Metal complexes play important roles as catalysts or other participants in synthetic and biological reactions. Substrates and sometimes attacking reagents also are activated through coordination with metal atoms or ions. In these events the natures not only of the central metals but also of ancillary ligands exert important influences on the stability and reactivity of the coordinated substrates. A ligand in general can adopt various coordination modes depending on its chemical environment, thus functioning as a probe. The number of coordination modes increases with increasing complexity of the ligand. In this book it is shown that even the simplest mono- and diatomic ligands such as H, CO, and N2 exhibit a variety of coordination modes, which are related to their reactions. The thiocyanate anion is taken up as a representative of the triatomic ambidentate ligands, and factors influencing the preferences for N- und S-bonding are summarized. Coordination chemistry of ss-dicarbonyl compounds is a highlight of this book. Acetylacetone, one of the most familiar Werner ligands, is shown to favor -carbon and n-allylic bonding in many instances. Its versatile behaviour in changing coordination modes is revealed."

Primarily, the aim of this book is to provide a reference work for senior students and research workers engaged in the synthetic aspects of chemistry. The various classes of compounds under discussion provide useful interme diates for the synthesis of numerous nitrogen-containing derivatives. Imidoyl halides are also intermediates in several classical name reactions, such as the Gattermann, Houben-Hoesch, and Vilsmeier-Haack syntheses of aldehydes and ketones, the Beckmann rearrangement, and the v. Braun degradation. Some imidoyl halides have shown interesting agricultural activities, and the generation of highly reactive species (ketenimines, nitrile oxides, nitrile imides, carbodiimides, etc.) from imidoyl halides has contributed to the study of polar cycloaddition reactions. To enable researchers to utilize this chemistry without consulting the original references, I have included a number of selected working examples. This procedure will facilitate the transformation of written information into well designed experiments, especially since part of the cited literature is not readily available. The book is organized around classes of imidoyl halides, with synthesis and chemistry discussed in an orderly fashion. The physical properties of the known imidoyl halides are listed in tables, and I have attempted to draw attention to the more recent literature. The one or two references provided for each compound represent those which best describe its physical constants and synthesis.

Since the early 1930's, Soviet chemists have played a lead ing role in the study of unfamiliar oxidation state compounds of the peroxide, superoxide, and ozonide types. Interest in the alkali and alkaline earth metal derivatives is now widespread and diverse, and numerous practical applications of these com pounds have evolved, ranging from their use as air revitaliza tion materials in space cabins to their use in compounding semiconductor materials. Professor Vol'nov is eminently qualified to write this monograph since for many years he has been a leading investi gator and prolific writer in the field of peroxide, superoxide, and ozonide chemistry. He has succeeded in presenting a lucid and detailed discussion of past work, the present state, and the future potential of this area of unfamiliar oxidation state chemistry. Of particular interest is Professor Vol 'nov's extensive compilation of available thermodynamic, kinetic, and structural data for the alkali and alkaline earth peroxides, superoxides, and ozonides. In addition, he has reviewed the known methods of synthesis, as well as the practical applications for which these compounds are suited. This monograph will be of interest and value to chemists, not only for the information it imparts, but equally for the information it does not impart, thereby illuminating the re search paths and investigation which must be undertaken in order to increase our knowledge concerning the chemistry of this important class of chemical compounds."

In recent years many research workers have turned their attention to the quantitative characterization of complex compounds and reactions of complex-formation in solution. Instability constants characterize quantitatively the equili bria in solutions of complex compounds and are extensively used by chemists of widely-varying specialities, in analytical chemistry, electrochemistry, the technology of non-ferrous and rare metals, etc., for calculations of various kinds. Despite the wealth of numerical data, no reasonably full coliection of instability constants of complex compounds has been made until now. The various individual collections of data are far from complete and in most cases omit references to the source materials. Moreover, the present state of the chemistry of complex compounds most urgently demands the complete systematization of data on instability constants and an extension of work in this field which would take advantage of the latest physico-chemical methods. The present work contains instability constants for 1,381 complex compounds. We have considered it convenient to preface the summary of the instability constants with an introductory section of a general theoretical character. This section deals with methods for the calculation of instability constants from experimental data, the influence of external conditions, such as temperature and ionic strength, on the stability of com plexes, and the principal factors determining the stability of complex compounds in aqueous solution. (vii) PREFACE In compiling the summary we have used the original litera ture and abstracts for the most part up to 1954, and some work published in 1955-1956."

