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Stabilizing several anions (F, O, OH, S) in the vicinity
of transition metals or rare earths to tune the electronic properties of new materials Alain Demourgues CNRS, Université de Bordeaux, ICMCB, UPR9048, F Pessac, France GDR MEETICC Matériaux, Etats ElecTronIques et Couplages non-Conventionnels 28-31 Mars 2017, AEROCAMPUS, Latresne(33)
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The anions Xp- E (q) = q + q2 Mulliken-Jaffé (1935 – 1963)
(q) = E(q)/q = + 2 q : Electronegativity = 2E(q)/2q = 2 : Hardness= 1/Polarizability (Pearson) The anions Xp- + electronegative (q) S2- N3- Cl- O2- F- H OH- * (Green apatites) H- + O2- 2e- + OH- Ca5(PO4)3(F, OH, H) S2- N3- Cl- O2- F- + hard + polarizable * K. Hayashi and H. Hosono, J. Phys. Chem. Chem. Phys, 2016, 18, 323,
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Hard-Soft Acid-Base (HSAB) theory
Ralph Pearson (1960) Energy H+(1s0), Ti4+(3d0), K+, Ba2+, La3+ Hard acid : Soft acid : Fe2+(3d6), Cu+(3d10) Soft base : H-(1s2), S2-, I-, SO42-, CO32- Hard base : F-, O2-, OH-, Cl-, NH3 Hard-Hard or Soft-Soft AB react faster leading to stronger bonds !
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F Fluorine, a super-halogen ! The anomolous properties of Fluorine
Bond-Dissociation Energy (kJ.mol-1) CH3X HX X2 F Cl Br I 300 Only for X2 240 160 4 6 F- Fluorine is small in size and its supported charge is too high !
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S2- The M-X chemical bonding and the effect of mixed anions
Mq+ : Partial density of charges and oxydation states Point group ( Mq+ / Xp- ), anisotropy and networks Crystal field, Polarization, Covalency SO42- / PO43- / CO32-…? N3- Mq+ S2- F- H+/H- O2- A way to tune the ionicity-covalency of the chemical bonding and consequently the electronic properties !
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Ti Ce From 2D layers to 3D tunnel networks OH- O2- F- S2- 22 58
Outline Rare-Earth (Ce) oxy-fluoro-sulfides and Transition Metal (Ti) oxy-hydroxy-fluorides Composition, Structural features and Energy Gap From 2D layers to 3D tunnel networks OH- O2- F- Ti4+(J=0)/Ti3+(J=3/2) S2- Ti [Ar] 4s23d2 Pauling : 1.4 22 The key role of Electronegativity (), Charge (q+), Ionic radius (rion) of Mq+ to define local electrical field = (q)/ rion Ce4+(J=0)/Ce3+(J=5/2) Point group symmetry (M vs X), Mixing empty d orbitals with filled ligand p orbitals, Looking for non-bonding character Lowering the band gap Ce [Xe] 6s24f2 Pauling : 1.1 58 Second order Jahn-Teller distortion
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-La2S3 LaF3 La2O3 175 nm 230 nm 440 nm 2.7 2.1 1.8 abs
The mixed anions systems : absorption k() and refractive index n() - Electronegativity (Polarizability ) : F- > O2- > S2- -La2S3 LaF3 La2O3 175 nm 230 nm 440 nm 2.7 2.1 1.8 abs n(400 nm) - Modulation of the chemical bond : Ln-S/O/F : Variation of the absorption wavelength and refractive index - Competitive bonds around metals : anisotropy, modification of the chemical bonds and electronic properties
