X線分析の進歩38 別刷

3d X What is the Origin of Pre-edge Peaks in K-edge XANES Spectra of 3d Transition Metals: Electric Dipole or Quadrupole? Takashi YAMAMOTO Copyright The Discussion Group of X-Ray Analysis, The Japan Society for Analytical Chemistry

3d X What is the Origin of Pre-edge Peaks in K-edge XANES Spectra of 3d Transition Metals: Electric Dipole or Quadrupole? Takashi YAMAMOTO Department of Materials Science and Engineering, Kyoto University Sakyo-ku, Kyoto 606-8501, Japan (Received 7 December 2006, Revised 29 January 2007, Accepted 3 February 2007) The features of pre-edge peaks in K-edge XANES spectra of 3d transition metal compounds were classified by kinds of elements, the coordination numbers, the symmetry and the number of d-orbital occupied. The electric dipole and quadrupole contributions were reviewed based on polarized spectra, group theory, and theoretical calculations. The transition of a 1s electron to 3d orbital gives weak preedge peaks due to the electric quadrupole transition for any symmetries. An intense preedge peak is assigned to an electric dipole transition to p-character in the d-p hybridized orbital. The mixing of a metal 4p orbital with the 3d orbital strongly depends on the coordination symmetry, the degree of which is predictable with group theory. The polarized spectrum is effective for assignment of preedge peaks. [Key words] XANES, Pre-edge peak, 3d transition metals, Electric-dipole transition, Electric-quadrupole transition 3d K XANES d 1s d d-p p XANES d p 606-8501 38 45 Adv. X-Ray. Chem. Anal., Japan 38, pp.45-65 (2007)

XANES 3d 1. X XANES 3d K-edge XANES 1 1949 XANES white line Hanson 2 1924 Coster KMnO 4 X 3 Wong 4 Fig.1 Farges (a) (b) (c) normalized absorbance CsAlTiO 4 Rb 2 TiO 3 β-ba 2 TiO 4 Ba 2 TiOSi 2 O 7 (fresnoite) KNaTiO 3 Rb 2 Ti 4 O 9 neptunite perovskite benitoite K 2 Ti 2 O 5 rutile Ni 2.6 Ti 0.7 O 4 anatase K 6 Ti 2 O 7 Fig.1 4950 5000 5050 ENERGY (ev) Ti K-edge XANES spectra of titanium oxides containing four (a), five (b) and six coordinated Ti (c). (Reprinted from F.Farges et al. 5), Coordination chemistry of Ti(IV) in silicate glasses and melt. 1. XAFS study of titanium coordination in oxide model compounds Geochim. Cosmochim. Acta, 60, 3023, 1996, with permission from Elsevier.) 46 38

XANES Fig.2 5 FEFF 2.5 2 ev 5 6 7 8-11 TS-1 Bordiga Fig.3 12 (a) (b) NORMALIZED HEIGHT (c) (d) ABSOLUTE POSITION (ev) 0 20 40 60 80 100 Energy /ev Fig.2 Normalized pre-edge height versus energy position for Ti K-pre-edge features in authentic compounds with different coordination number. (Reprinted from F.Farges et al. 5), Coordination chemistry of Ti(IV) in silicate glasses and melt.1. XAFS study of titanium coordination in oxide model compounds Geochim. Cosmochim. Acta, 60, 3023, 1996, with permission from Elsevier.) Fig.3 Ti K-edge XANES spectra of Ti-incorporated zeolite TS-1 outgassed at 400 K (a), followed by dose of NH 3 (b), after adsorption-desorption procedure of NH 3 at room temperature (c), and TiO 2 (anatase) (d). (Reprinted with permission from S.Bordiga et al. 12), J. Phys. Chem., 98, 4125, 1994 American Chemical Society.) 38 47

400 K EXAFS PbTiO 3 763 K Miyanaga PbTiO 3 XAFS 13 EXAFS 3d K-edge XANES 1s-3d 1s 3d p XAFS XANES 3d K XANES 2. X X X 14 EXAFS XANES 14-16 48 38

