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Book Review Icons and Symmetries. By S. L. Altmann

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Super-Acids and Acidic Melts as Inorganic
Chemical Reaction Media. By 7: A .
O’DonneN. VCH Verlagsgesellschaft,
Weinheim/VCH
Publishers,
New
York. 1993. XI. 243 pp.. hardcover
D M 184.00.--ISBN 3-527-28092-8/156081-035-1
There have been a number of monographs on this subject area, most recently
the book Superucick, by Olah, Surga
Prakash. and Somnier. which appeared in
1985 and dealt mainly with the protonation of organic molecules. The latter topic
is therefore not treated in the book reviewed here.
After giving the essential definitions of
acids and bases and an introduction to the
chemistry of aqueous solvent media, the
author compares different methods for investigating dissociation in superacids and
establishing a scale of acidity. This is followed by a description of the most
commonly used acidic solvents, H,SO,,
CF,SO,H, and F S 0 , H ; in accordance
with their importance, considerable space
is devoted to hydrogen fluoride and its
mixtures with Lewis acids. The part on
specific substances covers a wide range,
extending from the homonuclear cations
of halogens, chalcogens, and metals,
through transition element cations in both
normal and lower oxidation states, to zintl,
polychalcogen, and polyhalogen anions.
The author points out that the various
ions described have certain common
properties, insofar as polycations can only
exist in superacids and acidic melts,
whereas polyanions can be formed in basic solvents. This general ordering principle accounts for various observations.
Since B r i and Br: are only formed in
extremely strong superacids with H, values of about - 19 and - 15 respectively,
the still significantly electrophilic species
Cl: cannot be isolated as a substance. The
example of 1: discussed on pages 109 and
219 provides impressive confirmation
that, in addition to the absolute acidity,
the individual Drouerties of the solvent
play an important role in stabilization.
The fact that bases catalyze the disproportionation of polycations is regarded as
highly significant. The author cites many
examples of this behavior, which is observed both in superacids and in chloroaluminate melts when their basicity is increased. Aspects of the chemistry in salt
melts are also discussed at length, with
special attention to the similarities and
differences compared with superacids.
This book is well worth reading, not
only for its systematic treatment but also
for the valuable practical hints on working with these very difficult solvents. For
I
-
example, how many chemists already
know all the factors that must be observed
in order to achieve the record value
H , = - 21 in HFjSbF,?
The subject matter is clearly arranged,
and the individual chapters can be read
independently of each other. Many crossreferences are given, so that one can work
through the material quite rapidly. A less
satisfactory aspect is that. apart from his
own publications. the author relies mainly
on the reviews by Gillespie. Passmore.
Corbett, Mamantov, and others, while neglecting the primary literature, especially
the most recent work. Consequently the
book is not very up-to-date. However, despite some shortcomings in matters of detail it can be recommended unreservedly
for advanced students.
Rolf Minkwitz
Fachbereich Anorganische Chemie
der Universitit Dortmund (FRG)
Icons and Symmetries. By S. L. AItmunn.
Oxford University Press, Oxford, 1992.
VIII. 104 pp., hardcover f 14.95.-ISBN
0-19-855 599-7
The subject of symmetries and their
mathematical description using group theory is a popular one for book authors. It
has become difficult even to keep track of
the number of textbooks written specifically for chemists. Simon Altmann has already published several monographs and
textbooks on the subject. all of which introduce novel aspects, both in content and
form of presentation.
Thus, one opens this slim book with
great curiosity, and is not disappointed.
Treating the subject at a mathematical level
accessible to most readers, Altmann uses
three case studies, taken from his lectures
in the Science Faculty of the Catholic
University of Leuven, to explore the relationships between physical objects, models, and symbols (“icons”). Although he
cites Hermann Weyl’s well-known book
Symmetry as the model for these lectures,
Altmann wisely decides on a different,
quite original, approach. He discusses the
formulation of the physical problem handin-hand with the historical and philosophical aspects, with the aim of showing how
ideas of symmetry have entered into our
scientific thinking. Thus, the book is concerned with discussing symmetry in a general way rather than with formally describing it by group theory, and accordingly the term “group” is not even mentioned.
