Structural Analysis of Group V, VI, and VII Metal Compounds by XAFS

Abstract

The characteristics of K-, L1-, and L3-edges of XANES (X-ray Absorption Near Edge Structure) spectra of group V, VI, and VII compounds, which have different coordination number, number of d electrons, and the coordination sphere symmetry, have been classified. Two p → d transitions were observed in the second derivative plots of the L3-edge XANES spectra for the group V, VI, and VII compounds. These two transitions can be assigned to split d orbitals. The splitting and area of the two white lines depends on the symmetry of coordination sphere because the splitting corresponds to the crystal field splitting of d orbitals. The splitting of d orbitals is correlated with the pre-edge peak area of K or L1-edge XANES spectra, which are attributed to the dipole forbidden s → d transition and occur from the mixing of p and d orbitals. This correlation is supported by DFT calculations of several groups of V, VI, and VII structural models (being four-, five-, and six-coordinated, respectively). Clarifying the correlation between the splitting of the white line and structure of group V, VI, and VII metal compounds is important for providing structural information about unknown group V, VI, and VII metal sites.

Solution X-Ray Absorption Spectroscopy (XAS) for Analysis of Catalytically Active Species in Reactions with Ethylene by Homogeneous (Imido)vanadium(V) Complexes—Al Cocatalyst Systems

“…Geometries toward the Pre-Edge Peak Intensity, and the Edge Absorption in the XANES Spectra It has been known that the pre-edge peak intensity and the edge absorption (peak) in the V-K edge XANES spectra are influenced by the oxidation state and basic geometry around vanadium [49][50][51][52]. This is because that transition of a 1s electron to 3d orbital is the electric quadrupole transition (giving weak pre-edge absorptions), and an intense pre-edge peak is assigned to an electric dipole transition to the p-character in the d-p hybridized orbital; simple estimation of the pre-edge peak intensity could be thus possible from the character tables of group theory [50,51].…”

“…These vanadium(V) complexes show similar pre-edge peak positions (5468.4 eV in VO(O i Pr)3, 5465.6 eV (and 5467.1 eV) in V(NAd)Cl3 [19], at 5465.0 eV (and 5466.8 eV) in V(NAr)Cl3 [19], 5468.1 eV in V(NAr)(OAr)3 [23], and 5466.8 (and 5465.3) eV in V(NAr)Cl2(OAr) [21]), which are considered as due to a transition from 1s to 3d + 4p [25,26,49,50]; the curve-fitting of XANES [53], V(NAr)Cl 3 [54], V(NAr)(OAr) 3 [55], and V(NAr)Cl 2 (OAr) [56]; Ad = 1-adamantyl, and Ar = 2,6-Me 2 C 6 H 3 ) in toluene at 25 • C, and the spectrum of V IV (NAd)Cl 2 (NHMe 2 ) 2 [45] is shown for comparison. These vanadium(V) complexes show similar pre-edge peak positions (5468.4 eV in VO(O i Pr) 3 , 5465.6 eV (and 5467.1 eV) in V(NAd)Cl 3 [19], at 5465.0 eV (and 5466.8 eV) in V(NAr)Cl 3 [19], 5468.1 eV in V(NAr)(OAr) 3 [23], and 5466.8 (and 5465.3) eV in V(NAr)Cl 2 (OAr) [21]), which are considered as due to a transition from 1s to 3d + 4p [25,26,49,50]; the curve-fitting of XANES spectrum of V(NAd)Cl 3 is in good agreement with that estimated by the DFT (density functional theory) calculation [19]. Strong pre-edge peak intensities observed especially in VO(O i Pr) 3 and V(NAr)(OAr) 3 are due to their tetrahedral (T d ) geometry around vanadium (formation of d-p hybridized orbital through 1s-3d transition), as described above [25,26,49,50].…”

“…These vanadium(V) complexes show similar pre-edge peak positions (5468.4 eV in VO(O i Pr) 3 , 5465.6 eV (and 5467.1 eV) in V(NAd)Cl 3 [19], at 5465.0 eV (and 5466.8 eV) in V(NAr)Cl 3 [19], 5468.1 eV in V(NAr)(OAr) 3 [23], and 5466.8 (and 5465.3) eV in V(NAr)Cl 2 (OAr) [21]), which are considered as due to a transition from 1s to 3d + 4p [25,26,49,50]; the curve-fitting of XANES spectrum of V(NAd)Cl 3 is in good agreement with that estimated by the DFT (density functional theory) calculation [19]. Strong pre-edge peak intensities observed especially in VO(O i Pr) 3 and V(NAr)(OAr) 3 are due to their tetrahedral (T d ) geometry around vanadium (formation of d-p hybridized orbital through 1s-3d transition), as described above [25,26,49,50]. In addition to the pre-edge peaks, the XANES spectra in V(NAd)Cl 3 , V(NAr)Cl 3 , and V(NAr)Cl 2 (OAr) showed a "shoulder-edge absorption" (marked in circle at 5476.7, 5477.6, and 5475.7 eV, respectively), which are considered to be ascribed to an absorption of the V-Cl bond [25,26,57].…”

Order within disorder: The atomic structure of ion-beam sputtered amorphous tantala (a-Ta2O5)

“…In addition, X-ray absorption near edge spectroscopy (XANES) may also provide additional insights into the coordination and electronic structure. 37,38 We anticipate that these studies will lead to further understanding of the changes induced in the coating atomic structure during common IBS coating manufacturing processes, such as annealing and doping, and stimulate further study into correlations with optical and mechanical losses.…”

Direct observation of fractional change of niobium ionic species in a solution by means of X‐ray absorption fine structure spectroscopy

“…X‐ray absorption fine structure spectrum of transition metal around the near edge region is a promising tool to probe unoccupied d states. The pre‐edge peak intensity in the K‐edge X‐ray absorption near edge structure (XANES) of 3d and 4d transition metals is a good measure of coordination symmetry, and the L 2,3 ‐edge XANES spectrum reflects the local coordination and the valence of the X‐ray absorbing atoms . An L 3 ‐edge XANES spectrum from d 0 ion has two prominent peaks corresponding to the crystal field splitting of d orbitals, and the XAFS spectra were utilized to confirm the tetrahedral coordination of Mo(VI) in zeolites and to analyze the local structural changes of WO 3 species …”