+ + + - + - - - + + s p d Fig.4 The shape of typical atomic orbitals. 1s 1000 1 Kawai 17 Blair 18 Ψ f e Ψ i r p s p d Fig.4 s-p s-d j 0 ±1 l ±1 3. XANES Kronig 1950 Cotton 19 1s d p d p 20 21 Harris 22 70 Kawai 17 T d O h D 4h d Fig.5 p d Table 1 T d t 2 p O h p d T d d p O h D 4h e g p d 1s p-d 3d p 14,17,23 38 49

b 1g e g t 2 b 2g e t 2g a 1g e g T d O h D 4h Fig.5 Crystal field splitting of d-orbitals with different symmetries. Table 1 Lists of character tables. T d O h D 4h p d p d p d A 1 x 2 + y 2 + z 2 A 1g x 2 + y 2 + z 2 A 1g x 2 + y 2, z 2 A 2 A 2g A 2g R z E (2z 2 -x 2 -y 2, x 2 -y 2 ) E g (2z 2 -x 2 -y 2, x 2 -y 2 ) B 1g x 2 -y 2 T 1 (R x, R y, R z ) T 1g (R x, R y, R z ) B 2g xy T 2 (x, y, z) (xz, yz, xy) T 2g (xz, yz, xy) E g (R x, R y ) (xz, yz) A 1u A 1u A 2u A 2u z E u B 1u T 1u (x, y, z) B 2u T 2u E u (x, y) p d p 1s p d d T d 4. Fig.1(c) XANES 50 38

XANES 1990 ev XANES EXAFS 15 DV-Xα IVO FEFF Fermi 15 EXAFS Rehr FEFF FEFF8 XANES 24 FEFF8 XAFS 25 5. 3d XANES 5.1 XANES Fig.1 4 6 Fig.6 14 5.2 3d Linqvist-Reis Fig.6 26 t 2g e g Fig.1 3 Fig.7 Yoshida 27 38 51

S5 ScO 7 4490 4495 S4 S3 ScO 6 ScO 6 Normalized absorbance S2 S1 L1 ScO 6 ScO 8 4460 4480 4500 4520 4540 4560 4580 4600 Energy / ev Fig.6 Sc K-edge XANES spectra of trivalent compounds. S1: [Sc(OH 2 ) 8 ](CF 3 SO 3 ) 3, S2: [Sc(OH 2 ) 6 ](ClO 4 ) 3, S3: [Sc(OH 2 ) 6 ] [Sc(OSO 2 CH 3 ) 6 ], S4: [Sc(OH 2 ) 4 (C 7 H 7 SO 3 ) 2 ] C 7 H 7 SO 3 2H 2 O, S5: [Sc 2 (µ- OH) 2 (OH 2 ) 10 ]Br 4 2H 2 O, L1: Sc(ClO 4 ) 3 in HClO 4 aqueous solution. (P.Linqvist-Reis et al. 26), Dalton Trans, 3868 (2006). Reproduced by permission of The Royal Society of Chemistry.) VO(OiPr) 3 (V 5+ 27) O 4 ) V 2 O 5 (V 5+ 27) O 5 ) MgV 2 O 6 (V 5+ 27) O 6 ) VO 2 (V 4+ O 6 ) V 2 O 3 (V 3+ O 6 ) Photon energy /ev Fig. 7 V K-edge XANES spectra of vanadium compounds. (Reproduced from S. Yoshida and T.Tanaka 27), in X-Ray Absorption Fine Structure for Catalysts and Surfaces, Chapter 8.2, pp. 304-325, Ed. Y.Iwasawa, 1996 World Scientific.) Fig.8 Fujidala 28 Fig.9 Yamamoto 29 52 38

Fig. 8 Cr K-edge XANES spectra of chromium compounds. (Reprinted from K.L.Fujdala and T.D.Tilley 28), Thermolytic molecular precursor routes to Cr/Si/Al/O and Cr/Si/Zr/O catalysts for the oxidative dehydrogenation and dehydrogenation of propane, J. Catal., 218, 123, 2003, with permission from Elsevier.) Fig.9 Mn K-edge XANES spectra of authentic compounds. MgV 2 O 6 Na 6 V 10 O 28 Tanaka 30 VO 2 V 2 O 3 38 53