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A new class of compounds : rare earth oxyfluorosulfides
LaSF : abs = 440 nm (Eg = 2.8 eV) High absorption efficiency and refractive index UV Absorbers : abs = 400 nm (Eg = 3.1 eV) ?? Modification of rare earth environment Intergrowth of How to change the ionicity of blocks ? Size + Charge Ionic blocks [Ln2F2]4+ Covalent blocks [S2]4-
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X-Ray and Electron Diffraction
A new class of compounds : rare earth oxyfluorosulfides Modification of the size (ionicity) of ‘[Ln-O,F]’ blocks : double sulphur sheets Powder and Single crystal X-Ray and Electron Diffraction analysis [Ln3OF4]4+ [Ln2AF4]4+ [S2]4- [S2]4- 2 LnSF + AF2 Ln2AF4S2 (A= Ca, Sr) 2 LnSF + LnOF Ln3OF3S2 Tetragonal I4/mmm a 4 Å, c 19 Å Orthorhombic Pnnm a 5.6 Å, c 19 Å A. Demourgues et al. , J. Alloys Comp, 2001, 323, D. Pauwels, A. Demourgues et al .Solid State Sciences, 2002, 4,
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Powder X-ray and Neutron Diffraction analysis
A new class of compounds : rare earth oxyfluorosulfides Modification of the charge (ionicity) of ‘[Ln-O,F]’ blocks : single sulphur sheet Powder X-ray and Neutron Diffraction analysis [Ln2O1.5F]2+ [S]2- a c Ln2O1.5FS Hexagonal P-3m1 a 4.1 Å, c 6.9 Å D. Pauwels, A. Demourgues et al .Solid State Sciences, 2002, 4,
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Rare earth oxyfluorosulfides and optical absorption properties
d(La-O) 2.45 Å 4 d(La-S) 3 Å 3 300 400 500 600 700 800 10 20 30 40 50 60 70 80 90 100 % Reflexion Wavelength (nm) La2CaF4S2 LaSF La3OF3S2 La2SrF4S2 La2O1,5FS La2O2S La2O2S =La2O1.5FS d(La-O) 2.5 Å 4 d(La-S) 3 Å 5 LaSF La3OF3S2 La2AF4S2 A, Ln Relaxation of Sulphur sheets S-S distances Optical band gap 4f,5d(La) Number of S atoms Optical band gap 3p(S) [La(A)-F,O] blocks A/Ln-F/O bond distances
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The Ce valence states in fluorides, oxides and sulfides
J = 5/2 Low crystal field J = 0 High crystal field CeIII(4f1) CeIV (4f0) F2 H2 CeF3 Ce2S3 CeO2 CeSF CeOF Ce4O4S3 Ce4+/Ce3+ F- : (Pauling) = 4 Hard base O2- : (Pauling) = 3.5 Hard base Ce4O2F2S3 - Ce4O3FS3 S2- : (Pauling) = 2.6 Soft base High crystal field High Madelung Potential VO2- Low crystal field Low Madelung Potential VF-, VS2- Distorted Polyhedron [9] Ce-F = A Cubic site [8] Ce-O = 2.34 A Two tetrahedra surrounding Ce [8] Ce-S = A
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Which strategy to keep the Ce4+ valence state in oxyfluoride ?
From the composition and structural features of Ce compounds to the optical absorption properties 5 eV CeO2 Ce(5d) O(2p) 4f0 Ce4+ 3 eV S(3p) Ce(5d) Ce2S3/CeSF F(2p) CeF3 4f1 Ce3+ Ce(5d) F(2p) 2 eV 4f1 Ce3+ 7 eV 5 eV 3 eV CTB Which strategy to keep the Ce4+ valence state in oxyfluoride ?
