Introduction to

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Introduction to Technetium Chemistry
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Technetium Group VII second row transition
metal Lightest radioactive element (no stable
isotopes)
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Historic

• 1869 Predicted by D. Mendeleev

• 1934 Predicted to have no stable isotope
  (Mattauch rule)

• 1937 Discovered by E. Segre and C. Perrier

Irradiation of molybdenum plate at Berkeley
cyclotron
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Lightest radioactive element (no stable isotopes)
Why there are no stable isotopes ?

• If there was stable isotope they should
• located in the valley of stability in the
  chart
• of the nuclides
• ? 97Tc, 98Tc, 99Tc, 100Tc, 101Tc

2. These isotopes should have the lowest binding
energy (Eb) among element with same Z
Eb Energy required to dissociate the nucleus
into its constituent nucleons
Eb ZMH (A-Z)MN M Nucleus
A 42Mo 43Tc 44Ru
97 -87.54 -87.22 -86.11
98 -88.11 -86.43 -88.22
99 -85.97 -87.32 -87.62
100 -86.18 -86.02 -89.22
101 -83.51 -86.34 -87.95
For Z 97 to 101 Technetium isotopes do not
have the lowest Eb
Table of binding energy Most stable isotopes are
in red
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Isotopes

• 32 isotopes from 85Tc to 115Tc
• 115Tc T1/2 130 ms (shortest)
• 98Tc T1/2 4.6.106 y (longest)
• Two isotopes of interest
• 99Tc (Fission product of nuclear industry)
• T1\2 2.13. 105 year, b- 294 keV
• Specific activity 0.63 Giga-Becquerel by gram
• 99mTc (Imaging agent in nuclear medicine)
• T1/2 6.02 h, g 141 keV
• 194000 Tera-Becquerel by gram

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Production

• 99mTc produced from the decay of 99Mo
• 99Mo produced by fission of 235U

Fission of 235U
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99Tc Fission product of nuclear industry yield
6 from fission of 235U ? 0.8 kg/ MT of spent
fuel Each year, 2 tons of 99Tc are produced by
US nuclear industry
e-phase Micron-sized particles
In spent fuel Tc is present as metal or alloys
with Mo-Ru-Pd Rh (e-phase)
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Applications

• 99mTc Imaging agent in nuclear medicine 90 of
  all radiodiagnostic tests
• Optimal nuclear properties Energy allows
  imaging deep organs without damage
• Versatile chemistry Coordination with suitable
  functional group (brain, heart, bone,..)

Cardiolite Heart imaging , 40 million
patients treated since 1991
Cardiolite Tc(CNCH2C(Me)2OMe)6
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Potential applications
Catalyst Tc efficient catalytic properties for
Aldehyde production Anti-corrosive agent 55
ppm in steel avoid corrosion (Passivation by
insoluble Tc oxide). Electronic compounds Tc
metal is super-conductor at 7.46 K. Source of
ruthenium Transmutation of 99Tc to 100Ru
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Transmutation

• Transmutation of 99Tc by neutron capture
• 99Tc n ? 100Tc ? 100Ru (Stable) b-
• Exp. demonstration performed in 2003- 2008 in a
  fast neutron reactor

Transmuted Tc Tc/Ru alloys
Assembly for transmutation
Fast neutron reactor, France

• 5 years irradiation 25 of Tc transmuted into
  Ru

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Tc in Environment

• 99Tc in environment as the TcO4- anion
• 1. Nuclear fuel reprocessing
• 3 tons rejected in the Sea (since 1984)
• - Sellafield (U.K) 140 kg by year
• - La Hague (France) 1.6 kg by year
• 2. Atomic Weapons Tests 390 470 kg
• 3. Chernobyl Explosion 2 kg
• 4. Nuclear Medicine (Low)

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Understand fundamental chemistry of technetium

• Improve nuclear fuel cycle applications
• Development of new imaging agents
• Predict Tc behavior in environment