This book is intended to provide a fundamental basis for the study of the interaction of polymers with living systems, biochemicals, and with aqueous solutions. The surface chemistry and physics of polymeric materials is a subject not normally covered to any significant extent in classical surface chemistry textbooks. Many of the assumptions of classical surface chemistry are invalid when applied to polymer surfaces. Surface properties of polymers are important in the development of medical devices and diagnostic products. Surface properties are also of vital importance in fields such as adhesion, paints and coatings, polymer-filler interactions, heterogeneous catalysis, composites, and polymers for energy generation. The book begins with a chapter considering the current sources of information on polymer surface chemistry and physics. It moves on to consider the question of the dynamics of polymer surfaces and the implica tions of polymer surface dynamics on all subsequent characterization and interfacial studies. Two chapters are directed toward the question of model polymers for preparing model surfaces and interfaces. Complete treatments of X-ray photoelectron spectroscopy and attenuated total reflection infrared spectroscopy are given. There is a detailed treatment of the contact angle with particular emphasis on contact angle hysteresis in aqueous systems, followed by chapters on interfacial electrochemistry and interface acid-base charge-transfer properties. The very difficult problem of block and graft copolymer surfaces is also discussed. The problem of theoretical calculations of surface and interfacial tensions is presented. Raman spectroscopy is considered as an analytical technique for polymer surface characterization."

For almost a quarter of a century the words "nuclear magnetic reso nance" were synonymous with proton I, leasurements. During this period the literature abounded with a seemingly infinite variety of 1H NHR studies concerned primarily with carbon chemistry. Occasionally a "novel" nucleus was studied and, even in those early days, the poten- 13 14 31 19 tial offered by C, N, P and F was clearly recognized. Despite the allure, the technical difficulties involved in measuring some of these nuclei were far from trivial. Small magnetic moments and low natural abundance in combination with spin-spin coupling from other nuclei, mostly protons, resulted in a signal-to-noise problem whose severity effectively excluded the study of metal complexes with unfa vorable solubility characteristics. The first important breakthrough came with the advent of broad band 1H-decoupling. For example, the featureless broad 31p resonance associated with the commonly used ligand triphenyl phosphine is converted to a sharp, more readily ob served singlet when wide-band decoupling is employed (see Fig. 1). Despite this improvement investigation of more interesting molecules, such as catalytically active complexes was forced to await the devel opment of Fourier Transform methods since only with relatively rapid signal averaging methods could sufficient signal-to-noise ratios be achieved."

In recent years several improvements have been made in the manufacturing of resistive, superconducting and hybrid mag nets. Condensed matter physicists are nowadays doing ex periments in steady magnetic fields of up to 30 Tesla. But the field homogenity {/B}, required in a volume of the order of a 3 few cm is usually several orders of magnitude less severe than the one which is needed for high resolution NMR. Over the last 30 years, with each generation of new high resolution NMR spectrometers, from 100 MHz up to 600 MHz, taking advan tage of the increase in sensitivity and resolution, new areas of research have been opened in chemistry, physical chemistry and biochemistry. The generation of the 20 Tesla supercon ducting magnets is coming. Thus one may seriously start to consider high resolution NMR at 1 GHz. The purpose of this volume is to examine some of the advantages which can be obtained at such high frequencies and some of the problems we shall be facing. An important aspect of NMR at high field which is not presented in this volume concerns the design of the magnet. The building of a superconducting magnet, producing a field 10 3 higher than 20 T, with a field homogeneity IlB/B 10-, in a cm volume still remains today in 1990 a major challenge. Grenoble, France J. B. Robert Guest-Editor Professor J. B. Robert Service National des Champs Intenses B. P."