(4O) (2N, 3O) (2N, 4O) [Fe(OC 10H 13) 4] - Fe(saloph)catH [Fe(salen)cat] - 0 40 Photon energy / ev Fig.10 Fe K-edge XANES spectra of high-spin Fe(III) complexes compounds with 4, 5 and 6-fold coordination. (Reproduced from A.L.Roe et al. 31), J. Am. Chem. Soc., 106, 1676, 1984 American Chemical Society.) 3d VIII Fig.10 Roe XANES 31 4 6 32,33 32 Bordiga SrFeO 4 0.55 34 Farges 35 KMnO 4 d VIII Rodriguez Fig.11 36 α-comoo 4 (CoO 6 ) CoAl 2 O 4 (CoO 4 ) Photon Energy (ev) Fig.11 Co K-edge XANES spectra of divalent compounds. (Reproduced from J.A.Rodriguez et al. 36), J. Phys. Chem. B, 102, 1347, 1998 American Chemical Society.) 54 38

NiCr 2 O 4 (NiO 4 ) KNiPO 4 (NiO 5 ) NiO (NiO 6 ) 8360 8400 Photon energy /ev Fig.12 Ni K-edge XANES spectra of nickel oxides with 4, 5 and 6-fold coordination. (Reproduced from F. Farges 35), Phys. Rev. B, 71, 155109, 2005 by the American Physical Society.) Fig.13 Cu K-edge XANES spectra of copper compounds. CuAl 2 O 4 contains 66.5% T d and 33.5% O h Cu 2+ species 37). Farges Fig.12 7 Yamamoto Fig.13 37 CuAl 2 O 4 66.5 33.5 % 3d Fig.14 XANES Cotton 38 Fig.14 Zn K-edge XANES spectra of divalent compounds. 38 55

5.2 d d Garcia 10 d Fig.15 d 0 d d 10 d 2 Fe 6+ Cr 4+ d d 3d 1s-3d d p-d p Farges 0.8-0.9eV 2 Georg Hight of preedge peak 1 1.0 0.8 0.6 0.4 0.2 0.0 V 5+ Mn 7+ Cr 6+ Ti 4+ Cr 5+ Fe 6+ Cr 4+ Mn 2+ Fe 3+ MO 4 MCl 4 Fe 2+ Co 2+ N i 2+ Cu 2+ Zn 2+ 0 1 2 3 4 5 6 7 8 9 10 Number of 3d electron Fig.15 Dependence of preedge peak height of tetrahedral compounds on the number of d-orbital. Ti 4+ : ref.5 (chloride: ref.40), V 5+ : ref.30, Cr n+ : ref.39, Mn 2+ : ref.35, Mn 7+ : ref.29, Fe 2,3+ : ref.6 (chloride: ref.23), Fe 6+ : ref.34, Co 2+ : ref.36, Ni 2+ : ref.7, Cu 2+ : ref.44, Zn 2+ : this work. 56 38

1.6 ev 40 d Tanaka 27,41 t 2g e g d 8 Modrow FEFF CoO MnO d-dos p 42 Vedrinskii NiO 4 ev 43 5.3 d-p p Sano Cl-Cu-Cl [CuCl 4 ] 2- XANES Absorption (arbitrary unit) Cl-1 (0 ) Cl-2 (35.7 ) Cl-3 (51.6 ) Cl-4 (67.9 ) 44 Fig.16 0 8974 ev Ψ p Ψ L 2 Ψ d Ψ L 2 8975 9000 Energy (ev) Fig.16 Cu K-edge XANES spectra of [CuCl 4 ] 2- compounds with different dihedral angles between the two Cl-Cu-Cl planes. Cl-1: [(C 6 H 5 ) CH 2 CH 2 NH 2 CH 3 ] 2 CuCl 4, Cl-2: [Pt(en) 2 Cl 2 ] CuCl 4, Cl-3: (N-phenyl-piperazinium) 2 CuCl 4, Cl-4: Cs 2 CuCl 4. (Reprinted with permission from M. Sano et al 44)., Inorg. Chem., 31, 459, 1992 American Chemical Society.) 38 57