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Inorganic Chemistry
1. Characteristic 2. Solid-state compounds 3.
Complexes with multiple metal-metal bonds 4.
Aqueous chemistry 5. Summary
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1. Characteristic
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Characteristic Tc Re
Atomic Number 43 75
M 98 186.20
Electronic Structure Kr4d55s2 Xe4f145d56s2

• Tc and Re share similar electronic structure
• Similar coordination complexes

Binary halides
Metal-metal bonded dimers
Heptavalent complexes
MF5
MO4-
M2Cl82-

• Tc coordination chemistry less developed than Re
  (as of 2008)

Binary halides Metal-metal bonded dimers Heptavalent complexes
Tc 3 25 30
Re 15 500 150

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9 oxidations state from 7 to -1
tetrahedral
Ox. state Tc config. Compound
7 Kr4d0 KTcO4
6 Kr4d1 (TBA)TcNCl4
5 Kr4d2 (TBA)TcOCl4
4 Kr4d3 K2TcCl6
3 Kr4d4 (TBA)3Tc(NCS)6
2 Kr4d5 TcCl2(PMe3)4
1 Kr4d6 K5Tc(CN)6
0 Kr4d7 Tc2(CO)10
-1 Kr4d8 Tc(CO)5-
TcO4-
octahedral
TcL6 anion L Cl, NCS, CN
Square pyramidal
TBA Tetrabutyl-ammonium, (Bu4N)
TcLCl4 anion L N, O
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2. Solid-state compounds A. Metal B. Binary
oxides C. Binary halides D. Other binary compounds
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A. Metal

• Structure Hexagonal (Hcp)
• Density 11.49
• Melting point 2200 C
• Boiling point 4270 C
• Synthesis
• ? Thermal reduction of NH4TcO4 under H2 at T gt
  500 C
• NH4TcO4 2H2 ? Tc 4H2O (1/2)N2
• ? Electro-reduction of TcO4- in H2SO4

Hcp structure
Tc metal on Cu electrode
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B. Binary Oxides
Transition metal binary oxides MOn (n 1- 4) 70
are known (e.g., 5 for Mn, 3 for Re) 2 technetium
binary oxides
Ox. state Solid Characteristic
7 Tc2O7 Molecular dimer
4 TcO2 Extended structure Isostructural to ReO2
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1. TcO2
Decomposition of NH4TcO4 under Ar atmosphere at
750 C NH4TcO4 ? TcO2 2H2O (1/2)N2
T 750 ºC
Ar
TcO2
NH4TcO4
Set-up
Extended structure of TcO6 octahedron

• TcO2 is insoluble in H2O (solubility 10-8 M)

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2. Tc2O7
Oxidation of TcO2 by O2 at 450 C in a sealed
tube 2 TcO2 (3/2)O2 ? Tc2O7
450 C
O2
Molecular dimer Similar to Mn2O7
Tc2O7
TcO2
Properties
120 C
311 C
solid
liquid
gas

• Tc2O7 is highly volatile and soluble in H2O

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C. Binary halides
Transition metal binary halides MXn (X halide
n 1-7) Prior to 2008, only three technetium
binary halides were known
TcCl4 in 1957
TcF6 in 1961 TcF5 in
1963
Tc xs Cl2 ? TcCl4
Tc xs F2 ? TcF6 Tc xs N2/F2
? TcF5
No binary iodides and bromides reported No
trivalent or divalent Tc binary halides reported
prior 2008
In 2014 Ten binary halides are reported (worked
performed at UNLV)
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Reaction between halides and Tc metal at elevated
temperature in sealed tubes
Tc Br2
Tc Cl2
Tc I2
D

