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Individual Steps in the Chemisorption of Gases on Metals.

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ides; 2. electrophilic attack, for instance on phosphines and
amines; 3. nucleophilic attack, for instance on Schiffs bases;
and 4. 1,3-dipolar insertions into C-H bonds, for instance
with benzaldehyde. R . W. Murray (Murray Hill, New Jersey)
discussed the route from primary ozonide to ozonides on the
basis of extensive experimental material. The Criegee mechanism needs some extensions. The intermediate stages (IZ)
and (12) were brought into the discussion o n the basis of
stereochemical and crossing experiments, as well as labeling
experiments with deuterium or 1 8 0 .
,P-9
-4 ? (12)
A0+-
.
R . Criegee (Karlsruhe, Germany) showed that aldozonides
from styrene and substituted styrenes are cleaved t o aldehyde
and acid by some solvents, particularly rapidly by methanol.
A diozonide isomerizes under acid catalysis to a compound
that contains two peroxide groups and two acetal oxygen
atoms.
[VB 104 IEI
non-monotonic course of any flow-driving force relation is
the kinetic principle.
Lecture at Kiel (Germany), on October 19, 1967
[VB 105 IE]
German version: Angew. Chem. 80, 156 (1968)
[*] Doz. Dr. W. Seidel
Institut fur Physikalische Chemie der Universitat
23 Kiel, Olshausenstr. (Germany)
[l] Cf. H . L. Heatcoat, Z . physik. Chem. 37, 368 (1901).
[Z] U . F. Franck, Ber. Bunsenges. physik. Chem. 68, 876 (1964).
[3] U. F. Franck, 2. physik. Chem. N.F. 3, 183 (1955).
[4] A. L . Hodgkin, A . F. Huxley, and B. Katz, J. Physiology 116,
424 (1952).
[51 K . F. Bonhoeffer, Naturwissenschaften 40, 301 (1953), and
further literature cited there.
[6] U . F. Franck, 2. Elektrochem. angew. physik. Chem. 55, 535
(1951); Chem.-1ng.-Techn. 38, 612 (1966); and further literature
cited there.
Condensation of D-Glucose with Aromatic Systems
in Liquid Hydrogen Fluoride
German version: Angew. Chem. 80, 125 (1968)
By F. &ficheel[*]
The Kinetic Principle of Excitable Systems
By W. Seidel[*J
About 70 years ago W . 0stwald“J noted in the behavior of
the system Fe/HNO3 remarkable analogies to phenomena
that were known in excitation physiology. This finding
suggested that a chemical kinetic principle exists that is
capable of generalizationand is not confined to living systems.
In fact, many such, so-called “kinetic” model systems are
known, and the analogies of their functioning to that of living
systems that can undergo excitation is so astonishingly
extensive that “no biological phenomenon of excitation is
known that cannot be simulated by a kinetic model” 121.
The most obvious characteristic of all these systems is an
“either-or” behavior that results from the ability of the
system t o exist in two different (stationary) states. Like the
living systems, the models are open systems in the thermodynamic sense; a stationary state arises only if an inward
flow from the environment compensates the outward flow
from the system. These flows are caused by driving forces that
originate from an energy or a potential difference. A superposition of the relations between flow and driving force for
the system and for its surroundings should make it possible
t o interpret the behavior observed.
It can be clearly shown[3J how, for instance, superposition
of a “load line” on a non-monotonic N-shaped characteristic
of a system leads to the existence of two stable stationary
states which are separated by a n unstable one. If the characteristic of the system can shift relative to the characteristic
of the evironment, because of the chemical kinetics, then an
“either-or” behavior can be explained.
In the nerve-cell membrane the phenomenon of excitability is
of electrochemical nature [41. Like most model systems, the
Fe/HNO3 system, later called the Ostwald-Lillie nerve model,
also belongs t o electrochemistry 151. As a typical electrode
having a passivating film, iron shows the requisite nonmonotonic course in its current-potential characteristic. The
Fe/HNO3 model can be used t o simulate the most varied
biological excitation phenomena 161. In all other cases a nonmonotonic characteristic of the system is found t o be significant. Doubtless, occurrence of such characteristics is not
confined to the particular set, “current-potential”. On the
contrary, excitable systems are to be expected whenever a
146
High polymers are formed by condensation, in nucleophilic
reactions, of polycyclic aromatic hydrocarbons 111 with
aldoses in liquid H F at room temperature. The site of substitution can be determined by condensation with [1-14C]-~glucose and oxidation to carboxylic acids. Carbazole gives a
polymer-homologous series of condensation products; C-C
bonds occur in all of these, and the OH groups of the sugar
residue can be acetylated.
