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Neil Bartlett’s Discovery of Noble-Gas Reactivity;
Its Aftermath and Significance
University of Oulu, Finland
Main-Group Chemistry Summer School
August 27-31, 2012
Lecture I
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Beginning of the noble-gas story at King’s College,
Newcastle, England
• Neil Bartlett, a Ph.D. student, wanted to study the preparation of PtF2 by reduction of PtF4. PtF4 was contaminated by bromine.
• Bartlett heated impure PtF4 in F2 to oxidize the bromine to BrF5, with the hope that this would liberate BrF5 from the PtF4. The fluorination was done in a stream of diluted fluorine in a shallow Ni boat, placed in a Pyrex glass tube. When heated, the PtF4 became darker. Finally, a deep red vapor emerged from the boat and condensed on the cooler glass downstream. This occurred just as it became clear that the fluorine was attacking the glass tube to liberate oxygen and SiF4.
• PtF4, already known in November 1956, was the highest known Pt fluoride.
• Bartlett initially concluded that he probably obtained a new oxide fluoride of platinum, PtO2F6.
3Pt + 4BrF3 3PtF4 + 2Br2
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Continuation of the story at the University of British
Columbia, Canada
• Bartlett continued his research on PtO2F6 at UBC. He found that the solid was paramagnetic, ruling out the possibility of PtX.
• The X-ray powder diffraction pattern contained a strong set of lines indicative of a simple cubic Pt-atom sublattice.
• Slow hydrolysis of the compound gave PtF62− as a solution species
indicating that the compound was a "PtF6" species.
• Together with its magnetic properties, the formulation, O2+PtF6
−, was suggested.
• From simple lattice energy considerations, it was concluded that electron affinity of PtF6 should exceed 7 eV.
• This led Bartlett to attempt to oxidize xenon.
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Bartlett’s comments regarding the synthesis of
O2+PtF6
−
• The discovery of O2
+PtF6− was accidental.
• O2+PtF6
− was easily made but its correct characterization probably
involved, according to Bartlett, the most difficult work of his entire
career.
• Both ions were then unknown in chemical compounds.
• Oxidation of oxygen required that PtF6 be a one electron oxidizer of
unprecedented strength.
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O2+
(g) + PtF6−
(g)
O2(g) + PtF6(g) O2+PtF6
−(s)
< 648 (EA)
1171
(IP) 523 (lattice energy)
Born-Fajans-Haber Cycle for O2+PtF6
−
(enthalpies in kJ mol–1)
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He Ne Ar Xe
He+ 24.6
Ne+
21.6 Ar+ 15.8 Kr+
14.0 Xe+ 12.1 eV
Atomic Diameters 260 320 384 396 436
Kr
Ionization Energies (eV) and Diameters of
Noble- Gas Atoms (pm)
Ionization potential for Ng(g) Ng+
(g) + e
1eV = 96.49 kJ mol–1, 23.06 kcal mol–1
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Thermal Chemistry of the Reactions of O2 and
Xe with PtF6 (kJ mol–1)
O2 (g) O2+
(g) + e− H = 1171
Xe (g) Xe+(g) + e− H = 1167
PtF6 (g) + e− PtF6−
(g) H = 750
Xe(g) + PtF6 (g) Xe+(g) + PtF6
–(g) H = 417
Xe+(g) + PtF6
– (g) "Xe+PtF6
–(s)" –HL = –460
Xe(g) + PtF6 (g) "Xe+PtF6–
(s)" H ≈ –43
NOTE: Although G may be +ve at room temperature (TS is –ve),
the actual structure of XePtF6 is unknown.
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From the introduction to the book “The Oxidation
of Oxygen and Related Chemistry” by Neil Bartlett:
“Genuine new directions in research are
unanticipated. They are unlikely to be part of a
research proposal. It is the unanticipated event (such
as the first observation of O2PtF6) which is so
important, and has to be followed up. A new
viewpoint then develops. In such a way Noble-Gas
Chemistry was born.”
