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Structure studies of sulphur compounds by esca
CHEMICAL
PHYSICS
LETTERS
STRUCTURE
1 (1968)
STUDIES
557-559.
NORTH-HOLLAND
OF SULPHUR
K. HAMRIN,G. JOHANSSON, A. FAHLMAN, Insfifufe
of Physics,
Univevsify
PUBLISHING
COMPANY.
COMPOUNDS C. NORDLING,
of Uppsala,
BY
AMSTERDAM
ESCA
K. SiEGBAHN
Sweden
and
B. LINBBERG Phamacia Received
AB.
Vppsala,
30 November
Sweden 1967
Results, obtained by means of the ESCA-technique (Electron Spectroscopy for Chemical Analysis), are reported on the correlation between the binding energy of the inner electrons of sulphur and the chemical state and environment, with particular emphasis on the sulphur-oxygen bond. A charge-binding energy correlation is established which can be used for the estimation of charge on sulphur in compounds with uncertain structure or composition.
In a previous paper we have shown that the valence state of an element, represented by the oxidation number, can be correlated with line shifts in electron spectra [l]. A qualitative explanation for the observed increase in core electron binding energy with increasing oxidation number was given in terms of a simple free-ion model. The measurements were made on sulphur in compounds with sodium and potassium as cations. Measurements were later ma& by the same method (ESCA, standing for Electron Spectroscopy
were
solids
at room
temperature
Fig. 1. Correlation between 2p electron binding energy of sulphur and calculated charge_ Filled points indicate compounds studied in the solid phase at room temperature. Each point represents the mean value for compounds with the same calculated charge on sulpkr. Open points represent liquids and gases studied with the freezing technique. Squares indicate the two possible structures of o&ho-nitrobenzene-sulphenic ester.
pounds 131. . _ The experimental points define a iinear relationship between core electron energy and calculated charge. For some of the compounds
(filled
January 1968
the structures
z-re uncertainanddiifer-
ent charges can therefore be calculated depending on the choice of structure. If, for exampie, the charge assigned to the sulphur in the ortho-
Liquids and gases (open points) were investigated by means of a cryostat for cooling the source holder below the freezing point of the com-
points).
557
558 .
K. HAMFUN et al.
nitao-benzene-sulphenic ester is based on structure I this point deviates considerably from the correlation However, the measured binding energy, which corresponds to a charge of +0.38, agrees with structure II for which there is evidence in the literature based on X-ray diffraction measurements [6].
q + 0.22
tion on the properties of sulphur containing groups as substituents in aromatic systems, and for variolls reasons a series of nitrophenyl substituted sulphur compounds has been chosen for special study. A large interval of the charge scale in fig. 1 can be encompassed by such series of aromatic sulphur compounds, and fig. 2 shows the spectra of five of these compounds. The sulphur 2p bindiri energy increases as the atomic charge on sulphur increases from compound (a) to compound (e). Two sulphur lines are present in spectrum (e) in accordance with the non-equivalent structural positions of the two sulphur atoms in this compound. Similarly a doublet line structure for oxygen is present in spectrum (b). Effects on the core electron energies of substitution in the benzene nucleus of aromatic sulphur compounds have also been studied This is
q •t 0.44
As mentioned above we have placed special emphasis on the study of sulphur-oxygen bonds. Iiowever, among the compounds investigated there is a lsrge number in which sulphur is also bound to hydrogen, carbon, nitrogen, or halogen. The calculated charge thus correlates very well with the measured core electron energy, independently of the elements forming the bonds to the atoms studied More positive charges can be obtained by attaching fluorine to the sulphur, and we are now extending the correlation by measurements on compounds with sulphur-fluorine bonds. As the first compound in this series we have chosen SOF2 in which the calculated charge on sulphur ((I = 1.30) is still about the same as the highest charge in the sulphur-oxygen series, see fig. 1. We then found that if the flow of SOF2 gas into the source housing was increased the oxygen signal disappeared and a new and broad sulphur line was observed at a considerably higher binding energy. Graphical resolution of this line in two, each with the width normally observed, yielded sulphur 2p binding energies Eb = 173.0 eV and Eb = 175.0 eV. If the correlation obtained from the sulphur-oxygen series is extrapolated towards higher binding energies the corresponding charge values are q = 2.1 and q = 2.5, respectively (see fig. 1). This indicates that the SOF2 contained also some S2FlO and SF6 (calculated charge q = 2.15 and q = 2.58). Sulphurhexafluoride, SF6, has been studied recently in Berkeley [‘7] and the measured 2p binding energy agrees with the extrapolated value from fig. 1. The present study from part of an invest&a- .