8985 ev 4pπ Kosugi Yokoyama 45 Westre 49 XANES 23 DFT d Fig.17 Westre 23 3d 4p 4p Roe 28 31 Westre [FeCl 6 ] 3 - z 3d 2 z 4p z 23 Fe-Cl 2.1-2.6 4p z 4p z Fe 3+ Cl -- 2.46 O h C 4v p Westre total % Fe 4p mixing into 3d holes 8.0 6.0 4.0 2.0 Fe III Fe II 0.0 O h C 4V D 3h C 3V T d Symmetry Fig.17 Dependence of symmetry and valence of iron species on calculated total Fe 4p mixing into 3d molecular orbital. (Reproduced from T.E.Westre et al. 23), J. Am. Chem. Soc., 119, 6297, 1997 American Chemical Society.) 58 38

Fig.18 Qualitative molecular orbital analysis based upon density functional final state calculations of ferric complexes. Dotted arrows: electric quadrupole transitions; solid arrows: electric dipole + quadrupole transitions. (Reprinted from T.E.Westre et al. 23), J. Am. Chem. Soc., 119, 6297, 1997 American Chemical Society.) Fig.18 23 C 4v 20-22 p d a 1 (p z d z2 ) e (p x, y d xz, yz ) a 1 e a 1 p a 1 d 5.4 s XAFS 14-16 Fig.19 Penner-Hahn [CuCl 4 ] 2-- xy XANES 46 90 0 45 1s d 2-y2 x d 1/3 [Ni(CN) 4 ] 2-- D 4h XANES Kosugi z z 38 59

Fig.19 The polarized Cu K-edge XANES spectra for [CuCl 4 ] 2- and rotation angle dependency of the preedge-peak intensity. (Reprinted from J. E. Hahn et al. 46), Observation of an Electric Quadrupole Transition in the X-ray Absorption-Spectrum of a Cu(II) Complex, Chem. Phys. Lett., 88, 595, 1982 with permission from Elsevier.) Fig.20 Polarized Ni K-edge XANES spectra of K 2 Ni(CN) 4 2H 2 O single crystal and the powder spectrum. The z-axis is normal to the [Ni(CN) 4 ] 2- xy plane. (Reprinted from N. Kosugi et al. 47), Polarization dependence of XANES of square-planar [Ni(CN) 4 ] 2- ion - A comparison with octahedral [Fe(CN) 6 ] 4- and [Fe(CN) 6 ] 3- ions, Chem. Phys., 104, 449, 1986, with permission from Elsevier.) Fig.20 47 Hatsui z 2 A Ni 3d x -y2 * -- L x 2 -y 2 (5s) z B 1 B 2 Ni 4p z * + L z *(2π*) Ni 4p z * -- L z *(2π*) 60 38

16,48) B B 1 A T d V 2 O 5 Fig.7 V 2 O 5 V 3d O 2p Tullius 49 Wong 4 Tanaka 30 Grunes 50 Poumellec 51 Fig.21 Sipr V 2 O 5 XAFS 52 y x 70 z d xyz V = O z p z Dipole and quadrupole contributions to XANES 5 10 15 energy [ev] Fig.21 Polarized V K-edge XANES spectra of V 2 O 5 single crystal, and calculated dipole and quadrupole contributions. The z-axis is set to the direction of vanadyl oxygen. (Reprinted with permission from O. Sipr et al. 52), Phys. Rev. B, 60, 14115, 1999 by the American Physical Society.) 38 61

Absorption 2 4 6 8 10 12 Energy (ev) Fig.22 Polarized XANES spectra of TiO 2 (rutile) single crystal, results of theoretical calculations, _ and p z projected density states on Ti atom. Bottom: (ε, k)=([110],[110]) Top: (ε, k)=([001],[110]). Quadrupolar (q) and dipolar (d). (Reprinted with permission from Y. Joly et al. 55), Phys. Rev. Lett., 82, 2398, 1999 by the American Physical Society.) V 2 O 5 VO 6 V-O VO 5 VO x x=1-4 Poumellec V 2 O 5 VOPO 4 2H 2 O XANES 53 Fig.1 3d t 2g e g 54 Joly XANES finite difference method 55 Fig.22 FLAPW Ti 2p z A2 3 A1 p 62 38

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