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 1.Department of Chemistry, University of Nevada Las Vegas, Las Vegas, USA 2.Energy Sciences and Engineering Directorate, ANL, Argonne, USA 3.Department of Chemistry, University of Minnesota, Minneapolis, USA

Harry Reid Center, University of Nevada Las Vegas Focus on fundamental and applied research on Technetium Synthesis: Ability to work with high activity: (mg to g of 99 Tc) 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 Synthetic and coordination chemistry of 99 Tc -Metal-metal bonded compounds, Binary halides, and Oxides. Tc laboratory at UNLV U/Tc separation Chemistry relevant to the nuclear fuel cycle - Separation and waste forms Structure of Bi 2 Tc 2 O 7 Capabilities

Fundamental Chemistry of Tc 1.Metal-metal bonded dimers  Five quadruple bonded dimers are characterized: (n-Bu 4 N) 2 Tc 2 Cl 8, Tc 2 (O 2 CCMe 3 ) 4 Cl 2, Tc 2 (O 2 CMe 3 ) 4 (TcO 4 ) 2, K 2 Tc 2 (SO 4 ) 4 ·2H 2 O, Tc 2 (O 2 CMe 3 ) 2 Cl 2 (dma) 2.  No bromides characterized 2. Binary Halides  Three compounds known : TcCl 4, TcF 5 and TcF 6  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

I - Synthesis and characterization of binary bromides II - Synthesis and characterization of (n-Bu 4 N) 2 Tc 2 Br 8 III - Reaction : TcBr 3 and PMe 3 \NaEt 3 BH IV - Reaction : (n-Bu 4 N) 2 Tc 2 Br 8 and PMe 3

Binary halides of transition metals:  reaction of the metal and halogen at elevated temperature Ex: M + (3/2) Br 2 → MBr 3 (M = Ru, Re, Mo); M + 3F 2 → MF 6 ( M = Tc, Ru, Mo) 1. Synthesis of Tc metal TcO 2 NH 4 TcO 4 T = 750 ºC Ar I. Synthesis of binary bromides 2. Reaction between Tc metal and Br 2 and I 2 in sealed tube 6 hours  Iodine: No reaction  Bromine: Formation of dark crystalline compound T = 700 ºC Ar/H 2 T = 400 ºC Tc metal Glass blowing

Analysis by single crystal XRD - Infinite chains of edge-sharing TcBr 6 octahedra - First binary tetrabromide of group VII characterized - Isostructural to MBr 4 (M = Pt, Os) and TcCl 4. Br(1) Br(2) Tc Br(3) d(Tc-Tc)3.791d(Tc-Br(3))2.525 d(Tc-Br(1))2.395d(Tc-Br(2))2.623 For Tc:Br ~ 1:4 → Formation of TcBr 4 * Distance (Å) in TcBr 4 Large d(Tc-Tc)  no metal-metal bond *Poineau, F et al. JACS, 2009

For Tc:Br ~ 1:3→ Formation of TcBr 3 - Infinite chains of face-sharing TcBr 6 octahedra - First d 4 binary halide with this structure - Isostructural to MBr 3 (M = Mo, Ru) - (!) ReBr 3 : Chain of “Re 3 Br 9 ” units d(Tc1-Tc2)3.060d(Tc1-Br(A))2.489 d(Tc2-Tc1)2.915d(Tc2-Br(B))2.523 Distance (Å) in TcBr 3 Tc2 Tc1 Tc3 Br(A)Br(B) Alternation short /long d(Tc-Tc)  deformation of “TcBr 6 ” octahedra

First principles calculations on Tc tetrahalides Prediction of TcF 4 *, Isostructural to TcX 4 (X = Cl, Br) Synthesis: Thermal decomposition of H 2 TcF 6 TcCl 4 TcBr 4 TcF 4 ExpDFTExpDFT Tc-Tc Tc-X Tc-X Tc-X X1 X2 X3 *Weck, P. et al. Inorg. Chem Distance (Å) in TcX 4

II. Synthesis of (n-Bu 4 N) 2 Tc 2 Br 8 (n-Bu 4 N)TcO 4 (n-Bu 4 N)TcOCl 4 (n-Bu 4 N) 2 Tc 2 Cl 8 (n-Bu 4 N) 2 Tc 2 Br 8 TcO 2 /NH 4 TcO 4 T = 80 °C, H 2 O 2 (n-Bu 4 N)OH 12 M HCl T = 0 °C (n-Bu 4 N)BH 4 THF HCl, acetone HBr gas T = 30 °C &

CompoundsTc-Tc (Å) (Å) (°) (n-Bu 4 N) 2 Tc 2 Br 8 ·4[(CH 3 ) 2 CO]2.1625(9)2.4734(7)105.01(3) (n-Bu 4 N) 2 Tc 2 Cl (4)2.320(4)103.8(4) Recrystallization from acetone / ether for single crystal XRD  Formation of an acetone solvate: (n-Bu 4 N) 2 Tc 2 Br 8. 4[(CH 3 ) 2 CO]* Tc 2 Br 8 2- ion Steric effect induced by bromide in [Tc 2 Br 8 ] 2- ion:  Increase of Tc-Tc separation and the Tc-Tc-Br angle View of the solvate from the a direction * Poineau, F et al. Dalton. Trans. 2009

