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Existence and Bond Energy of the Cesium Auride Molecule.

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Cs2WOS3(0.35 g) in H 2 0 (100 ml). After briefly shaking, the
aqueous phase is separated off and the organic phase is covered with a mixture of n-pentane (50 ml) and acetone (10
ml). After ca. 3-4 d orange-yellow crystals of (1) separate
out (yield 0.05 8).
Received: December 21. 1978 [ Z 268 IE]
revised: April 20. 1979
German version: Angew. Chem. 91, 656 (1979)
[ I ] H Vahrenkamp, Angew. Chem. X7, 363 (1975); Angew. Chem. Int. Ed. Engl.
14. 322 (1975).
121 For the synthesis of biochemically interesting iron-sulfur-molybdenum cage
systemc cf. T. E. Wolf, J . M . Berg. C. Warrick. K. 0.Hudgsun, R. H. Holm,
R. E. Frankel. J. Am. Chem. Soc. IUO. 4630 (1978): G. Chri.sfou, C. D.Gurner,
F E Mabbs. T. J. King. J Chem. SOC.Chem. Commun. IY7X. 740.
131 D M. L. Goodgame, G. A. Leach, A . C. Skapyki. K. A . Woode, Inorg. Chim.
Acta 31. L375 (1978): E. H . Grifrh, C W. Hunr. €. L. Amma. J. Chem. Soc.
Chem. Commun. 1976. 432: D.Cuucuuwnis. D. Swenson, N. C. Baenziger. R.
Pedelry, M . L. Caqer~v.J . Am. Chem. Soc. YY, 8097 (1977): and references
cited therein.
[4] On the problem of metal-metal bonding of Cu' with its closed valency shell
cf. P. K. Mehrorra, R. Huffmann, Inorg. Chem. 17, 2187 (1978).
(51 E. A . Acerill, T. Herskouilz, R. H. Holm. J. A. Ibers, J. Am. Chem. Soc. YS,
3523 (1973).
(61 K. I!. Schmidt, A . Mdller. Coord. Chem. Rev. 14, 115 (1974).
gon and the cell then directly attached to the mass spectrometer.
The mass spectrum obtained at 60 eV and 70 FA showed
in addition to Cs + ,Cs", and A u' a distinct signal for
CsAu+. In the temperature range 1200-1500 K the intensity of the signal at m/e=330 is weaker by a factor of about
lo3 than that of the Cs+ signal. Figure 1 shows plots of the
ionization curves of CsAu + and Au + obtained at a Knudsen
cell temperature of 1490 K.
I'
/
/
i
Existence and Bond Energy of the Cesium Auride
Molecule
8
/
i
i
i
i
Au+
/!'
10
'*
15
12
-
E/eV
By Bernd Busse and Konrad G. WeZl[']
As prototypes of the metal-metal bond, isolated dimeric
and oligomeric metallic species are investigated primarily by
matrix isolation techniques[''. This method, however, has the
disadvantage that the properties of the species investigated
can be strongly influenced in an, as yet, unclear manner by
interaction with the matrix material. Mass spectrometry of
metal vapors permits observation of not only the metal atoms
but also dimers and oligorners. Investigations on binary systems can thus afford valuable information on the existence
and properties of heterometallic molecules. We have therefore started a series of studies on systems in which there is a
large difference in electronegativity of the metal partners-in
anticipation of finding molecules having predictable bonding character in such systems.
As the phase diagram of cesium-gold121shows, this system
forms a n intermetallic compound with a 1 : l composition
which crystallizes with a CsC1-type structure and has a melting point of 590°C. In the liquid state it exists as a purely
ionicmeltr3'.A stable molecule CsAu can be expected to exist
in the vapor phase. In our experiments we used a MM 30 K
mass spectrometer (VG-Micromass) especially developed for
investigations by the Knudsen method (collector system with
conversion dynodes, no mass discrimination). The ionization
was achieved by electron impact. For preparation of the intermetallic compound stoichiometric amounts of the components --pure cesium, packed and stored under high vacuum
(Merck), and pure gold (Degussa), cut into small pieceswere weighed under pure argon into a molybdenum Knudsen cell. The cell, sealed by a screw-top lid, was heated briefly
in an evacuated oven at the melting temperature of gold and
then annealed for 5-6 h at 700°C. After cooling, an effusion orifice in the cell was rapidly opened in a stream of ar['I
Prof' Dr. K. G . Weil. DiplLIng. 6. Busse
Inslitut fur Physikalische Chemie der Technischen Hochschule
Petersenstrasse 20, D-6100 Darmstadt (Germany)
An,qen. Chem. In!. Ed Enal I1 (107Oi No. X
';.
7
,
6
Fig. 1 . Ioni7,ation curves of CsAu ' and Au
*
E / eV
' Ion current
in arbitrary units
Extrapolation of the curves gave appearance potentials of
6.6 k 0.3 eV for CsAu and 9.0 0.3 eV for Au . As a rule of
thumb, an appearance potential near to the mean value of the
ionization potentials of its atoms can be expected for molecules without free valence electrons. For Cs and Au this
leads to 6.55 eV. The experimental value for A u + agrees
within the limits of error with the ionization potential of Au
(9.22 eV).
A decrease in the slope of the ionization curve of CsAu+
at 8.7 eV can be interpreted in terms of the fragmentation
process
+
+
A corresponding increase in the slope of the ionization curve
of Cs' is not observable since the differences in intensity of
the two reaction channels for formation of Cs' are too
great.