Being aromatic systems, coals of various ages also give
condensation products (labeling with [l-14C]-~-glucose;
glycosidically bound D-glucose is removed by hydrolysis) 121.
Moreover, very pure graphite (99.999 % of C) condenses with
formation of covalent bonds (0.6-1.8 % of [ I - ~ ~ C I - D - ~ ~ U cose) (31. All the condensation products are free from watersoluble self-condensation products of D-glucose. Benzene and
[1-14C]-~-glucoseafford, amongst other condensation products, triphenylmethane whose labeled tertiary C atom is
derived from the D-glucose (yield: 15 %, calc. on D-glucose).
Toluene and [l-“T]-~-glucoseyield, as well as a methylanthracene, a hydrocarbon C24H24, [ a ]=~-44 ’(in benzene),
which fluoresces blue in solution and contains aliphatic
groups (yield: ca. 4 %, calc. o n D-glucose).
Lecture at Clausthal-Zellerfeld (Germany), on October 27, 1967
[VB 106 IE]
German version: Angew. Chem. 80, 156 (1968)
[ * ] Prof. Dr. F. Micheel
Organisch-Chemisches Institut der Universitat
44 Munster, Hindenburgplatz 55 (Germany)
[l] F. Micheel and L . Rensmann, Makromolekulare Chem. 65, 26
(1963); A . H . Haines and F. Micheel, ibid. 80, 7 4 (1964); F. Micheel and H . Licht, Tetrahedron Letters 1965, 3701; Makromolekulare Chem. 103, 91 (1967).
[Z] F. Micheel and D.Laus, Brennstoff-Chem. 47, 345 (1966).
131 F. Micheel, Lecture at the International Symposium on
Carbohydrate Chemistry, Kingston (Ontario), July 1967; Lecture at Osaka o n October 13, 1967.
Individual Steps in the Chemisorption of Gases on
Metals
By W . M . H. Sachtler[*l
The chemisorption of gases on metals is determined primarily,
not by the collective parameters of the metallic state Fermi level, holes in the d-band, e f c . - but by the chemical
Angew. Chem. internat. Edif. Vol. 7 (1968)
No. 2
properties of the individual surface atoms and by those of the
atoms of the gaseous molecule. Just as in complex chemistry,
the chemical properties of a n adsorbing atom are modified
by its neighbors. A study has been made of the role played
in chemisorption by the geometry ( e . g . the size of the adsorbed atoms, number of adsorption sites on the surface) i n
comparison with the stoichiometry, i.e. the number of
valence electrons of the surface atoms.
Chemisorption of gases of the type H,X on pure G e or Si
surfaces follows stoichiometric laws “1; each molecule dissociates into (I H atoms and one X atom, each H atom saturates
one surface atom, and each X atom saturates a surface
atoms; thus, in sum, 2n surface atoms are saturated per H,X
molecule. The surface atoms behave as univalent species,
since of each four valence electrons of each G e atom three
electrons are used for covalent bonding to the three nearest
neighbors; the fourth electron is available for chemisorption,
as a “dangling bond”.
Stoichiometry also determines chemisorption by typical
metals. However, in contrast to covalent crystals (such as Ge)
metals d o not confine themselves to the “dangling bonds”;
instead, all the valence electrons are available for bonding
with the adsorbate.
As a result chemisorption causes marked demetalization of
the surface atoms and is therefore dissociative in two respects:
the bonds within the gas molecule and also those within the
surface can be broken. By using the field ion microscope
it has been shownr21 that the surface atoms can even leave
their original positions in the lattice and move to more
favorable positions between or even above the adsorbate
atoms. Such rearrangements can occur even at the temperature of liquid nitrogen. Since each atom that leaves
its position in the lattice leaves a vacancy, which can then
move into the interior of the crystal, the injection of vacancies
caused by chemisorption is a n additional phenonemon which
has been verified experimentally.
Chemisorption often occurs in three successive stages:
1 . Chemi-adsorption (surface atoms remain in their original
places in the lattice).
2. Corrosive chemisorption (rearrangement of the atoms of
the surface and of the adsorbate).