The three examples can be roughly classified as belonging respectively to physics,
mathematics. and chemistry. In the first
the author discusses the concept of symmetry from the standpoint of Oersted’s paradox concerning the interaction between a
compass needle and an electric current.
This involves mirror image symmetry-to
be more precise, the transformation
properties of vectors on reflection. Altmann compares different formulations of
the symmetry principle by Archimedes,
Thomas Aquinas, and Pierre Curie
(”Lorsque certaines causes produisent
certains effets, les elements de symmetrie
doivent se retrouver dans les effets
produits”). [Since definite causes produce
definite effects, the elements of symmetry
must be deduced from the effects that they
produce.] He shows very convincingly the
sort of confusion that can arise if one
applies symmetry uncritically to analyze a
physical problem and equates the properties of a symbol such as a vector arrow
with those of the physical entity that it
represents. Nowadays we are all familiar
with the need to distinguish between polar
and axial vectors.
tn the second example Altmann discusses the relationship between quaternions
and rotations, which he treated in detail a
few years ago in a monograph devoted to
the topic. He relates the fascinating history
of quaternions as an example of how even
such a clever intellect as that of Hamilton,
the inventor of quaternions. could be led
astray through a wrong choice of an
“ E I K ~ V ” . In a conclusive analysis Altmann shows how this error, which influenced later developments over a long period, was related to Hamilton’s particular
philosophical view of nature. Hamilton
arrived at the idea of quaternions by an
algebraic route while attempting to further generalize complex numbers. Altmann contrasts Hamilton’s approach
with that of Rodrigues, who, independently and at almost the same time, developed a theory of rotations from a geometrical standpoint. The chapter ends with a
rigorous and detailed consideration of the
transformation properties of vectors, with
a look also at tensors and spinors and
their symmetry properties.
In the third chapter the author discusses the use of symmetry considerations to
classify the energy levels of atoms and
solids. He bases the latter on a version of
the band structure theory of solids reduced to its minimum essentials, that of a
linear chain. Next he discusses the problem of symmetry breaking, taking as an
example the Peierls instability of polyacetylene. Here again a paradox only arises if one too hastily equates the symmetry
of the model with that of the real physical
situation. However, as the author himself
points out, the reader needs to be more
adept at formal reasoning here than in the
rest of the book, in order to follow the
proof given here for the degeneracy of
states at the boundaries of the Brillouin
zone in a quasilinear chain as a consequence of the presence of a glide plane.
Nevertheless, it is difficult to see why the
author. despite his insistence on care in
the choice of symbols, does not use two
orbital representations of the corresponding Bloch functions. which would have
immediately convinced any chemist that a
degeneracy exists.
This book contains many ideas to stimulate the reader to think about symmetry
and its effects as they relate to describing
nature. The historical perspectives undoubtedly help here. although occasionally
these are presented in a way that the reader may find trying. Sometimes one has the
impression that extra details are included
not so much to illuminate the problem as
to show off the author’s historical knowledge. At one point (p. 44) it seems that he
is conscious of this himself:
.and thus
you will feel like closing the book. If this
is so, please listen t o my entirely disinterested advice (my royalties are paid to me
even if y o u burn this book) and go on
reading. . .”. This style is perhaps not to
everyone’s taste. It also seems a little
surprising when the author, in the
preface, expresses a wish that young
people might read this book before coming
to university. Despite these comments,
the book can be thoroughly recommended to everyone who wishes to become involved with symmetry and its role in
science.
Notker Risch
Lehrstuhl fur Theoretische Chemie
der Technischen Universitat Miinchen
Garching ( F R G )
‘ I . .
Charge Transfer Photochemistry of Coordination Compounds. By 0. Horvuth and
K. L. Stcvenson. VCH Publishers, New
Yor k jVC H Verl agsgesellsch aft, Weinheim,
1993. XVITT, 380 pp., hardcover $98.00,
D M 238.00.-ISBN I -56081-564-7/3-52789 564-7
It is now almost a quarter of a century
since Balzani and Carassiti, in their classic
work Piiotoclieniistry of Coordination
Cornpounds (Academic Press, 1970), presented the last comprehensive picture of
the subject. In the monograph reviewed
here, 0. Horvith and K. L. Stevenson set
out to bridge this gap in time for an important part of that subject, namely charge
transfer photochemistry. Their treatment
is mainly concerned with photoreactions
in which the primary step is a charge transfer process involving light excitation of a
Werner type metal complex in homogeneous solution. The book also briefly covers some photoredox reactions of such
complexes in the solid state or in microheterogeneous systems. The restriction of
the coverage of the photochemistry of
organometallic compounds, which is stated in the preface, is only departed from
significantly in the treatment of rhenium
complexes.
