technetium bromides as precursors for the synthesis of low-valent complexes f. poineau 1, a. p....
TRANSCRIPT
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
1. Department of Chemistry, University of Nevada Las Vegas, Las Vegas, USA 2. Energy Sciences and Engineering Directorate, ANL, Argonne, USA3. 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 99Tc)glove box, Schlenk line, HEPA-filtered fume hoodsCharacterization:Spectroscopy: UV-Vis, IR, NMR, TRFLS & XAFSDiffraction: XRD (single crystal and powder) & NPDFirst principles calculations
Synthetic and coordination chemistry of 99Tc-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 Bi2Tc2O7
Capabilities
Fundamental Chemistry of Tc
1. 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
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
Binary halides of transition metals: reaction of the metal and halogen at elevated temperatureEx: M + (3/2) Br2→ MBr3 (M = Ru, Re, Mo); M + 3F2→ MF6 ( M = Tc, Ru, Mo)
1. Synthesis of Tc metal
TcO2NH4TcO4
T = 750 ºC
Ar
I. Synthesis of binary bromides
2. Reaction between Tc metal and Br2 and I2 in sealed tube
6 hours
Iodine: No reactionBromine: Formation of dark crystalline compound
T = 700 ºC
Ar/H2
T = 400 ºC
Tc metal
Glass blowing
Analysis by single crystal XRD
- Infinite chains of edge-sharing TcBr6 octahedra- First binary tetrabromide of group VII characterized- Isostructural to MBr4 (M = Pt, Os) and TcCl4.
3.791 ÅBr(1)
Br(2)
TcBr(3)
d(Tc-Tc) 3.791 d(Tc-Br(3)) 2.525
d(Tc-Br(1)) 2.395 d(Tc-Br(2)) 2.623
For Tc:Br ~ 1:4 → Formation of TcBr4*
Distance (Å) in TcBr4
Large d(Tc-Tc) no metal-metal bond
*Poineau, F et al. JACS, 2009
3.060 Å 2.915 Å
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
d(Tc1-Tc2) 3.060 d(Tc1-Br(A)) 2.489
d(Tc2-Tc1) 2.915 d(Tc2-Br(B)) 2.523
Distance (Å) in TcBr3
Tc2Tc1 Tc3
Br(A) Br(B)
Alternation short /long d(Tc-Tc) deformation of “TcBr6” octahedra
First principles calculations on Tc tetrahalides
Prediction of TcF4*, Isostructural to TcX4 (X = Cl, Br)
Synthesis: Thermal decomposition of H2TcF6
TcCl4 TcBr4 TcF4
Exp DFT Exp DFT DFT
Tc-Tc 3.62 3.77 3.94 3.79 3.32
Tc-X1 2.25 2.26 2.395 2.41 1.87
Tc-X2 2.38 2.38 2.525 2.52 2.02
Tc-X3 2.49 2.45 2.62 2.61 2.05
X1
X2
X3*Weck, P. et al. Inorg. Chem. 2009
Distance (Å) in TcX4
II. Synthesis of (n-Bu4N)2Tc2Br8
(n-Bu4N)TcO4 (n-Bu4N)TcOCl4
(n-Bu4N)2Tc2Cl8 (n-Bu4N)2Tc2Br8
TcO2/NH4TcO4
T = 80 °C, H2O2
(n-Bu4N)OH
12 M HCl
T = 0 °C
(n-Bu4N)BH4
THF
HCl, acetone
HBr gas
T = 30 °C
&
Compounds Tc-Tc (Å) <Tc-X> (Å) <Tc-Tc-X> (°)
(n-Bu4N)2Tc2Br8·4[(CH3)2CO] 2.1625(9) 2.4734(7) 105.01(3)
(n-Bu4N)2Tc2Cl8 2.147(4) 2.320(4) 103.8(4)
Recrystallization from acetone / ether for single crystal XRD Formation of an acetone solvate: (n-Bu4N)2Tc2Br8. 4[(CH3)2CO]*
Tc2Br82- ion
Steric effect induced by bromide in [Tc2Br8]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 complexesEx: Compounds of the type MX2(PMe3)4 (X = Cl, Br)
III. Reaction: TcBr3 and PMe3/NaEt3BH
Nb
NbCl5
Mo
MoCl3(THF)3
Tc
?
