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Molecular Clusters. A Bridge to Solid State Chemistry. By ThomasP

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Molecular Clusters
A Bridge to Solid
State Chemistry. By
Thomas P. Fehlner,
Jean-Franois Halet,
and Jean-Yves Saillard. Cambridge
University Press,
Cambridge 2007.
390 pp., hardcover
$ 138.00.—ISBN
978-0-52185-236-4
A professor is talking to his students; he
wants to give them an understanding of
the modern approach to inorganic
chemistry, which conceptually integrates
the electronic situation of molecules,
clusters and solids. The reader of this
textbook soon realises that it is one half
of an intensive dialogue. The other half
is no less present—you can just about
see the faces of the students living this
script and anticipate their questions.
Three authors well-known in the
world of molecules, who have each of
them built bridges to solid state chemistry, take up the enormous challenge of
delivering a widely applicable description of chemical bonding in a generally
comprehensible manner. This book
comprises eight chapters and an appendix, and the text is rife with questions,
tasks and exercises of all kinds, which do
not admit of a passive reader or listener.
T. P. Fehlner, J.-F. Halet and J.-Y. Saillard use concepts which are accepted in
molecular chemistry and apply them to
sections of solids. Almost in passing they
undertake to satisfy the needs of
“researchers from the wide field of
nanochemistry”, given that a nanoparticle is but a large cluster or a small solid
(to which, unfortunately, the description
8774
of a molecule or a solid does not
necessarily apply).
A tall order, then, which is
approached with all due care. Nothing
is better suited to illustrate this challenge than an attempt at summarizing
the first chapter (“Introduction”): as
may be expected, it starts with molecular orbitals and the H2 molecule, but
after only four pages the reader (undergraduates and graduates) is asked to
sketch his own MO description using the
eigenvalues (presented in the form of a
table) of a hypothetical B2 molecule. He
also makes acquaintance with Mulliken
overlap populations, frontier orbitals
and MO diagrams for polyatomic molecules. For the application of Hoffmann3s fragment approach when dealing with molecules such as P3H5, he is
referred to the appendix (“if necessary”). I can well imagine that many
readers will find it necessary to consult
the appendix! It is in the introduction,
too, that we learn the qualitative representation of MO diagrams of coordination bonds such as Cr(CO)6, [Co(NH3)6]3+, and—in an exercise for the
reader—how to handle coordination
compounds with C2H4 as a ligand. Not
only is multi-centre bonding, too, introduced (the example chosen being diborane), but rules for electron counting are
presented, Jahn-Teller instabilities are
mentioned, and the reader quickly practises the discussion of the eight-electron
rule on hypervalent xenon difluoride.
The introduction ends with a section
entitled “Why count ?”. I leave it to the
readers of this review—who I hope have
worked up an appetite for more—to find
out the answer.
Chapter 2 is dedicated to main group
element clusters. Adamantane, R4Ge4,
R4Ga4, and B4Cl4 are briefly touched
upon before “deltahedra” become the
subject of discussion. The bonding-theoretical description of closo-hydroborates, nido-, and arachno-boranes is
thorough and at the same time very
dense; the authors3 great familiarity
with the subject matter is evident. This
chapter alone justifies a recommendation of the book to all students, no
matter of what year. It closes the gap
between the common textbooks of inorganic chemistry, which, e.g., leave the
uses of the Wade rules (often introduced
in a perfunctory manner) in the dark for
* 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
many, and research literature, which is
not necessarily ever referred to by many
students. All this, however, is again
treated at great speed, and towards the
end of the chapter, the authors go into
greater detail than would seem necessary. The last sub-chapter, on the other
hand, is brief: the successful transfer of
“Wade counting”, practised on closohydroborates, to the structure of elemental a-rhombohedral boron is usually
the part which most fascinates those
who have been able to follow the lecture
(or the chapter)—that which gives them
sudden insight. Fehlner et al. just give a
few lines to this example and refer the
reader to the appendix. At this point I
would have wished for a more enthusiastic reference to the book3s title, the
bridge to solids.
The third chapter centres on transition metal clusters. Facts and concepts
are presented in a similarly concise
manner as what went before, and again
there are numerous exercises to test the
reader. Towards the end of the chapter,
the authors use quasi-elemental, very
large clusters to pave the way to nanoscale particles. This sub-chapter gives a
good first idea of the problems specific
to nano particles (influence of the surface, methods of characterisation, etc.)
and introduces important key concepts
and literature.
Main group and transition metal
chemistry can be combined. Chapters 4
and 5 describe different approaches to
the bonding-theoretical treatment of
well-known as well as rare bonds. The
guiding thread is the repeated crossing
of the border between classic transition
metal and cluster chemistry. Seemingly
competing approaches are put into relation and used to give as broad as
possible a view of inorganic molecular
chemistry.
The impatiently awaited “transition
to the solid state” finally follows in
chapter 6. The point of departure chosen
is [Al69R18]3 , and the titillating question
at which point a particle consisting of
metal atoms becomes a metal is touched
upon. It is concealed in the discussion of
whether it is the surface or the so-called
“bulk” which determines the properties.
Is the energy of such particles different
for different geometrical forms ? At this
point the authors put in a brief tutorial
on “sphere packing (ccp and hcp) and
Angew. Chem. Int. Ed. 2008, 47, 8774 – 8775
Angewandte
Chemie
their holes” and “periodicity”, which
might have been better placed in the
appendix. The following leap in complexity to HCckel calculations, band
structures, densities of states, COOPs,
etc. is enormous—a welcome reencounter for those who grew up with
Roald Hoffmann3s A Chemists View of
Bonding in Extended Structures, but
perhaps something of a challenge to
the above-mentioned undergraduates.
The latter, however, will find the effort
worth their while when at the end of the
chapter they are not only able to read,
but to understand the discussion of the
density of states diagrams of aluminium,
nickel, graphite, and diamond. The only
thing which seems to make not too much
sense in this context is the sub-chapter
on “complex periodic units”.
Examples follow in chapter 7, which
illustrates the way from the molecule to
the extended solid. Interstitial carbon
atoms in complexes and metal carbides
Angew. Chem. Int. Ed. 2008, 47, 8774 – 8775
are discussed. Closo-hydroborates,
which were introduced earlier on, are
compared with polyhedral units in
boron-rich compounds. Further points
of great interest are fullerene/carbon
nanotubes, ternary hydrides = hydride
metallates (the description of the CaF2
structure, in which half of the tetrahedral holes of a ccp Ca package remain
unoccupied by accident, is a bit irritating
in this context) and clusters in Chevrel
phases. The latter are discussed as rule
violators—why this is so, you are invited
to find out for yourself by reading the
book.
Chapter 8 is different from the rest.
We are no longer dealing with the
conceptual description of the electronic
situation of atomic bonds; the authors
now turn to making suggestions for the
synthesis of new solid phases on the
basis of molecular precursors. Here, too,
the reader will find many interesting
examples, which in this combination
must surely be unique in a textbook.
Boron carbide (which, however, is structurally derived not from b-, but from arhombohedral boron) and metallic
glasses on a Fe–B basis are extraordinarily attractive systems theoretically,
synthetically, and with respect to materials science, and there is no other
textbook of inorganic chemistry which
treats them in this way. A fine, relatively
accessible end to an intellectually challenging book which—according to the
authors—was written for students but in
which all of us may find points of
interest and which bridges the gap
from the molecule to the solid.
Barbara Albert
Eduard-Zintl-Institut f6r Anorganische
und Physikalische Chemie, Technische
Universit9t Darmstadt (Germany)
DOI: 10.1002/anie.200785625
* 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
8775
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