Binary halides as precursors of low valent complexes Ex: Compounds of the type MX 2 (PMe 3 ) 4 (X = Cl, Br) III. Reaction: TcBr 3 and PMe 3 /NaEt 3 BH Nb NbCl 5 Mo MoCl 3 (THF) 3 Tc ? Ru RuCl 3 Ta TaCl 5 W WCl 4 Re ? Os (NH 4 ) 2 OsCl 6 - Metal halide reduction by Na /Hg in presence of excess PMe 3 TcBr 2 (PMe 3 ) 4 TcBr 3 Tc 2 Br 4 (PMe 3 ) 4 Technetium tribromide: reaction in THF with 30 mol xs PMe 3 and 1.3 eq. NaEt 3 BH 2. Pumping to dryness 3. Extraction and crystallization from hexane 1. Stirring 12 hours under Ar

Structure M 2 Br 4 (PMe 3 ) 4 Average distancesAverage angles M-MM-BrM-PM-M-BrM-M-P Tc 2 Br 4 (PMe 3 ) (5)2.520(1)2.441(1)114.35(1)102.33(2) Re 2 Br 4 (PMe 3 ) (3)2.5034(5)2.4201(11)113.98(1)101.05(3) A) Tc 2 Br 4 (PMe 3 ) 4 - First Tc 2 II Br 4 (PR 3 ) 4 characterized - Triple Tc-Tc bonded dimer:  2  4  2  * 2 - Isomorphous to M 2 Br 4 (PMe 3 ) 4 (M = Re, Mo) - Tc 2 Cl 4 (PR 3 ) 4 know and characterized Zinc reduction of Tc IV Cl 4 (PR 3 ) 2 in THF Tc Br C P 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

B) TcBr 2 (PMe 3 ) 4 - First M II X 2 (PMe 3 ) 4 for group VII - Isomorphous to MoBr 2 (PMe 3 ) 4 - Octahedral complex: Four equatorial PMe 3, trans-axial Br. TcMo d(Tc-Br)d(Tc-P)d(Mo-Br)d(Mo-P) MBr 2 (PMe 3 ) (7)2.4214(11)2.614(1)2.515(1) M 2 Br 4 (PMe 3 ) (1)2.441(1)2.549(1)2.547(2) d(Tc-Br) monomer > d(Tc-Br) dimer d(Tc-P) dimer > d(Tc-P) monomer Similar phenomena for molybdenum Comparison monomer/dimer: Elongation of Tc-Br distance due to steric effect of 4 equatorial PMe 3 Elongation of Tc-P in dimer due to steric interaction Br-Me.

UV-Visible spectroscopy A) Tc 2 Br 4 (PMe 3 ) 4 in benzene Attribution of transition based on Time Dependant/DFT calculations

B) TcBr 2 (PMe 3 ) 4 in dichloromethane

3. Extraction and Recrystallization In hexane XRD : Tc 2 Br 4 (PMe 3 ) 4 IV. Reaction : (n-Bu 4 N) 2 Tc 2 Br 8 and PMe 3  Expected : (n-Bu 4 N) 2 Tc 2 Br 8 + xPMe 3  Tc 2 Br 8-x (PMe 3 ) x + x(n-Bu 4 N)Br Metal-metal bonded precursor of low-valent complexes Ex: (n-Bu 4 N) 2 Re 2 Cl 8 precursor to Re 2 Cl 8-x (PMe 3 ) x, (x = 2, 3, 4) 1. Five minutes under Ar 2. Pumping to dryness (n-Bu 4 N)Tc 2 Br 8 : reaction in CH 2 Cl 2 with 30 mol xs PMe 3

Cyclic Voltammetry in CH 2 Cl 2 /0.1 M (n-Bu 4 N)BF 4 1. Rhenium complex more readily oxidized than technetium 2. Formation of Tc 2 Br 4 (PMe 3 ) 4 + and Tc 2 Br 4 (PMe 3 ) 4 2+ core  Chemical or electrochemical synthesis of Tc 2 Br 5 (PMe 3 ) 3 and Tc 2 Br 6 (PMe 3 ) 2 Electrochemistry Working electrode: Pt disk. Ref.: Ag wire. Scan rate = 200mV.s -1 ; FeCp 2 standard.

Conclusion Synthesis and characterization of TcBr 3 and TcBr 4 - First Tc binary bromides. Structural characterization (n-Bu 4 N) 2 Tc 2 Br 8.4[(CH 3 ) 2 CO] - Influence of X on Tc-Tc separation in Tc 2 X 8 Reaction of TcBr 3 with PMe 3 /NaEt 3 BH  Two new complexes  TcBr 2 (PMe 3 ) 4 : First MX 2 (PMe 3 ) 4 compound of Group VII  Tc 2 Br 4 (PMe 3 ) 4 : Also synthesized from (n-Bu 4 N) 2 Tc 2 Br 8 / PMe 3 First Tc 2 X 4 (PR 3 ) 4 bromide Structural and spectroscopic studies of TcBr 2 (PMe 3 ) 4 & Tc 2 Br 4 (PMe 3 ) 4 - Influence of local geometry on metal-ligand separation. - Attribution of electronic transitions in UV-Vis spectra.

Perspectives Search for Tc binary halides - TcCl 3 : Thermal decomposition of Tc 2 (OCCH 3 ) 4 Cl 2 under HCl - TcF 4 : Thermal decomposition of H 2 TcF 6 under Ar New reactions using TcBr 3 as precursor - Conversion of TcBr 3 to (n-Bu 4 N) 2 Tc 2 Br 8 Optimize the synthesis of TcBr 2 (PMe 3 ) 4 and Tc 2 Br 4 (PMe 3 ) 4 - TcBr 2 (PMe 3 ) 4 : Precursor for TcBr 2 (H 2 )(PMe 3 ) 4 and TcBr 2 (C 2 H 4 )(PMe 3 ) 4 - Tc 2 Br 4 (PMe 3 ) 4 : Precursor for Tc 2 Br 6 (PMe 3 ) 2

Acknowledgments Tom O’Dou Health Physics Radiochemistry program at UNLV

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