X2
Furnace 250-500 C 6 h-16 days
Tube is flame-sealed
Tc metal in glass tube
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Seven new phases reported
b-TcCl3
AlCl3
280 C
1 mtorr
450 C
TcCl 12.5
450 C
a-TcCl2
b-TcCl2
Tc X2
New structure-type
TcI 14
TcBr 14
400 C
a-TcCl3
TcBr 13
400 C
400 C
TcI3
TcBr3
TcBr4
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D. Other binary compounds
1. Binary Carbides
Reaction between Tc metal and graphite at 1050
C Product depend on TcC ratio For Clt 1
Solid solution of carbon in Tc metal For 1 ltClt
9 Formation of a new phase TcC. Structure
unknown
2. Binary Nitrides
Tc nitride formed by thermal decomposition of
NH42TcCl6 under N2. ? Stoichiometry TcN0.75.
Structure unknown
T 300 ºC
N2
NH42TcCl6
TcN0.75
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3. Binary sulfides
Two sulfides reported Tc2S7 and TcS2 ? Tc2S7
Reaction between TcO4- and H2S in acidic
solution Structure unknown. ? TcS2 formed
by decomposition of Tc2S7 at 1000 C Structure
characterized, isostructural to ReS2
4. Phosphides

• Four binary phosphides Tc3P, Tc2P3, TcP3 and
  TcP4
• Reaction between Tc metal and phosphorous in a
  sealed tube (1000 C)

Structure of TcP3 Edge-sharing TcP6 octahedron
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3. Complexes with multiple metal-metal bonds A.
Generality B. Preparation and structure
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1. Generality
Metal-metal bonded dimers M2n units coordinated
to ligands In the M2n d orbitals can overlap
and form s, p and d bonds Technetium Tc26,
Tc25 and Tc24 unit
For Tc26
For Tc25
For Tc24
Tc2Cl82-
Tc2Cl83-
Tc2Cl4(PMe3)4
quadruple bond
electron-rich triple bond
Bond order of 3.5
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2. Preparation and structure
a) Tc26 (TBA)2Tc2X8
12 M HCl
T 100 C, H2O2 (TBA)OH
cold

• (TBA)TcO4

TcO2/NH4TcO4
(TBA)TcOCl4
(n-Bu4N)BH4 THF

HBr gas
HCl, acetone
T 30 C
(TBA)2Tc2Br8
(TBA)2Tc2Cl8
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Crystallization from acetone / ether for single
crystal XRD ? Formation of an acetone solvate
(TBA)2Tc2X8. 4(CH3)2CO
Tc2X82- ion
Eclipsed TcCl4 units
Anions Tc-Tc (Å) ltTc-Xgt (Å) ltTc-Tc-Xgt ()
Tc2Br82- 2.1625(9) 2.4734(7) 105.01(3)
Tc2Cl82- 2.1560(3) 2.3223(7) 103.92(2)

• Steric effect induced by bromide in Tc2Br82- ion
• Increase of Tc-Tc separation and Tc-Tc-X angle

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b) Tc25 Cs3Tc2X8
1. Disproportionation of Tc2X82- anion in
concentrated HX at 80 C 3 Tc2X82- 4 X- ? 2
TcX62- 2 Tc2X83- 2. Selective precipitation of
TcX62- and Tc2X83- with CsX
CsBr (CsTc 31)
Transfer in centrifuge tube
Precipitation TcBr62-
(TBA)2Tc2Br8 in HBr at 80 C
xs CsBr
Precipitation Tc2Br83-
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Crystallization in concentrated HBr for single
crystal XRD ? Formation of hydrate
Cs(2x)H3O(1-x)Tc2Br84.6H2O (x 0.221)
Tc2X83- ion
Tc2Br83- ion
4.86
Anion Tc-Tc (Å) ltTc-Xgt (Å) ltTc-Tc-Xgt ()
Tc2Br83- 2.1265(9) 2.4732 106.07(3)
Tc2Cl83- 2.1174 2.36315 104.827

• Steric effect induced by bromide in Tc2Br83-
  anion
• Internal rotation angle in Tc2Br83- (4.86)
• d(Tc-Tc) in Tc2Br83- is 0.04 Å shorter than in
  Tc2Br82-