World Scientific Series in 20th Century Chemistry – Vol. 9, 2001
12
2006 International Historic Chemical Landmark Dedication
University of British Columbia, Vancouver
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“Neil Bartlett and Reactive Noble Gases”
“In this building in 1962 Neil Bartlett demonstrated
the first reaction of a noble gas. The noble gas
family of elements - helium, neon, argon, krypton,
xenon, and radon - had previously been regarded
as inert. By combining xenon with a platinum
fluoride, Bartlett created the first noble gas
compound. This reaction began the field of noble
gas chemistry, which became fundamental to the
scientific understanding of the chemical bond. Noble
gas compounds have helped create anti-tumor
agents and have been used in lasers.“
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Synthesis of the First Noble-Gas Compound
XePtF6 + PtF6 XeF+PtF6− + PtF5
xPtF6 + Xe Xe(PtF6)x 1< x < 2 sticky red-colored solid
XRDP of the product Xe(PtF6)X always exhibited the characteristic pattern
of XeF+PtF6− (identical to that of XeF+RuF6
−).
Conclusion:
Xe(PtF6)2 XeF+Pt2F11− orange red friable solid
XeF+PtF6− + PtF5 XeF+Pt2F11
−
XRDP shows only XeF+PtF6−
analogous and isomorphous
with XeF+Ir2F11−
L. Graham, O. Graudejus, N. K. Jha, N. Bartlett Coord. Chem. Rev.
2000, 197, 321-334.
T < 60 °C
T < 60 °C
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The Best Preparation of “XePtF6”
PtF6 (diluted 1:6 in SF6) + Xe (in excess) “XePtF6”
XePtF6, a mustard-yellow solid, gave neither a Raman spectrum nor XRDP. It
neither reacted nor dissolved in aHF, the color suggested that PtF5 was absent.
It is weakly paramagnetic (small quantities of XeF+PtF6− and PtF5 are present
even in the best preparations). XePtF6, when pure, may be a relative of
diamagnetic XePdF6.
L. Graham, O. Graudejus, N. K. Jha, N. Bartlett Coord. Chem. Rev. 2000, 197, 321-334.
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Reaction of PtF4 and XeF2 in aHF solvent
2XeF2 (solv) + PtF4 (s) 2XeF+(solv) + PtF6
2− (solv)
aHF
multi-fold excess of XeF2 yellow solution
n(XeF+)2PtF62− nXeF2 + (XeF+)n(PtF5
−)n
removal of aHF
“XePtF6”
diamagnetic yellow solid
PtF62− in aHF is probably stabilized by solvation and
therefore less strongly polarizes the XeF+(solv) cation,
which, after removal of aHF, gives the strongly
polarizing “naked” XeF+ cation. This is capable of
removing F− from PtF62− to yield PtF5
−, which could
then oligomerize.
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Can we speculate about the structure of XePtF6?
Diamagnetic XeIIPtIVF6 (probably the polymeric salt (XeF+)n(PtF5−)n is the
thermodynamically preferred form of “XePtF6”. The products of the further
oxidation by PtF6 are Pt(V) derivatives XeF+PtF6−, XeF+Pt2F11
−, and PtF5.
The structure of XePtF6 is not yet known. Based on Bartlett’s
considerations, the structure should be akin to the structure of the
polymeric salt (XeF+)n(CrF5−)n.
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(XeF+)n(CrF5−)n
mCrF5 + nXeF2 mXeF2·CrF4 + 0.5mXeF4 + (n – 1.5m)XeF2
n > 5m
K. Lutar, I. Leban, T. Ogrin, B. Žemva, Eur. J. Solid State Inorg. Chem., 1992.
50°C
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Rapid Development of Noble-Gas Chemistry
Experimental Techniques Then Available
Metal vacuum lines and inert fluoroplastics (Kel-F, Teflon).
For handling F2 and aggressive fluorine compounds.
Synthetic fluorine chemistry expertise at that time
and metal hexafluoride chemistry (Manhattan project).
Physical Methods for Structural Characterization:
Diffraction methods (neutron & X-ray)
Vibrational spectroscopy (Raman & Infrared)
Nuclear magnetic resonance
Mössbauer spectroscopy
Mass spectrometry
Electron spin resonance
Thermochemistry
Theoretical studies
404 pages
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Geometries of Noble-Gas Compounds Predicted by VSEPR
R. J. Gillespie In Noble Gas Compounds; H. H. Hyman, Ed.; University of Chicago Press:
Chicago, 1963, pp 333−339.
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XeF2 1962
XeF4 1962
XeF6 1962
XeO3 1962
KrF2 1963
XeOF4 1963
XeO64– 1963
XeO4 1964
XeO2F2 1967
XeO3F2 1968
Most noble-gas chemistry precursors
were prepared within 2 years of Neil
Bartlett’s discovery
Stable compounds of Xe and Kr were formed having the oxidation
states: Xe(II), Xe(IV), Xe(VI), Xe(VIII) and Kr(II).
