X-ray absorption spectroscopy study of the electronic structure and local coordination of 1st row transition metal-promoted Chevrel-phase sulfides |
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| Authors: | Joseph T Perryman Forrest P Hyler Jessica C Ortiz-Rodríguez Apurva Mehta Ambarish R Kulkarni |
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| Institution: | 1. Department of Chemistry, University of California, Davis, Davis, CA, USA;2. Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA, USA;3. Department of Chemical Engineering, University of California, Davis, Davis, CA, USA |
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| Abstract: | AbstractThe electronic structures of S and Mo as well as the local coordination of Mo are investigated as a function of metal promotion Chevrel-phase (CP) sulfides. We observe the effect of metal promoter-induced electron donation into the stoichiometric range MxMo6S8 (M?=?Fe, Ni, Cu; x?=?0–2) through analysis of X-ray absorption near-edge structure regions. We further observe the effect of this promotion on the bonding environment of Mo6 metal centers through extended X-ray absorption fine structure analysis. We monitor expansion and contraction of Mo6 octahedra with and without metal promotion, as has been predicted by Hückel molecular orbital theory. We further observe a marked tunability in the electronic structure of sulfur upon charge transfer between promoting species and Mo6S8 units. Average Mo6 octahedron Mo–Mo bond contraction from 2.76 Å to as short as 2.69 Å was observed upon incorporation of metal promoters, while intercluster separation displays a pronounced increase for promoter-host lattices compared to un-promoted Mo6S8. To corroborate spectroscopically observed phenomena, we performed computational analyses of spin-polarized densities of state for the CP materials investigated herein, where a detectable increase in sulfur-based frontier orbital population is observed in accordance with experimentally validated orbital filling. |
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| Keywords: | Chevrel-phase X-ray absorption DFT coordination electronic structure |
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