The book is divided into two parts, with
thirteen chapters altogether. The first part
consists of three chapters which deal, mainly in a condensed form, with the basic principles of the spectroscopy, photochemistry,
and photophysics of coordination compounds. The second part covers in detail
the results published up to the beginning
of 1991 on the charge transfer photochemistry of the complexes, arranged according
to the group of the Periodic Table to which
the central atom belongs. Here the authors
have sensibly devoted most attention to
the photochemistry of the Main Group
metals, previously only rather scantily
covered in monographs, while presenting
in condensed form the photochemistry
of ruthenium(I1)-polypyridyl complexes,
which has already been very adequately
reviewed elsewhere. To make the work as
up-to-date as possible there is a bibliographic appendix listing publications that
appeared in the period 1990-1992 and
could not be reviewed in the individual
chapters. A further appendix explains the
abbreviations and symbols used. and the
volume is completed by formula and keyword indexes.
The exhaustive coverage of experimental
results makes this book a mine of information for the professional photochemist.
On the other hand, it is doubtful whether
the authors have succeeded in their declared aim of presenting the subject in an
attractive way to many potential newcomers. There are three main reasons for this.
Firstly, the concentration on experimental
results has meant that many fascinating
applications of charge transfer photochemistry, such as solar energy conversion, information processing, o r the generation of
catalytically active species for organic synthesis, have had to be virtually ignored.
Secondly, the arrangement of the complexes according to which group of the
Periodic Table the central atom belongs to
creates a problem, as it means that generalizations within individual chapters are
rarely possible. since the direction of the
photoinduced charge transfer, and therefore the subsequent reaction steps, are
greatly dependent on the oxidation state
of the central atom and the nature of the
ligands. The authors have tried to take this
into account by dividing the chapters into
subsections for different oxidation states
of the central atom and by including many
cross-references. However, it is hard to understand why the further subdivision according to coordination pattern that has
been used in the text is not indicated in the
list of contents. Thirdly, it would have
been desirable to have a summary classifying the reactions according to broad
types.
Regrettably, the reader is often confused by the inconsistent use of terms and
symbols, and by the many printing errors
which in some cases alter the meaning.
For example, the quantum yield is represented by the symbol I7 in the introduction and in the list of abbreviations and
symbols, whereas in the main text the
more usual symbol @ is used. The neutral
complex [Co(gly),] is shown in the formula
index, and sometimes also in the text, with
a triple positive charge. The acetate ion in
Equation 9.123 is shown as retaining its
negative charge even after oxidation. In
the text accompanying Equation 12.29
reference is made to a ring-opening with
cleavage of a C o - C bond, whereas the
formula diagram shows cleavage of the
Co-N bond. In the classification of charge
transfer transitions in Chapter 3 the expression ’ion pair charge transfer’ (IPCT)
is not mentioned, despite the fact that it is
used frequently, even incorrectly in a few
cases (pp. 94, 163). Lastly a word about
the presentation: in the illustrations to the
chapters of the second part the authors
have gone to the trouble of converting the
formula diagrams and spectra copied from
the original papers into a uniform style;
however, the result is not altogether convincing when compared with the quality
of the figures in the first part.
Notwithstanding these critical comments, the book is likely to be very well
received by both coordination chemists
and photochemists. The former will learn
how light can serve as a reagent by interacting with their compounds in ways that
may be new to them, while the latter will
appreciate having easy access to a large
collection of factual material. Therefore,
despite the high price it deserves a place in
every chemical library.
Rolund Billing
Fachbereich Chemie
der Universitat Leipzig (FRG)
Organic Photochemistry: A Visual Approach. By .
I
Kopeck?:. VCH Publishers,
New YorkiVCH Verlagsgesellschaft,
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