system electrondensity flows from the reduced pterin to Mo(VI) and in the second case it flows from the Mo(IV) center to theelectron-deficient oxidized pterin. Also described are syntheses of several tris(pteridine) complexes of Mo(0) thatare diamagnetic molecules having intense MLCT absorptions near 500 nm. The electronic spectroscopic propertiessuggest that the pterin ligands in these complexes behave as strong pi-acids for Mo(0). This idea is verified byXPS analysis of Mo(piv-pterin)₃, where higher BEs are observed than for standard Mo(0) or Mo(+2) compounds.X-ray photoelectron spectroscopy may be one of the optimal spectroscopic tools for studying the poorly understoodelectronic interactions of molybdenum and pteridine heterocycles.