Only Xe–F, Xe–O, Kr–F bonds were known.a
The Early Years
H. H. Hyman’s edited book “Noble-gas Compounds”
a Transient Xe-Cl bonds were formed by radioactive decay of 129ICl2 and 129ICl4
to 129mXeCl2 and 129mXeCl4. XeCl2 and XeCl4 were detected by their 129Xe Mössbauer
emission spectra.
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Xe–N 1974
Xe–Xe 1978
Xe–Cr 1983
Kr–N 1988
Kr–O 1989
Xe–C 1989
Xe–W 1992
Xe–Mo 1996
Ng–M 1996 Ng = Ar, Kr, Xe; M = Cr, Mo, W
Xe–Au 2000
Xe–Re 2000
Ar–H b 2000
Ar–F b 2000
Xe–Cl 1999, 2001
Xe–Hg 2003
a Stable in solution and/or the solid state. b Matrix-isolation study.
The Quest for Stablea Bonds with Noble-Gases
28
Xe–N Bond
FXeN(SO2F)2
• X-ray crystal structure of the first Xe-N bonded compound
J. F. Sawyer, G. J. Schrobilgen, S. J. Sutherland, Inorg. Chem. 1982, 21, 4064-4072.
R. D. LeBlond, D. D. DesMarteau, J. Chem. Soc., Chem. Commun. 1974, 555.
XeF2 + HN(SO2F)2 FXeN(SO2F)2 + HF CF2Cl2
0 oC, 4 days
–55 oC
Some Synthetic & Structural Highlights
Since Neil Bartlett’s Discovery
29
D. Naumann, W. Tyrra, J. Chem. Soc., Chem. Commun. 1989, 47–50.
H.-J. Frohn, S. Jakobs, J. Chem. Soc., Chem. Commun. 1989, 625–627.
H.-J. Frohn, S. Jakobs, G. Henkel, Angew. Chem., Int. Ed. Engl. 1989, 28, 1506–1507.
B(C6F5)3 + XeF2 [C6F5Xe][B(C6F5)nF4–n] CH2Cl2 or CH3CN
–50 oC or –40 oC
K. Koppe, H.-J. Frohn, H. P. A. Mercier, G. J. Schrobilgen, G. J., Inorg. Chem. 2008, 47, 3205–3217.
[C6F5Xe][BF4] + M[BY4] [C6F5Xe][BY4] + M[BF4]↓ CH3CN
RT to –40 °C
Y = CF3, CN, C6F5
M = K, Cs
Xe–C 2.081(3) Å
Xe –C Bonds II
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Bock, H.; Hinz-Hubner, D.; Ruschewitz, V.; Naumann, D. Angew. Chem., Int. Ed. 2002, 41, 448–450.
2(CH3)3SiC6F5 + XeF2 Xe(C6F5)2 + 2(CH3)3SiF [N(CH3)4][F]
CH2Cl2, –78 oC
Xe –C Bonds II
Xe–C av. 2.37(1) Å
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C6F5BF2 + XeF4 [C6F5XeF2][BF4] ↓
Xe –C Bond
Xe–C 2.064(8) Å
K. Koppe, H.-J. Frohn, H. P. A. Mercier, G. J. Schrobilgen, G. J., Inorg. Chem., to be published.
IV
CH2Cl2
–55 °C
H.-J. Frohn, N. LeBlond, K. Lutar, B. Žemva, Angew. Chem., 2000, 112, 405.
32
S. Siedel, K. Seppelt, Angew. Chem., Int. Ed. 2001, 40, 4225–4227.
Xe–Cl Bond
XeF+ + Cl– XeCl+ + F–
yellow orange
Xe–Cl 2.306(2) Å
HF/SbF5
–30 oC to RT
(C6F5Xe)2Cl+
XeCl 2.784(2), 2.847(1) Å
H.-J. Frohn, T. Schoer, G. Henkel, Angew. Chem., Int. Ed. 1999, 38, 2554–2556.