Ru
RuCl3
Ta
TaCl5
W
WCl4
Re
?
Os
(NH4)2OsCl6
- Metal halide reduction by Na /Hg in presence of excess PMe3
TcBr2(PMe3)4TcBr3 Tc2Br4(PMe3)4
Technetium tribromide: reaction in THF with 30 mol xs PMe3 and 1.3 eq. NaEt3BH
2. Pumping to dryness3. Extraction and crystallization from hexane
1. Stirring 12 hours under Ar
Structure
M2Br4(PMe3)4 Average distances Average angles
M-M M-Br M-P M-M-Br M-M-P
Tc2Br4(PMe3)4 2.1316(5) 2.520(1) 2.441(1) 114.35(1) 102.33(2)
Re2Br4(PMe3)4 2.2521(3) 2.5034(5) 2.4201(11) 113.98(1) 101.05(3)
A) Tc2Br4(PMe3)4
- First Tc2IIBr4(PR3)4 characterized
- Triple Tc-Tc bonded dimer: 242*2
- Isomorphous to M2Br4(PMe3)4 (M = Re, Mo)
- Tc2Cl4(PR3)4 know and characterized Zinc reduction of TcIVCl4(PR3)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
Tc
Br
P
C1
C2
B) TcBr2(PMe3)4
- First MIIX2(PMe3)4 for group VII - Isomorphous to MoBr2(PMe3)4
- Octahedral complex: Four equatorial PMe3, trans-axial Br.
Tc Mo
d(Tc-Br) d(Tc-P) d(Mo-Br) d(Mo-P)
MBr2(PMe3)4 2.5925(7) 2.4214(11) 2.614(1) 2.515(1)
M2Br4(PMe3)4 2.520(1) 2.441(1) 2.549(1) 2.547(2)
d(Tc-Br) monomer > d(Tc-Br) dimerd(Tc-P) dimer > d(Tc-P) monomerSimilar phenomena for molybdenum
Comparison monomer/dimer:
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.
UV-Visible spectroscopy
A) Tc2Br4(PMe3)4 in benzene
0
100
10 20 30Wavenumber / 10 3 cm -1Wavenumber / 10 3 cm -1
e m
ol-1
.cm
-1
*" **" *
Attribution of transition based on Time Dependant/DFT calculations
0
3000
290 390 490 590 690
e (m
ol-1
.cm
-1)
Wavelength (nm)
LMCT
1e
e-
3e
LMCT
2e
e-
3e
B) TcBr2(PMe3)4 in dichloromethane
3. Extraction and Recrystallization
In hexane
XRD : Tc2Br4(PMe3)4
IV. Reaction : (n-Bu4N)2Tc2Br8 and PMe3
Expected : (n-Bu4N)2Tc2Br8 + xPMe3 Tc2Br8-x(PMe3)x + x(n-Bu4N)Br
Metal-metal bonded precursor of low-valent complexesEx: (n-Bu4N)2Re2Cl8 precursor to Re2Cl8-x(PMe3)x, (x = 2, 3, 4)
1. Five minutes under Ar2. Pumping to dryness
(n-Bu4N)Tc2Br8: reaction in CH2Cl2 with 30 mol xs PMe3
-50
150
-2 -1 0 1 2
M(II)-M(III) → M(III)-M(III)
40 µ
A
M(II)-M(II) → M(II)-M(III)
Volts vs. Cp2Fe/ Cp2Fe+
Cu
rren
t
Tc2Br4(PMe3)4
Re2Br4(PMe3)4
Cyclic Voltammetry in CH2Cl2/0.1 M (n-Bu4N)BF4
1. Rhenium complex more readily oxidized than technetium2. Formation of Tc2Br4(PMe3)4
+ and Tc2Br4(PMe3)42+ core
Chemical or electrochemical synthesis of Tc2Br5(PMe3)3 and Tc2Br6(PMe3)2
Electrochemistry
Working electrode: Pt disk. Ref.: Ag wire. Scan rate = 200mV.s-1; FeCp2 standard.
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)4 compound 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.
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
Acknowledgments
Tom O’DouHealth Physics
Radiochemistry program at UNLV
Questions