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Chemical analysis Ce1-xCaxO2-x-y/2Fy
Ca2+ content F- rate The solid solution CeO2 (a = 5.41Å ) - CaF2 (a = 5.46 Å) - CaO Chemical analysis Ce1-xCaxO2-x-y/2Fy 5,4097 (1) a (Å) 5,4217 (4) Ce0,92Ca0,05Na0,03O1,91 Ce0,71Ca0,29O1,59F0.24 Diffuse reflectance % Wavelength (nm) % F, Ca Ionic character of Ce4+-O2- chemical bonding F- [4] : FCa2Ce2 and FCa3Ce major sites (19F MAS-NMR) 2p(O) 4f (Ce) Charge Transfer Band energy L. Sronek, A.. Demourgues et al. Chem. Mater. , 2007, 19, L. Sronek, A.. Demourgues et al. J. Phys. Chem. C, 2008, 112,
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Structural relationships with RE TM PN O1-xFx oxypnictides
LaFS = PbFCl = BiOCl Charge density into Layers ( LaO)+ -Fluorite- and ( FeAs)- -Anti Fluorite- e- Transfer : LaO1-xFxFeAs LaO « réservoir » layer FeAs conducting layer Takahashi, H. et al. Superconductivity at 43K in iron-based layered compound .LaO1-xFxFeAs. Nature, 2008, 453, (LaF)2+ layer (LaO)+ layer (S)2- layer (FeAs)- layer : B.I. Zimmer , W. Jeitschko et al. J. Alloys and Comp, 1995, 229, 238
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Structural parameters which influence superconducting
properties of REO1-xFxFeAs compounds Parameters which influence Tc : Doping with F- Increasing of electron density into FeAs layers Application of High Pressure 2D Structure and critical temperature Tc : Converging to Tetrahedron FeAs4 [Td] Symmetry Inter layers Fe2As2 distance increasing Reduction of cell parameters Compounds Tc CaFe1-xCox AsF 22 K Sr0,8La0,2FeAsF 36 K Sr0,5Sm0,5FeAsF 56 K 17
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From rare earth to transition metal :
the Fe2+ (3d6) case stabilized in mixed anions environment Sr2F2Fe2+2OS2 (Oh) FeO2S4 Sr2Fe2+CuO3Se [Perovskite layers] [5] FeO5 + [AntiFluorite sheets] [4] CuSe4 [Fluorite blocks] [Sr2F2]2+ + [ Anti CuO2 layers] [Fe2O (S2) ] 2- P4/nmm p-type (Cu+)-SC + AFM (TN>300K) H. Kabbour, L. Cario et al. J.A.C.S, 2008, 130, 8261 D. Berthebaud et al. Sol. Stat. Sci. 2014, 36, I4/mmm SC + 2D Ising AFM (TN<110K) S=2 AFM checkerboard spin lattice CaOFe2+S [Rocksalt blocks] [6] CaO3S3 + [Wutzite sheets] [4] FeOS3 (Td) FeOS3 Polar structure (P63mc), Magnetodielectric TN=35K C. Dellacotte et al. Inorg. Chem. 2015, 54,
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x (q) S2- O2- F- Polarizability OH- Transition Metal (Ti)
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[F-] > [O2-] > [OH-]
Ti-based hydroxy-fluorides with ReO3-derived network and band gap Ti vacancies distorted Oh site Stabilization of CB Ti(3d) electronegativity [F-] > [O2-] > [OH-] (ReO3) Ti0.75 0.25OH1.5F1.5 TiO2 BaTiO3 CB Ti(3d) CB Ti(3d) CB Ti(3d) O [3] Ti-O = Å CTB O [2] Ti-O = 2.00 Å O [2] Ti-OH-F = Å CTB CTB eV 3.2 eV 3.4 eV VB OH(2p) F(2p) VB O(2p) VB O(2p) A. Demourgues et al. Chem. Mater. 21, 2009,
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Ordered ReO3 supercell (SG : Pn-3m , a = 7.6177 A) Ti vacancies !