33
L. Stein, W. W. Henderson, J. Am. Chem. Soc. 1980, 102, 2856.
T. Drews, K. Seppelt, Angew. Chem. Int. Ed. Engl. 1997, 36, 273.
Xe–Xe Bond
Xe2+(Sb4F11
–)2
intense green
XeF+SbnF5n+1– + 3Xe + nSbF5 2Xe2
+SbnF5n+1–
Xe–Xe 3.087 Å
HF/SbF5
34
S. Seidel, K. Seppelt, Science 2000, 290, 117–118.
T. Drews, S. Seidel, K. Seppelt, Angew. Chem. Int. Ed. 2002, 41, 454–456.
Xe–Au Bond
AuF3 + 6Xe + 3H+ AuXe42+ + Xe2
+ + 3HF
Xe–Au 2.739(1) Å
HF/SbF5
–40 oC
AuXe42+(Sb2F11
–)2
dark red
35
I. C. Hwang, S. Seidel, K. Seppelt, Angew. Chem. Int. Ed. 2003, 42, 4392–4395.
Xe–Hg Bond
HgF2 + xsXe + 3SbF5 HgXe2+ + SbF6– + Sb2F11
–
Hg–Xe 2.76 Å
SbF5
60 oC
HgXe2+(SbF6–)(Sb2F11
–)
colorless
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15N, 99.5% 82Kr, 11.8% 82Kr, 11.3%, I = ½, WF = 5.4 84Kr, 57.0% 86Kr, 17.3%
1J(13C–15N) = 312 Hz 2J(15N–1H) = 12.2 Hz 4J(19F–1H) = 4.2 Hz 2J(19F–15N) = 26 Hz 3J(19F–13C) = 25.0 Hz
G. J. Schrobilgen, J. Chem. Soc., Chem. Commun. 1988, 863-865.
HC≡N + AsF5 + HF HC≡NH+AsF6–
HF
–78 oC
Kr–N Bond
HC≡NH+AsF6– + KrF2 HC≡NKrF+AsF6
– + HF BrF5
–57 oC
G. J. Schrobilgen, J. Chem. Soc., Chem. Commun. 1988, 1506-1508.
• RFC≡NKrF+ (RF = CF3, C2F5, n-C3F7) are also known
37
–40 to RT N(CH3)4
+F– + XeF4 N(CH3)4+XeF5
–
CH3CN
Xe–F av. 2.012(4) Å
F-Xe-F av. 72.0(9)o
K. O. Christe, E. C. Curtis, D. A. Dixon, H. P. Mercier, J. C. P. Sanders, G. J. Schrobilgen,
J. Am. Chem. Soc. 1991, 113, 3351-3361.
First AX5E2 Species
38 38
[Cd(XeF2)8](SbF6)2 [Cd2(XeF2)10](SbF6)4
Coordination Chemistry of XeF2
. XeF2 forms adducts with metal cation centers, e.g., (Mn+(XeF2)p)(AF6
–)n
where
M = Li, Ag(I), Mg, Ca, Sr, Ba, Cu, Zn, Cd, Pb(II), La, Nd(III)
A = P, As, Sb
M. Tramšek, B. Žemva, J. Fluorine Chem. 2006, 127, 1275.
•
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• Prepared by irradiation of HF at 265 oC in an 36/40Ar matrices
deposited on CsI.
• Characterized by IR spectroscopy and quantum-chemical
calculations the compound only exists if maintained below
233 oC, whereupon it evaporates.
L. Khriachtchev, M. Pettersson, N. Runeberg, J. Lundell, M. Räsänen, Nature, 2000, 406, 874–876.
L. Khriachtchev, M. Pettersson, A. Lignell, M. Räsänen, J. Am. Chem. Soc., 2001, 123, 86108611.
The First Argon Compound; Argon Fluorohydride (HArF)
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The Legacy of Neil Bartlett’s Discovery
Although compounds having expanded valence octets were known for nearly two-thirds
of the main-group nonmetals prior to Bartlett’s discovery, the success of valency theory
enforced the notion that filled octets are to be associated with stability.
The synthesis of ‟XePtF6” resulted in a flurry of synthetic and structural work in the field
that quickly revealed the true nature of two of the group 18 elements, xenon and krypton,
and laid waste to the octet myth, then prevalent in chemistry textbooks.
Noble-gas chemistry has provided stimuli to investigate bonding in so-called
“hypervalent” compounds and has contributed to developments in the field of high-
oxidation states of the metals and nonmetals.
The synthesis and structural characterization of noble-gas compounds has burgeoned to
become an intriguing and highly challenging topic in contemporary inorganic chemistry.
Noble-gas chemistry is a vibrant field rife with interesting new compounds, bonding
modalities, rich structural chemistry, and many synthetic applications.
The rapidity of continued developments in noble-gas chemistry are intimately tied to
those who have the skills to confront its challenges and those who have the courage and
foresight to fund curiosity-driven research.
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