I
OX:zEN
NITREGEN
CAR,$ON
SUP$JR
. O,Ne)SO,o
h .3
950
cV*
$55
’
1075 1060
’
405&Q’
’ 1200 ’ KlNEllC ENERGY 285280 ’ BINDING EtEFW
C
1315132OU25
165 160
Fig. 2. Electron spectra of five members of a series of nitro>henyl substituted sulphur compollnds.
c
?
STRUCTURE
STUDIES
OF SULPHUR
COMPOUNDS
BY ESCA
559
phide sulphur is shifted -0.7 eV reIative to the sulphonate sulphur and the spectrum thus reflects the electron donating character of an arematic o-amino group. We thank Fil. kand. U. Gelius znd FL kand. B. Schrbder for helpful assistance. The work has been supported in part by the LJ.S.Air Force through the European Office of Aerospace research, contract AF 61(052)-795.
References [l]
lv
I 170
KINETIC I 165 BINOING
ENERGY 160 ENERGY
Fig. 3. Effects of aromatic substitution on the 2p binding energy of sulphide sulphur in 3-phenylthiopropane sulphonate.
illustrated in fig. 3 which shows the substituent effect of the ol-tlto-amino group on the sulphide sulphur present in 3-phenyl-thiopropane sulphonate.
The
2p electron
binding energy
of the sul-
A. Fahlman, K. Hamrin, J. Hedman. R.Nordberg. C. Nordling and K. Siegbahn. Nature 210 (1966) 4. [2] G.AxeIson, U . Ericson, A. Fahlman. K. Harnrin. J. Hedman. R. Nordberg. C. Nordling and K. Sieghahn. Nature 213 (1967) 70. [3] R.Nordberg, R.G.Albridge, T.Bergmark. U.Ericson, A. Fahlman, K. Hamrin, J. Hedman. G. Johansson. C. Nordline;. K. Siegbahn and B. Lindberg._ Nature 214 (1967) %I. [4j L. Pauling, The nature of the chemical bond. 3rd ed. (New York. 1960). 151 K. Siegbahn. C.NordIing, A. Fahlman. R.Nordherg. K.Hamrin. J. Hedman. G. Johansson, T. Ber,park. S. -E. Karlsson. I. Lindgren and B. Lindberg. Nova Acta Regiae Societatis ScientiaUpsaiiensis. Ser.IV. 19. no.4. [S] W.C.Hamilton. J.Am.Chem.Soc.86 (lSS4) 2289. [7] S_Hagstr6m, Private communication.
PHYSICS
LETTERS
STRUCTURE
1 (1968)
STUDIES
557-559.
NORTH-HOLLAND
OF SULPHUR
K. HAMRIN,G. JOHANSSON, A. FAHLMAN, Insfifufe
of Physics,
Univevsify
PUBLISHING
COMPANY.
COMPOUNDS C. NORDLING,
of Uppsala,
BY
AMSTERDAM
ESCA
K. SiEGBAHN
Sweden
and
B. LINBBERG Phamacia Received
AB.
Vppsala,
30 November
Sweden 1967
Results, obtained by means of the ESCA-technique (Electron Spectroscopy for Chemical Analysis), are reported on the correlation between the binding energy of the inner electrons of sulphur and the chemical state and environment, with particular emphasis on the sulphur-oxygen bond. A charge-binding energy correlation is established which can be used for the estimation of charge on sulphur in compounds with uncertain structure or composition.
In a previous paper we have shown that the valence state of an element, represented by the oxidation number, can be correlated with line shifts in electron spectra [l]. A qualitative explanation for the observed increase in core electron binding energy with increasing oxidation number was given in terms of a simple free-ion model. The measurements were made on sulphur in compounds with sodium and potassium as cations. Measurements were later ma& by the same method (ESCA, standing for Electron Spectroscopy
were
solids
at room
temperature
Fig. 1. Correlation between 2p electron binding energy of sulphur and calculated charge_ Filled points indicate compounds studied in the solid phase at room temperature. Each point represents the mean value for compounds with the same calculated charge on sulpkr. Open points represent liquids and gases studied with the freezing technique. Squares indicate the two possible structures of o&ho-nitrobenzene-sulphenic ester.
pounds 131. . _ The experimental points define a iinear relationship between core electron energy and calculated charge. For some of the compounds
(filled
January 1968
the structures
z-re uncertainanddiifer-
ent charges can therefore be calculated depending on the choice of structure. If, for exampie, the charge assigned to the sulphur in the ortho-
Liquids and gases (open points) were investigated by means of a cryostat for cooling the source holder below the freezing point of the com-
points).
557
558 .