Ti-based hydroxy-fluoride with ReO3-derived network Electron (SG : Pn-3m) X Ray, Neutron (Atomic positions) diffraction investigations c* 002 Ordered ReO3 supercell (SG : Pn-3m , a = A) Ti vacancies ! 020 b* [100] 1.90 A 1.95 A 1.90 A 1.95 A 1.90 A [ Ti2/3 1/3 (OH/F)2 F/OH ]6 [Ti (F/OH)3]2 exp = 2.63 g.cm-3 (theo = 2.70 g.cm-3) A. Demourgues et al. Chem. Mater. 21, 2009,
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Structural features of Ti1-(O,OH,F)3 HTB
Ti0.93O0.7OH0.9F1.4, 0.27 H2O (TGA/density) Pnma, a=7.5581(1) Å, b= 7.322(1) Å, c= (2) Å Powder XRD Rietveld Refinement (Cu Kα = Å) Powder Neutron Rietveld Refinement (= Å, SINQ-SWI) 3 TiO2(OH,F)4 distorded octahedra (Neutrons) : Ti Å F1/F2/O2 Ti Å F1/O3/F3 Ti Å O1/F2/F3- Ti vacancies
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Energy gap and band diagram of Ti oxy-hydroxy-fluorides (HTB)
Solvothermal route : HTB- Ti0.93 0.07O0.7OH0.9F1.4 (Eg=3.42 eV) S. F. Matar (DFT calculation) Aqueous route : HTB-Ti0.8 0.2O0.2OH1.6F1.2 (Eg=3.35 eV) ReO3- Ti0.75 0.25OH1.5F1.5 (Eg=3.22 eV) CB Ti(3d) CTB OH(F)/Ti (O2- ) (Ti) Oh distortion O2- Disorder main species OH-/F- eV VB OH(2p)/O(2p) F(2p) Eg , E/k (direct transition)
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V/Mo/W substitution into Ti1-(O,OH,F)3 HTB to tune the O content
and enhance the TM site distortion Hydrothermal route (TiOCl2 , NH4VO3/(NH4)2MoO4/(NH4)6W12O39, aqueous HF(40%), R= HF/Ti= 1.7, water as solvent, T=90°C) x (0-5%) (a,c,V) and b : Ti and Oh distortion (SOJT)
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V/Mo/W substitution into Ti1-(O,OH,F)3 HTB
Structure refinement (Pnma hypothesis) Unit cell parameters and reliability factors (SG : Pnma) Undoped Sol-Gel route 10% V Aqueous route 10% Mo 10% W a (Å) b (Å) c (Å) 7.5581(1) 7.3922(1) (5) 7.5589(2) 7.3879(1) (3) 7.5538(2) 7.3833(5) 12.780(1) 7.5479(3) 7.3827(2) (8) Volume (Å3) (1) 713.89(1) 712.77(1) 710.19(1) Rp Rwp Bragg-R Chi2 22.0 20.8 8.35 5.65 15.6 15.3 7.05 2.16 14.4 12.0 6.70 2.61 14.9 14.1 6.28 4.89 Enhancement of TM (Ti4+/V5+) site distortion with shorter bond distances 0% 10% V 10% Mo 10% W Ti1 → F1 1.87(6) Ti1 → F2 1.99(5) Ti1 → O2 1.92(2) 1.76(1) 2.09(2) 1.931(6) 1.87(1) 1.92(1) 1.901(6) 1.79(1) 1.92(1) 1.875(4) Ti2 → F1 1.93(7) Ti2 → O3 2.13(3) Ti2 → F3 2.01(6) 2.04(1) 1.907(5) 1.94(1) 1.95(1) 2.030(7) 2.05(1) 2.03(1) 2.255(8) 1.939(2)
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10% Mo 5% Mo Mo substitution into Ti1-(O,OH,F)3 HTB
Clear evidence of Mo5+ by ESR : 3 various sites (Pnma hypothesis) 10% Mo 5% Mo 10%Mo The Mo5+ sites distribution in 3 various sites varies with the Mo rate (low Mo content : stabilization in the most distorted octahedra)
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From Ti-based oxy-hydroxy-fluorides with HTB-derived network
to blue conductive Anatase TiO2:F The key role of structural/electronic defects : ReO3 - Ti0.75(OH)1.5F1.5 TiO2 white (500°C-600°C) HTB - Ti0.93O0.7OH0.9F1.4 TiO2: F blue (500°C-600°C) TGA under Ar + Anatase
