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Technetium Bromides as Precursors for the Synthesis of Low-Valent Complexes

Technetium Bromides as Precursors for the Synthesis of Low-Valent Complexes. F. Poineau 1 , A. P. Sattelberger 2 , P. Weck 1 , P. Forster 1 , L. Gagliardi 3 , K. R. Czerwinski 1. Department of Chemistry, University of Nevada Las Vegas, Las Vegas, USA

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Technetium Bromides as Precursors for the Synthesis of Low-Valent Complexes

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  1. Technetium Bromides as Precursors for the Synthesis of Low-Valent Complexes F. Poineau1, A. P. Sattelberger2, P. Weck1,P. Forster1, L. Gagliardi3, K. R. Czerwinski1 • Department of Chemistry, University of Nevada Las Vegas, Las Vegas, USA • Energy Sciences and Engineering Directorate, ANL, Argonne, USA • Department of Chemistry, University of Minnesota, Minneapolis, USA

  2. Harry Reid Center, University of Nevada Las VegasFocus on fundamental and applied research on Technetium Synthetic and coordination chemistry of 99Tc -Metal-metal bonded compounds, Binary halides, and Oxides. Structure of Bi2Tc2O7 Chemistry relevant to the nuclear fuel cycle - Separation and waste forms Capabilities Synthesis: Ability to work with high activity: (mg to g of 99Tc) glove box, Schlenk line,HEPA-filtered fume hoods Characterization: Spectroscopy: UV-Vis, IR, NMR, TRFLS & XAFS Diffraction: XRD (single crystal and powder) & NPD First principles calculations U/Tc separation Tc laboratory at UNLV

  3. Fundamental Chemistry of Tc • Metal-metal bonded dimers •  Five quadruple bonded dimers are characterized: (n-Bu4N)2Tc2Cl8, • Tc2(O2CCMe3)4Cl2, Tc2(O2CMe3)4(TcO4)2, K2Tc2(SO4)4·2H2O, Tc2(O2CMe3)2Cl2(dma)2. •  No bromides characterized • 2. Binary Halides •  Three compounds known : TcCl4, TcF5 and TcF6 •  No binary iodides and bromides characterized • Synthesis & characterization of Tc binary bromides and metal-metal bonded dimers • Use as precursor for synthesis of new complexes

  4. I - Synthesis and characterization of binary bromides II - Synthesis and characterization of (n-Bu4N)2Tc2Br8 III - Reaction : TcBr3 and PMe3\NaEt3BH IV - Reaction : (n-Bu4N)2Tc2Br8 and PMe3

  5. I. Synthesis of binary bromides Binary halides of transition metals:  reaction of the metal and halogen at elevated temperature Ex: M + (3/2) Br2→ MBr3 (M = Ru, Re, Mo); M + 3F2→ MF6 ( M = Tc, Ru, Mo) 1. Synthesis of Tc metal T = 700 ºC T = 750 ºC Ar/H2 Ar NH4TcO4 TcO2 Tc metal 2. Reaction between Tc metal and Br2 and I2 in sealed tube T = 400 ºC 6 hours Glass blowing • Iodine: No reaction • Bromine: Formation of dark crystalline compound

  6. Analysis by single crystal XRD For Tc:Br ~ 1:4 → Formation of TcBr4* *Poineau, F et al. JACS, 2009 - Infinite chains of edge-sharing TcBr6 octahedra - First binary tetrabromide of group VII characterized - Isostructural to MBr4 (M = Pt, Os) and TcCl4. Distance (Å) in TcBr4 Large d(Tc-Tc) no metal-metal bond Br(1) Br(3) Tc Br(2)

  7. For Tc:Br ~ 1:3→ Formation of TcBr3 - Infinite chains of face-sharing TcBr6 octahedra - First d4 binary halide with this structure - Isostructural to MBr3 (M = Mo, Ru) - (!) ReBr3: Chain of “Re3Br9” units Distance (Å) in TcBr3 Alternation short /long d(Tc-Tc)  deformation of “TcBr6” octahedra Br(A) Br(B) Tc1 Tc2 Tc3

  8. First principles calculations on Tc tetrahalides Prediction of TcF4*, Isostructural to TcX4 (X = Cl, Br) *Weck, P. et al. Inorg. Chem. 2009 X1 X3 X2 Distance (Å) in TcX4 Synthesis: Thermal decomposition of H2TcF6

  9. II. Synthesis of (n-Bu4N)2Tc2Br8 12 M HCl (n-Bu4N)TcO4 T = 80 °C, H2O2 (n-Bu4N)OH T = 0 °C TcO2/NH4TcO4 (n-Bu4N)TcOCl4 (n-Bu4N)BH4 THF & HBr gas HCl, acetone T = 30 °C (n-Bu4N)2Tc2Br8 (n-Bu4N)2Tc2Cl8