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c) Tc24 Tc2X4(PMe3)4
Disproportionation of (TBA)2Tc2X8 in CH2Cl2/
PMe3 2(TBA)2Tc2X8 6PMe3 ? Tc2X4(PMe3)4
2TcX4(PMe3)2 4(TBA)X
3. Extraction and Recrystallization in hexane
1. Five min under Ar 2. Pumping to dryness
(TBA)2Tc2Br8 in CH2Cl2/ PMe3
Tc2Br4(PMe3)4
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X
P
Tc
TcX2(PMe3)2 units rotated by 105 ? Isomorphous to
M2X4(PMe3)4 (M Re, Mo)
compound Average distances (Å) Average distances (Å) Average distances (Å)
compound Tc-Tc Tc-X Tc-P
Tc2Br4(PMe3)4 2.1316(5) 2.5201 2.4411
Tc2Cl4(PMe3)4 2.1318(3) 2.38585 2.43564

• Tc24 core not sensitive to the nature of
  coordinating halide

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4. Aqueous solution chemistry

• A. Non-complexing media
• Complexing media
• 1. chloride, 2. carbonate

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A. Non-complexing media
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Aqueous species
Speciation depends on redox and acidity of the
solution
Tc(7)
Tc(4)
metal
? 3 species are thermodynamically stable Tc(7),
Tc(4) and Tc metal
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? Disproportionation

• Tc(6), Tc(5), Tc(3) are thermodynamically
  unstable

Tc Reaction
Tc(6) 2Tc(6) ?Tc(7) Tc(5)
Tc(5) 3Tc(5) ? Tc(7) 2Tc(4)
Tc(3) 5Tc(3) ? 4Tc(4) Tc(0)
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B) Complexing media
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1. Chloride media
4 Chloro- species identified in concentrated HCl
Ox. Media Species
6 HCl/H2SO4 TcOCl5-
5 Cold HCl TcOCl52-
4 Warm HCl TcCl62-
2, 3 Warm HCl Zn powder Tc2Cl83-
TcOCl5- anion

• TcO4- is unstable in 12 M HCl reduction of Tc by
  Cl-

Warm HCl
Cold HCl
Cold HCl
TcO4- ? TcOCl5- ? TcOCl52- ? TcCl62-
Further reduction of Tc(IV) in warm HCl by Zn
TcCl62- Zn ? Tc2Cl83- Zn2
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2. Carbonate media

• Presence of carbonate in geological formation
• Tc(IV) and Tc(III) complexes reported in
  carbonate solution
• Structure unknown

O.N Media Structure
IV Neutral HCO3- 0.5 M Reducing media Tc(CO3)q(OH)n(4-n-2q) ?
III Neutral HCO3- 0.5 M Reducing media Tc(CO3)q(OH)n(3-n-2q) ?

• No solid of Tc carbonate synthesized

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5. Summary
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Technetium
Group VII second row transition metal Predicted
145 years ago and discovered 77 years
ago Lightest radioactive element (no stable
isotopes) Two isotopes of interest 99Tc (b-)
fission product of nuclear industry (6 yield
from 235U, 2 tons/y produced) 99mTc(g) produced
from 99Mo decay, imaging agent cardiolite 40
millions treated Presence in environment from
nuclear fuel reprocessing and atomic weapon
test Basic inorganic chemistry Rich redox-
chemistry with 9 oxidations states, chemistry
similar to Re Solid state compounds rich and
unique halides chemistry (i.e., TcCl2
structure-type) Lack of data for nitrides,
sulfides and carbides materials High tendency to
form multiple metal-metal bonds in low valent
states (i.e., Tc2X8n-) Aqueous chemistry Non
complexing 3 oxidation states are
thermodynamically stable (7, 4 and 0) Con. HCl
Tc(6), Tc(5), Tc(4) and Tc(2.5) complexes
characterized Carbonate Tc(4) and Tc(3)
reported but not characterized
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Questions