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ESR analysis XPS analysis Blue conductive Anatase TiO2:F
Strong UV and NIR absorption, conduction e- and Ti3+. ESR analysis XPS analysis
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%V (e-) %Nb (e-)(2%) then
Blue conductive Anatase TiO2:F, V/Nb doped Strong UV and NIR absorption, %V (e-) %Nb (e-)(2%) then
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Blue conductive Anatase TiO2:F, V/Nb doped
conduction e- (VO)2+ species (V4+, 3d1, I=7/2) V-doped TiO2:F XPS analysis conduction e- F1s ~685 eV 0.7% F and 2% Nb (Ti3+, 3d1) Nb-doped TiO2:F
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Anatase-TiO2 and orbital molecular diagram :
Generation of defects induced by mixed anions compounds * anti-bonding Ti4+ (eg) dxz dyz * anti-bonding Ti4+ (t2g) Non-bonding character of dxy orbitals, 4 interactions Ti4+ - Ti4+ at 3.04 Å dxy dxy non-bonding dxy (Ti) and p (O) levels with non-bonding character O(p) p non-bonding Dense pellet obtained by SPS (82%) (T=600°C, P=100 MPa) TiO2: Nb (2%) / F (1%) O(p) bonding Conductivity (RT) = 0.2 -1cm-1 Seebeck coefficient (RT) = -77V/K bonding
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Conclusions and future works
How to build mixed anions 2D network ? The simple key role of electronegativity and polarisability 1/ of elements Hard-Hard and Soft-Soft Acid-Base rules CN(X with higher ) = CN(M with lower ) The main networks : Ionic blocks (F/O) vs covalent sheets (S/Se) Fluorite, Perovskite, Rocksalt vs anti-Fluorite, anti-CuO2, Würtzite . The key role of F- : the highest and its anomalous properties ! Designing new compounds (tuning Mn+ oxidation states) 2D/3D Ribbons (S2-, O2-, F- ) vs 3D (OH-, O2-, F- ) tunnel networks Tuning the band gap and opto-electronic properties by playing with competitive bonds around Mn+ Precursors to generate defects into oxides
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Acknowledgments Mathieu Duttine, ICMCB Laetitia Sronek,
PhD, ICMCB(2007) Nicolas Penin, ICMCB Damien Dambournet, PhD ICMCB(2008) PHENIX, Paris Madhu Chennabassapa, Post-doc (2014) ICMCB Belto Dieudonné, Post-doc (2016) ICMCB Damien Pauwels, PhD, ICMCB (2003), St Gobain Etienne Durand, ICMCB Alain Tressaud, ICMCB
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Structural features of Ti1-(O,OH,F)3 HTB-Pnma
Atomic positions and bond distances Distances (Å) X-ray at T=293K Neutron at T=293K Ti1 → F1 1.87(6) 1.93(2) Ti1 → F2 1.99(5) Ti1 → O2 1.92(2) 1.88(1) Ti2 → F1 1.93(7) 1.90(3) Ti2 → O3 2.13(3) 1.96(1) Ti2 → F3 2.01(6) 1.92(3) Ti2 → H2 3.06(1) 3.06(5) Ti3 → O1 1.87(13)/1.92(13) 1.70(10)/2.11(10) Ti3 → F2 1.82(5) 1.94(5) Ti3 → F3 1.82(6) 1.92(5) Ti3 → H1 3.24(2) 3.20(10) O1 → F2 2.58(13)/2.67(13) 2.57(4)/2.88(4) O1 → F3 2.71(13)/2.56(13) 2.59(4)/2.82(4) O1 → H1 3.10(4) 3.09(11) F1 → F2 2.73(8)/2.74(9) 2.64(3)/2.82(3) F1 → O2 2.68(9)/2.68(9) 2.70(2)/2.69(3) F1 → O3 2.89(9)/2.86(9) 2.71(3)/2.75(32) F1 → F3 2.74(8)/2.83(9) 2.78(3)/2.62(3) F2 → O2 2.71(8)/2.82(8) 2.58(4)/2.88(3) F2 → F3 2.62(8) 2.73(4) F2 → O4 3.21(6) 3.04(3) F2 → H1 2.38(5) 2.28(10) O2 → H1 2.92(7) 3.06(12) O3 → O4 3.01(9)/2.80(9) 3.08(5) O3 → H1 2.70(7) 3.13(12) O3 → H2 1.44(7) 1.78(7) F3 → H1 3.17(6)/2.63(6) 2.51(10) F3 → H2 2.55(5) 2.49(4) O4 → H1 1.22(4) 0.88(12) O4 → H2 1.37(5) 1.38(9) H1 → H2 1.96(5) 1.96(14) Atom Site x y z Occ B (Å2) Neutrons (T=293K), λ= Å Space group : Pnma Unit Cells : a= 7.554(1) Å, b= 7.383(2) Å, c= (3) Å, Reliability factors : Rp= 25.1, Rwp = 18.6, Bragg-R = 8.43, Chi^2 = 1.78 Ti1 4a 0.000 0.5 1.2(2) Ti2 4b 0.500 Ti3 4c 0.016(12) 0.25 0.252(6) 0.34(5) O1 0.239(5) 0.269(2) 1.3(1) F1 8d 0.248(3) -0.022(3) 0.480(1) 1.0 O2 -0.026(4) 0.976(2) F2 0.043(2) 0.068(3) 0.143(2) O3 0.536(4) -0.046(3) F3 0.012(3) -0.062(3) 0.646(2) O4 0.267(8) 0.744(3) 0.41(6) 2.8(9) H1 0.341(17) 0.158(15) 0.744(9) H2 0.628(9) 0.825(6)
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Structural features of (Ti0.9M0.1)1-(O,OH,F)3 HTB-Pnma
(M=V, Mo, W) atomic positions and bond distances Distances (Å) X-ray at T=293K Ti1 → F1 1.87(6) Ti1 → F2 1.99(5) Ti1 → O2 1.92(2) Ti2 → F1 1.93(7) Ti2 → O3 2.13(3) Ti2 → F3 2.01(6) Ti2 → H2 3.06(1) Ti3 → O1 1.87(13)/1.92(13) Ti3 → F2 1.82(5) Ti3 → F3 1.82(6) Ti3 → H1 3.24(2) O1 → F2 2.58(13)/2.67(13) O1 → F3 2.71(13)/2.56(13) O1 → H1 3.10(4) F1 → F2 2.73(8)/2.74(9) F1 → O2 2.68(9)/2.68(9) F1 → O3 2.89(9)/2.86(9) F1 → F3 2.74(8)/2.83(9) F2 → O2 2.71(8)/2.82(8) F2 → F3 2.62(8) F2 → O4 3.21(6) F2 → H1 2.38(5) O2 → H1 2.92(7) O3 → O4 3.01(9)/2.80(9) O3 → H1 2.70(7) O3 → H2 1.44(7) F3 → H1 3.17(6)/2.63(6) F3 → H2 2.55(5) O4 → H1 1.22(4) O4 → H2 1.37(5) H1 → H2 1.96(5) Distances (Å) M = V M = Mo M = W Ti1/M1 → F1 1.76(1) 1.87(1) 1.79(1) Ti1/M1 → F2 2.09(2) 1.92(1) Ti1/M1 → O2 1.931(6) 1.901(6) 1.875(4) Ti2/M2 → F1 2.04(1) 1.95(1) 2.03(1) Ti2/M2 → O3 1.907(5) 2.030(7) 2.255(8) Ti2/M2 → F3 1.94(1) 2.05(1) 1.939(2) Ti2/M2 → H2 3.060(1) 3.058(1) 3.053(1) Ti3/M3 → O1 1.81(1)/1.97(1) 1.75(2)/2.03(2) 1.86(4)/1.95(4) Ti3/M3 → F2 1.78(1) 1.89(2) Ti3/M3 → F3 1.91(1) 1.82(1) 1.86(1) O1 → F2 2.53(1)/2.69(1) 2.66(2)/2.71(2) 2.58(3)/2.84(3) O1 → F3 2.82(1)/2.50(2) 2.71(2)/2.48(2) 2.80(3)/2.52(3) O1 → H1 3.088(3) 3.092(5) 3.093(8) F1 → F2 2.64(1)/2.83(1) 2.61(1)/2.74(2) 2.51(1)/2.74(1) F1 → O2 2.54(1)/2.68(1) 2.76(2)/2.56(2) 2.72(2)/2.46(2) F1 → O3 2.77(1)/2.82(1) 2.90(2)/2.74(2) 3.08(2)/2.98(2) F1 → F3 2.87(1)/2.77(1) 2.89(1)/2.77(2) 2.85(2)/2.76(2) F2 → O2 2.75(1)/2.75(1) 2.67(3)/2.73(2) 2.55(2)/2.81(1) F2 → F3 2.53(2) 2.62(2) 2.69(3) F2 → O4 3.06(1) 3.26(1) 3.06(2) F2 → H1 2.27(1) 2.37(1) 2.30(1) O2 → H1 2.88(1) 2.97(2) 3.08(2) O3 → O4 3.34(2)/3.38(2) 3.04(3)/3.03(1) 2.73(3)/2.65(3) O3 → H1 3.20(2) 2.86(2) 2.55(2)/3.04(1) O3 → H2 1.96(2) 1.62(2) 1.19(2) F3 → H1 3.20(1)/2.65(1) 3.14(1)/2.65(1) 2.50(2) F3 → H2 2.55(1) 2.56(2) 2.57(1) O4 → H1 1.15(1) 1.02(2) 0.840(9) O4 → H2 3.13(1)/1.39(1) 3.01(2)/1.41(1) 2.82(2)/1.43(3) H1 → H2 2.49/1.96 2.492/1.960 2.489/1.958
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