3. Ligand chemisorption (the metal atoms or ions that have
migrated in process (2) complete their coordination number
in diffusion-controlled reactions between an excited and an
unexcited molecule with an enthalpy of formation ( - A H ) of
several kcal ‘mole; at higher temperatures this enthalpy can be
measured from the temperature-dependance of the relative
fluorescence intensities, if back-reaction occurs.
The wave number of the maximum of the complex emission
is governed by the simple energy relationship:
where IPD is the ionization energy of the donor molecules,
EAA is the electron affinity of the acceptor molecules, C + U
is the Coulomb + resonance energy in the complex, HF!;b+
is the solvation energy of the complex and Erep is the repulsion energy between A and D in the ground state of the
complex. The validity of this relation has been tested for a
large number of acceptor-donor systems by using substituted
and unsubstituted aromatic compounds and numerous solvents; this work confirms the assumptions made about the
charge-transfer character of the excited molecular complexes.
Moreover, it now becomes possible to estimate the resonance
energy U , which can be ascribed to participation of localized
excited structures
i D
tt
A-D-
t-t
A6
in the complex.
In the system naphthalene (D)/p-dicyanobenzene (A) at high
concentrations, formation of excited triple complexes
(DD)+A- can be observed, which dissociate partly when the
temperature is increased, yielding D and D+A- (excited).
The significance of these studies lies on the one hand in the
possibility of studying the diffusion-controlled kinetics of
molecular complex formation in relation to various parameters {solvent, temperature, pressure, etc.), and o n the
other in the fact that the heteroexcimers, which are readily
detected by means of their characteristic properties, can
appear as intermediates in redox reactions.
Lecture at Braunschweig (Germany), on November 6, 1967 IVB 108 1El
German version: Angew. Chem. 80. 156 (1968)
[*] Prof. Dr. A. Weller
Max-Planck-Institut fur Spektroskopie
34 Gottingen, Bunsenstr. 10 (Germany)
by further chemisorption).
Lecture at Berlin (Germany), on November 3, 1967
[VB 107 IE]
German version: Angew. Chem. 80, 155 (1968)
Fine Structure of Ruthenium(m) Bromide
~-
[*I Prof. Dr. W. M.
H. Sachtler
Koninklijke/Shell-Laboratorium,Amsterdam
Badhuisweg 3, Amsterdam (Netherlands)
111 A. H . Eoonstra, Dissertation, TH Eindhoven, 1967.
121 A . A . Holscher and W. M . H . Sachtler, Discuss. Faraday
SOC.41, 29 (1966).
Formation and Properties of Molecular Complexes
in the Excited State
By A . Welter[*]
The fluorescence spectrum of a solution that contains electron-acceptor (A) as well as electron-donor molecules (D)
can disclose the formation of excited charge-transfer complexes A-D+ (heteroexcimers) by the appearance of a longwave fluorescence emission that is structureless and unaccompanied by a corresponding change in the absorption
spectrum. The molecular complexes, which are unstable in
the ground state, are formed in accord with
A+D
+ A-D+orC+A
+ D+A-
Angew. Chem. internaf. Ea’if.1 VoL 7 (1968) / No. 2
By K . Brodersen [*I
Dii)
RuBr3 crystals are rhombic (space group
121 and not, as
hitherto assumed [I], hexagonal with the Ti13 structure (space
The unit cell (a = 6.47 A, b = 11.205 A, c =
group &).
5.855 A) contains 4 formula units (DX-ray = 5.34 g c m 3 ;
DPYcn.= 5.42 g cm-3).
X-ray determination of the structure by Patterson and Fourier
syntheses (refinement of the parameters by the method of
least squares) shows characteristic (RuzBr3)Br6/2 groups as
the structural unit with the Ru atoms in an approximately
octahedral environment. The points in space group D: are
occupied as follows:
4 R u in 4 (e) with x = 0.2545 and z = 0.01 65
4 BrI in 4 (f) with x = 0.587 and y = 0.599
4 BrII in 4 (f) with x = 0.089 and y = 0.4055
2 BrIII in 2 (a) with x = 0.571
2 BrIv in 2 (b) with x = 0.945
The magnetic moment is much depressed (to zmol= 108r
10 -6 at 20 “ C , temperature-independent) by the formation of
RUZgroups. The interatomic distances are: Ru-Ru = 2.73 8,
(shortest distance between two Ru2 pairs in the chain = 3.12
147
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