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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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Neil Bartlett in his laboratory in 1962

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Oxidation of Xenon with PtF6

N. Bartlett, Proc. Chem. Soc. 1962, 218.

Xe + PtF6 "Xe+PtF6–" 20 oC

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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

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2006 International Historic Chemical Landmark Dedication

University of British Columbia, Vancouver

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International Historic Chemical Landmark (2006)

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

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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

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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.

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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.

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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

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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

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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

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–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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Neil Bartlett Sept. 15, 1932 – Aug. 5, 2008

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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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