Guidelines for the Molybdenum Oxidation State and Geometry from X-ray Absorption Spectroscopy at the Mo L_2,3-Edges

Abstract

Molybdenum accepts oxidation states from -II to +VI. This versatility is highly beneficial for applications in catalysis, especially combined with sulfur to form the ubiquitous MoS 2 material. X-ray Absorption Near Edge Spectroscopy (XANES) is a particularly welladapted technique to study simultaneously both elements, since the K-edge of S (2472 eV) and the L 2,3 -edges of Mo (2520 -2625 eV) have similar absorption energies. It provides information on both the electronic and local structure of metal-containing species and allows drawing structure-activity relationships. However, L 2,3 -edges are difficult to interpret, especially for 4d and 5d transition metals. In addition, only few recent studies focus on the measurement of the signal of Mo-based reference compounds, meaning that the references from the literature do not benefit from recent technical progress. Notwithstanding theoretical tools that allow a deep understanding of such spectroscopic data, the lack of reference spectra prevents a quick yet reliable interpretation. In this work, we provide a method for the interpretation of X-ray absorption near edge structure (XANES) data at the Mo L 2,3 -edges, based on a library of spectra of simple Mo compounds. From our analysis, we suggest using the L 3 -edge to determine the oxidation state (in selected cases) and the L 2 -edge to gain insight on geometry around the Mo atoms. This method is then applied to a series of molybdenum sulfides compounds in order to rationalize their structures. Besides this example, these guidelines should help to qualitatively interpret XANES of Mo at L 2,3 -edges in future studies.

Structural Studies and Thermal Analysis in the Cs2MoO4–PbMoO4 System with Elucidation of β-Cs2Pb(MoO4)2

“…If the center of inversion on Mo is lost by distortion of an octahedron or switching to tetrahedral symmetry, hybridization of 4d with 5p causes a preedge to appear. 34 In the molybdates, this extra edge feature is more pronounced than that in MoO 3 . In MoO 3 , this is observed as a shoulder due to core–hole broadening; the broadening comes from the hybridization of O 2p with Mo 4d and Mo 5p.…”

“…If the center of inversion on Mo is lost by distortion of an octahedron or switching to tetrahedral symmetry, hybridization of 4d with 5p causes a preedge to appear . In the molybdates, this extra edge feature is more pronounced than that in MoO 3 .…”

Structural engineering and electronic state tuning optimization of molybdenum-doped cobalt hydroxide nanosheet self-assembled hierarchical microtubules for efficient electrocatalytic oxygen evolution

“…), the second peak (B) has greater intensity [49,50]. With the prolongation of the reaction time, the peak A weakened and the peak B enhanced, indicating that the coordination structure of Mo ions in the material was transformed from octahedral to tetrahedral.…”

Highly Efficient β‐Functionalized Oxidomolybdenum(V) Corroles for Catalytic Oxidative Bromination of Phenols at Room Temperature

“…Molybdenum is a 4 d transition element that exists in oxidation states ranging in –II to +VI, having coordination numbers varying from 4 to 8 in several geometries [1−3] . This versatility in coordination number and oxidation state makes it highly favourable for catalytic applications like hydrodesulfurization, [4] oxidative bromination, [5] hydrogen evolution reaction, [6] epoxidation, [7] oxidation of alkanes, [8] olefin metathesis [9] and so on.…”