  10. Recrystallization from acetone / ether for single crystal XRD  Formation of an acetone solvate: (n-Bu4N)2Tc2Br8. 4[(CH3)2CO]* * Poineau , F et al. Dalton. Trans. 2009 View of the solvate from the a direction Tc2Br82- ion Steric effect induced by bromide in [Tc2Br8]2- ion:  Increase of Tc-Tc separation and the Tc-Tc-Br angle

  11. III. Reaction: TcBr3 and PMe3/NaEt3BH Binary halides as precursors of low valent complexes Ex: Compounds of the type MX2(PMe3)4 (X = Cl, Br) - Metal halide reduction by Na /Hg in presence of excess PMe3 Technetium tribromide: reaction in THF with 30 mol xs PMe3 and 1.3 eq. NaEt3BH 1. Stirring 12 hours under Ar 2. Pumping todryness 3. Extraction and crystallization from hexane TcBr3 Tc2Br4(PMe3)4 TcBr2(PMe3)4

  12. Structure A) Tc2Br4(PMe3)4 C P - First Tc2IIBr4(PR3)4 characterized - Triple Tc-Tc bonded dimer: s2p4d2d*2 - Isomorphous to M2Br4(PMe3)4 (M = Re, Mo) - Tc2Cl4(PR3)4 know and characterized Zinc reduction of TcIVCl4(PR3)2 in THF Br Tc Moving from Tc to Re: Increase of metal-metal separation.  Decrease of M-M-Br and M-M-P angles and of the M-Br and M-P distances

  13. B) TcBr2(PMe3)4 • - First MIIX2(PMe3)4 for group VII • Isomorphous to MoBr2(PMe3)4 • Octahedral complex: • Four equatorial PMe3, trans-axial Br. Comparison monomer/dimer: d(Tc-Br) monomer > d(Tc-Br) dimer d(Tc-P) dimer > d(Tc-P) monomer Similar phenomena for molybdenum Elongation of Tc-Br distance due to steric effect of 4 equatorial PMe3 Elongation of Tc-P in dimer due to steric interaction Br-Me.

  14. UV-Visible spectroscopy A) Tc2Br4(PMe3)4 in benzene Attribution of transition based on Time Dependant/DFT calculations

  15. B) TcBr2(PMe3)4 in dichloromethane

  16. IV. Reaction : (n-Bu4N)2Tc2Br8 and PMe3 Metal-metal bonded precursor of low-valent complexes Ex: (n-Bu4N)2Re2Cl8 precursor to Re2Cl8-x(PMe3)x, (x = 2, 3, 4) • Expected :(n-Bu4N)2Tc2Br8 + xPMe3 Tc2Br8-x(PMe3)x+ x(n-Bu4N)Br (n-Bu4N)Tc2Br8: reaction in CH2Cl2 with 30 mol xs PMe3 1. Five minutes under Ar 2. Pumping todryness 3. Extraction and Recrystallization In hexane XRD : Tc2Br4(PMe3)4

  17. Electrochemistry Cyclic Voltammetry in CH2Cl2/0.1 M (n-Bu4N)BF4 Working electrode: Pt disk. Ref.: Ag wire. Scan rate = 200mV.s-1; FeCp2 standard. 1. Rhenium complex more readily oxidized than technetium 2. Formation of Tc2Br4(PMe3)4+ and Tc2Br4(PMe3)42+ core  Chemical or electrochemical synthesis of Tc2Br5(PMe3)3 and Tc2Br6(PMe3)2

  18. Conclusion • Synthesis and characterization of TcBr3 and TcBr4 • - First Tc binary bromides. • Structural characterization (n-Bu4N)2Tc2Br8.4[(CH3)2CO] • - Influence of X on Tc-Tc separation in Tc2X8 • Reaction of TcBr3 with PMe3/NaEt3BH  Two new complexes •  TcBr2(PMe3)4: First MX2(PMe3)4compound of Group VII • Tc2Br4(PMe3)4 :Also synthesized from (n-Bu4N)2Tc2Br8/ PMe3 First Tc2X4(PR3)4 bromide • Structural and spectroscopic studies of TcBr2(PMe3)4 & Tc2Br4(PMe3)4 • - Influence of local geometry on metal-ligand separation. • - Attribution of electronic transitions in UV-Vis spectra.

  19. Perspectives • Search for Tc binary halides • TcCl3: Thermal decomposition of Tc2(OCCH3)4Cl2 under HCl • TcF4: Thermal decomposition of H2TcF6 under Ar • New reactions using TcBr3 as precursor • Conversion of TcBr3 to (n-Bu4N)2Tc2Br8 • Optimize the synthesis of TcBr2(PMe3)4 and Tc2Br4(PMe3)4 • TcBr2(PMe3)4: Precursor for TcBr2(H2)(PMe3)4 and TcBr2(C2H4)(PMe3)4 • Tc2Br4(PMe3)4: Precursor for Tc2Br6(PMe3)2

  20. Acknowledgments Tom O’Dou Health Physics Radiochemistry program at UNLV

  21. Questions

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