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