Molecular Clusters

A Bridge to SolidState Chemistry. ByThomas P. Fehlner,Jean-Fran�ois Halet,and Jean-Yves Sail-lard. CambridgeUniversity Press,Cambridge 2007.390 pp., hardcover$ 138.00.—ISBN978-0-52185-236-4

A professor is talking to his students; hewants to give them an understanding ofthe modern approach to inorganicchemistry, which conceptually integratesthe electronic situation of molecules,clusters and solids. The reader of thistextbook soon realises that it is one halfof an intensive dialogue. The other halfis no less present—you can just aboutsee the faces of the students living thisscript and anticipate their questions.

Three authors well-known in theworld of molecules, who have each ofthem built bridges to solid state chemis-try, take up the enormous challenge ofdelivering a widely applicable descrip-tion of chemical bonding in a generallycomprehensible manner. This bookcomprises eight chapters and an appen-dix, and the text is rife with questions,tasks and exercises of all kinds, which donot admit of a passive reader or listener.T. P. Fehlner, J.-F. Halet and J.-Y. Sail-lard use concepts which are accepted inmolecular chemistry and apply them tosections of solids. Almost in passing theyundertake to satisfy the needs of“researchers from the wide field ofnanochemistry”, given that a nanoparti-cle is but a large cluster or a small solid(to which, unfortunately, the description

of a molecule or a solid does notnecessarily apply).

A tall order, then, which isapproached with all due care. Nothingis better suited to illustrate this chal-lenge than an attempt at summarizingthe first chapter (“Introduction”): asmay be expected, it starts with molec-ular orbitals and the H2 molecule, butafter only four pages the reader (under-graduates and graduates) is asked tosketch his own MO description using theeigenvalues (presented in the form of atable) of a hypothetical B2 molecule. Healso makes acquaintance with Mullikenoverlap populations, frontier orbitalsand MO diagrams for polyatomic mol-ecules. For the application of Hoff-mann3s fragment approach when deal-ing with molecules such as P3H5, he isreferred to the appendix (“if neces-sary”). I can well imagine that manyreaders will find it necessary to consultthe appendix! It is in the introduction,too, that we learn the qualitative repre-sentation of MO diagrams of coordina-tion bonds such as Cr(CO)6, [Co-(NH3)6]3+, and—in an exercise for thereader—how to handle coordinationcompounds with C2H4 as a ligand. Notonly is multi-centre bonding, too, intro-duced (the example chosen being dibor-ane), but rules for electron counting arepresented, Jahn-Teller instabilities arementioned, and the reader quickly prac-tises the discussion of the eight-electronrule on hypervalent xenon difluoride.The introduction ends with a sectionentitled “Why count ?”. I leave it to thereaders of this review—who I hope haveworked up an appetite for more—to findout the answer.

Chapter 2 is dedicated to main groupelement clusters. Adamantane, R4Ge4,R4Ga4, and B4Cl4 are briefly touchedupon before “deltahedra” become thesubject of discussion. The bonding-the-oretical description of closo-hydrobo-rates, nido-, and arachno-boranes isthorough and at the same time verydense; the authors3 great familiaritywith the subject matter is evident. Thischapter alone justifies a recommenda-tion of the book to all students, nomatter of what year. It closes the gapbetween the common textbooks of inor-ganic chemistry, which, e.g., leave theuses of the Wade rules (often introducedin a perfunctory manner) in the dark for

many, and research literature, which isnot necessarily ever referred to by manystudents. All this, however, is againtreated at great speed, and towards theend of the chapter, the authors go intogreater detail than would seem neces-sary. The last sub-chapter, on the otherhand, is brief: the successful transfer of“Wade counting”, practised on closo-hydroborates, to the structure of ele-mental a-rhombohedral boron is usuallythe part which most fascinates thosewho have been able to follow the lecture(or the chapter)—that which gives themsudden insight. Fehlner et al. just give afew lines to this example and refer thereader to the appendix. At this point Iwould have wished for a more enthusi-astic reference to the book3s title, thebridge to solids.

The third chapter centres on transi-tion metal clusters. Facts and conceptsare presented in a similarly concisemanner as what went before, and againthere are numerous exercises to test thereader. Towards the end of the chapter,the authors use quasi-elemental, verylarge clusters to pave the way to nano-scale particles. This sub-chapter gives agood first idea of the problems specificto nano particles (influence of the sur-face, methods of characterisation, etc.)and introduces important key conceptsand literature.

Main group and transition metalchemistry can be combined. Chapters 4and 5 describe different approaches tothe bonding-theoretical treatment ofwell-known as well as rare bonds. Theguiding thread is the repeated crossingof the border between classic transitionmetal and cluster chemistry. Seeminglycompeting approaches are put into rela-tion and used to give as broad aspossible a view of inorganic molecularchemistry.

The impatiently awaited “transitionto the solid state” finally follows inchapter 6. The point of departure chosenis [Al69R18]3�, and the titillating questionat which point a particle consisting ofmetal atoms becomes a metal is touchedupon. It is concealed in the discussion ofwhether it is the surface or the so-called“bulk” which determines the properties.Is the energy of such particles differentfor different geometrical forms ? At thispoint the authors put in a brief tutorialon “sphere packing (ccp and hcp) and

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8774 * 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2008, 47, 8774 – 8775

their holes” and “periodicity”, whichmight have been better placed in theappendix. The following leap in com-plexity to HCckel calculations, bandstructures, densities of states, COOPs,etc. is enormous—a welcome re-encounter for those who grew up withRoald Hoffmann3s A Chemist�s View ofBonding in Extended Structures, butperhaps something of a challenge tothe above-mentioned undergraduates.The latter, however, will find the effortworth their while when at the end of thechapter they are not only able to read,but to understand the discussion of thedensity of states diagrams of aluminium,nickel, graphite, and diamond. The onlything which seems to make not too muchsense in this context is the sub-chapteron “complex periodic units”.

Examples follow in chapter 7, whichillustrates the way from the molecule tothe extended solid. Interstitial carbonatoms in complexes and metal carbides

are discussed. Closo-hydroborates,which were introduced earlier on, arecompared with polyhedral units inboron-rich compounds. Further pointsof great interest are fullerene/carbonnanotubes, ternary hydrides = hydridemetallates (the description of the CaF2

structure, in which half of the tetrahe-dral holes of a ccp Ca package remainunoccupied by accident, is a bit irritatingin this context) and clusters in Chevrelphases. The latter are discussed as ruleviolators—why this is so, you are invitedto find out for yourself by reading thebook.

Chapter 8 is different from the rest.We are no longer dealing with theconceptual description of the electronicsituation of atomic bonds; the authorsnow turn to making suggestions for thesynthesis of new solid phases on thebasis of molecular precursors. Here, too,the reader will find many interestingexamples, which in this combination

must surely be unique in a textbook.Boron carbide (which, however, is struc-turally derived not from b-, but from a-rhombohedral boron) and metallicglasses on a Fe–B basis are extraordi-narily attractive systems theoretically,synthetically, and with respect to mate-rials science, and there is no othertextbook of inorganic chemistry whichtreats them in this way. A fine, relativelyaccessible end to an intellectually chal-lenging book which—according to theauthors—was written for students but inwhich all of us may find points ofinterest and which bridges the gapfrom the molecule to the solid.

Barbara AlbertEduard-Zintl-Institut f6r Anorganischeund Physikalische Chemie, TechnischeUniversit9t Darmstadt (Germany)

DOI: 10.1002/anie.200785625

AngewandteChemie

8775Angew. Chem. Int. Ed. 2008, 47, 8774 – 8775 * 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.angewandte.org