K. HAMFUN et al.
nitao-benzene-sulphenic ester is based on structure I this point deviates considerably from the correlation However, the measured binding energy, which corresponds to a charge of +0.38, agrees with structure II for which there is evidence in the literature based on X-ray diffraction measurements [6].
q + 0.22
tion on the properties of sulphur containing groups as substituents in aromatic systems, and for variolls reasons a series of nitrophenyl substituted sulphur compounds has been chosen for special study. A large interval of the charge scale in fig. 1 can be encompassed by such series of aromatic sulphur compounds, and fig. 2 shows the spectra of five of these compounds. The sulphur 2p bindiri energy increases as the atomic charge on sulphur increases from compound (a) to compound (e). Two sulphur lines are present in spectrum (e) in accordance with the non-equivalent structural positions of the two sulphur atoms in this compound. Similarly a doublet line structure for oxygen is present in spectrum (b). Effects on the core electron energies of substitution in the benzene nucleus of aromatic sulphur compounds have also been studied This is
q •t 0.44
As mentioned above we have placed special emphasis on the study of sulphur-oxygen bonds. Iiowever, among the compounds investigated there is a lsrge number in which sulphur is also bound to hydrogen, carbon, nitrogen, or halogen. The calculated charge thus correlates very well with the measured core electron energy, independently of the elements forming the bonds to the atoms studied More positive charges can be obtained by attaching fluorine to the sulphur, and we are now extending the correlation by measurements on compounds with sulphur-fluorine bonds. As the first compound in this series we have chosen SOF2 in which the calculated charge on sulphur ((I = 1.30) is still about the same as the highest charge in the sulphur-oxygen series, see fig. 1. We then found that if the flow of SOF2 gas into the source housing was increased the oxygen signal disappeared and a new and broad sulphur line was observed at a considerably higher binding energy. Graphical resolution of this line in two, each with the width normally observed, yielded sulphur 2p binding energies Eb = 173.0 eV and Eb = 175.0 eV. If the correlation obtained from the sulphur-oxygen series is extrapolated towards higher binding energies the corresponding charge values are q = 2.1 and q = 2.5, respectively (see fig. 1). This indicates that the SOF2 contained also some S2FlO and SF6 (calculated charge q = 2.15 and q = 2.58). Sulphurhexafluoride, SF6, has been studied recently in Berkeley [‘7] and the measured 2p binding energy agrees with the extrapolated value from fig. 1. The present study from part of an invest&a- .
I
OX:zEN
NITREGEN
CAR,$ON
SUP$JR
. O,Ne)SO,o
h .3
950
cV*
$55
’
1075 1060
’
405&Q’
’ 1200 ’ KlNEllC ENERGY 285280 ’ BINDING EtEFW
C
1315132OU25
165 160
Fig. 2. Electron spectra of five members of a series of nitro>henyl substituted sulphur compollnds.
c
?
STRUCTURE
STUDIES
OF SULPHUR
COMPOUNDS
BY ESCA
559
phide sulphur is shifted -0.7 eV reIative to the sulphonate sulphur and the spectrum thus reflects the electron donating character of an arematic o-amino group. We thank Fil. kand. U. Gelius znd FL kand. B. Schrbder for helpful assistance. The work has been supported in part by the LJ.S.Air Force through the European Office of Aerospace research, contract AF 61(052)-795.
References [l]
lv
I 170
KINETIC I 165 BINOING
ENERGY 160 ENERGY
Fig. 3. Effects of aromatic substitution on the 2p binding energy of sulphide sulphur in 3-phenylthiopropane sulphonate.
illustrated in fig. 3 which shows the substituent effect of the ol-tlto-amino group on the sulphide sulphur present in 3-phenyl-thiopropane sulphonate.
The
2p electron
binding energy
of the sul-
A. Fahlman, K. Hamrin, J. Hedman. R.Nordberg. C. Nordling and K. Siegbahn. Nature 210 (1966) 4. [2] G.AxeIson, U . Ericson, A. Fahlman. K. Harnrin. J. Hedman. R. Nordberg. C. Nordling and K. Sieghahn. Nature 213 (1967) 70. [3] R.Nordberg, R.G.Albridge, T.Bergmark. U.Ericson, A. Fahlman, K. Hamrin, J. Hedman. G. Johansson. C. Nordline;. K. Siegbahn and B. Lindberg._ Nature 214 (1967) %I. [4j L. Pauling, The nature of the chemical bond. 3rd ed. (New York. 1960). 151 K. Siegbahn. C.NordIing, A. Fahlman. R.Nordherg. K.Hamrin. J. Hedman. G. Johansson, T. Ber,park. S. -E. Karlsson. I. Lindgren and B. Lindberg. Nova Acta Regiae Societatis ScientiaUpsaiiensis. Ser.IV. 19. no.4. [S] W.C.Hamilton. J.Am.Chem.Soc.86 (lSS4) 2289. [7] S_Hagstr6m, Private communication.