Conclusions on the bond energy of the molecule can be
drawn from the fragmentation energy if the ionization potentials of the fragment ions are known and if it can be assumed
that the fragmentation products are formed without additional kinetic energy.
0 Verlag Chemie, GmbH, 6940 Wernheim. IY7Y
0570-0133/79/010x-(l(,7"
p
02 SO/O
629
Thus, from a thermodynamic cycle we obtain for the bond
energy
ported"] to be z7 x lo'. Since alkyl substitution is not expected to change this value significantly, it may safely be assumed that practically all the Ag ions are in the complexed
state. All the experiments were carried out at concentrations
above the CMC of (1)' Ag'. i. e. 3.3 x 10 mol/l. The molecular weight of the relatively large micellar aggregates
(6.3 x 10') was determined by quasielastic light scattering.
In the photochemical reduction of Ag' in ( I ) .Ag ' , the
cyanine dye (2) was used as a sensitizer. This dye absorbs in
+
D(CsAu) = A E * - I ( C s ) = 8.7 e V -4.0 e V =4.7 e V
%460+30 kJ/mol
At first sight this value appears astonishingly high; however,
it is consistent with the expected formation of an ionic bond
due to the difference in electronegativities of gold and cesium. Calculation of the bond energy from the electronegativities and known dissociation energies of the dimers Cs2
and Au2 according to PuulingI4' gives a value of 430 kJ/mol.
Also interesting is a comparison with the isostructural CsC1,
for which the value D(CsC1) =444 kJ/mol was found"].
Our findings clearly indicate that the stability of the cesium auride molecule is essentially determined by ionic
bonding, with cesium acting as the donor and gold as the acceptor.
Received: April 24. 1979 [Z 269 IE]
German version: Angew. Chem. 91. 664 (1979)
CAS Registry numher:
C5Au. 12256-37-0
[ I ] B. Myver. Ber. Bunsenges. Phys. Chem. 82. 24 (1978).
(21 R. P Elliot: Constitution of Binary Alloys. 1st Suppl. McGraw-Hill. New
York 1965.
[3] H . Horhino. R. W. Schmurzler. F H m . d . Phys. Lett. S/ A . 7 (1975)
[4] L. Puuling: Die Natur der chemischen Bindung Verlag Chemie. Weinheim
1973
IS] L. B r e w r . E. Brucker. Chem. Rev. 61. 425 (1961).
the visible region[41(A,,, = 500 nm) and due to Its hydrophobic nature is expected to associate quantitatively with
(I).Ag. In solutions of simple micelles such as sodium laurylsulfate (2) displays a strong fluorescence (c#+= 0.45). This
emission is totally quenched (& < lo-') in micellar solutions
of ( I ) . Ag +. On illumination with visible light, rapid bleaching of the cyanine and formation of a new stable absorption
band with a maximum at A=415 nm is observed (Fig. 1).
The hydrophobic species produced is hence readily extracted
into a chloroform solution (An,.sx = 410 nm; Fig. 1).
Complexes of Nitrogen-Containing Crown Ether
Surfactants with Stable Silver Atoms[**]
By Robin Humphry- Baker, Michael Gratzel, Pietro Tundo,
and Ezio Pelizzetti'']
Nitrogenous crown ethers bearing long alkyl chains as
substituents, such as ( l ) , are surfactants, form micelles, and
complex cations['.']. We have now succeeded in reducing the
complex ( I ) . Ag photochemically and thermally to ( 1 ) .AgU.
The complexed silver atoms d o not aggregate to form clusters or crystalline silver.
X [nml
+
-
Fig. I Absorption spectra of (/).Ag" (a) 8 . 5 ~10
8.5 x I0 'M in HdO.
'M
in CHCI, and (b)
n
n
co
07
Y4-Y
The complex (1).Ag is formed spontaneously on treatment of 2-tetradecyl-l,4,10,13-tetraoxa-7,16-diazacyclooctadecane ( I ) (see ref. [*I for synthesis) with equimolar
amounts of AgNO,. The binding constant of Ag' ion with
the crown ether containing no alkyl side chain has been re+
Prof. Dr P. Tundo
lstituto di Chimica Organica. Universitk di Torino (Italy)
[**I Support of this work by the Swiss National Foundation (Grant No.
4.061.076.04) and Ciba-Geigy. Basel (Switzerland) is gratefully acknowledged
Wcinheim. 1979
The dynamics of the photoreaction of (2) with (1)' Ag
were examined by laser photolysis. A 15 ns pulse of a Qswitched Nd-laser was used to excite the cyanine and resulting changes in the absorbance of the solution were monitored by kinetic spectroscopy (Fig. 2). An irreversible bleach+
Prof. Dr E. Pelizetti
lstituto di Chimica Analitica. Unwersiti di Torino (Italy)
0 Verlug Chemie. CmbH. 694fJ
-1p
Fig. 2. Transient traces recorded on laser excitation (532 nm) of 1.0 x 10 " mol/l
of ( 2 ) in ( / ) . A g ' micelles. ( a ) Absorption ot'(/).Ag" (415 nm) and (b) hleachmg
of the ground-state absorption of 12) (500 nm).
[*] Prof. Dr. M. GrBtzel. Dr. R. Humphry-Baker
Institut de chimie physique. Ecole Polytechnique Federale
CH-IOIS Lausanne (Swit7erland)
630
-
(J570-OX33/79/080X0630 $ 02.50/0
A n g ~ r , C'hrm.
.
/ill.
Ed. Engl I X (iV70) N o 8
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bond, molecules, energy, existencia, auride, cesium
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