The upsurge in development of homogeneous catalysis in both aca- demic and industrial areas has prompted us to organize the Second Interna- tional Workshop at Shiga, Japan, 1977. The objective of this workshop was similar to that of the first: to identify opportunities for the solution of energy problems and industrial production problems by homogeneous catalysis. This workshop on homogeneous catalysis was sponsored by the Toray Science Foundation, the Yoshida Foundation for Science and Technology, the Yamada Science Foundation, and the National Science Foundation. The Robert A. Welch Foundation Grant A-420 partially supported the time spent by M. Tsutsui for the organization of the workshop and the edi- torial work of these proceedings. Organizing Committee, April, 1978 Jack Halpern (U.S.A.) Yoshio Ishii Oapan) Jiro Tsuji Oapan) Minoru Tsutsui (U.S.A.) Akio Yamamoto Oapan) v Contents Metal Clusters in Catalysis XVII: Catalytic Hydrocarbon Reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 E.L. Muetterties Cluster Catalysis: Homogeneous Catalytic Oxidation of Carbon Monoxide and of Ketones with Molecular Oxygen Using Complexes of Rhodium(O), Iridium(I), and Platinum(O). . . . . . 11 D.M. Roundhill Metal Carbonyl Catalysis of Carbon Monoxide Reactions. . . . . . . . . . 25 . R.B. King, A.D. King, Jr., M.Z. Iqbal, C.C. Frazer and R.M. Hanes Activation of Saturated Hydrocarbons by Ruthenium(I) Complexes? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 . . . . . . . . . . Brian R. James and Daniel K.W. Wang Oxidative Addition to Metal Atoms: Mechanism, Use of Resultant Reactive RMX and R2M Species in Homogeneous Catalysis Processes and Metal Atom-Alkane Interactions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 . . . . . . . . . .

As natural minerals, silica and silicates constitute by far the largest part of the earth's crust and mantle. They are equally important as raw materials and as mass produced items. For this reason they have been the subject of scientific research by geoscientists as well as by applied scientists in cement, ceramic, glass, and other industries. Moreover, intensive fun damental research on silicates has been carried out for many years because silicates are, due to their enormous variability, ideally suited for the study of general chemical and crystallographic principles. Several excellent books on mineralogy and cement, ceramics, glass, etc. give brief, usually descriptive synopses of the structure of silicates, but do not contain detailed discussions of their structural chemistry. A number of monographs on special groups of silicates, such as the micas and clay min erals, amphiboles, feldspars, and zeolites have been published which con tain more crystal chemical information. However, no modern text has been published which is devoted to the structural chemistry of silicates as a whole. Within the last 2 decades experimental and theoretical methods have been so much improved to the extent that not only have a large number of silicate structures been accurately determined, but also a better under standing has been obtained of the correlation between the chemical composition of a silicate and its structure. Therefore, the time has been reached when a modern review of the structural chemistry of silicates has become necessary."

Low dimensionality is a multifarious concept which applies to very diversified materials. Thus, examples of low-dimensional systems are structures with one or several layers, single lines or patterns of lines, and small clusters isolated or dispersed in solid systems. Such low dimensional features can be produced in a wide variety of materials systems with a broad spectrum of scientific and practical interests. These features, in turn, induce specific properties and, particularly, specific transport properties. In the case of zeolites, low dimensionality appears in the network of small-diameter pores of molecular size, extending in one, two or three di mensions, that these solids exhibit as a characteristic feature and which explains the term of "molecular sieves" currently used to name these ma terials. Indeed, a large number of industrial processes for separation of gases and liquids, and for catalysis are based upon the use of this low dimensional feature in zeolites. For instance, zeolites constitute the first class of catalysts employed allover the world. Because of the peculiarity and flexibility of their structure (and composition), zeolites can be adapted to suit many specific and diversified applications. For this reason, zeolites are presently the object of a large and fast-growing interest among chemists and chemical engineers.

There are both a remote and a proximate history in the development of this book. We would like to acknowledge first the perceptiveness of the technical administrators at RCA Laboratories, Inc. during the 1970s, and in particular Dr. P. N. Yocom. Buoyed up by the financial importance of yttrium oxysulfide: europium as the red phosphor of color television tubes, they allowed us almost a decade of close cooperation aimed at understanding the performance of this phosphor. It is significant that we shared an approach to research in an industrial laboratory which allowed us to avoid the lure of "first-principles" approaches (which would have been severely premature) and freed us to formulate and to study the important issues directly. We searched for a semiquantitative understanding of the properties observed in luminescence, i. e., where energy absorption occurs, where emission occurs, and with what efficiency this conversion process takes place. We were aware that the nonradi ative transition rates found in practice vary enormously with temperature and, for a given activator, with small changes in its environment. We traced the source of this enormous variation to the magnitude of the vibrational overlap integrals, which have strong dependences on the rearrangements occurring during optical transitions and on the vibrational number of the initial electronic state. We were willing to excise from the problem the electronic aspects - the electronic wavefunctions' and their transition integrals -by treating them as parameters to be obtained from the experimental data."

Although the chemistry of boron is still relatively young, it is developing at a pace where even specific areas of research are difficult to compile into a monograph. Besides the boron hydrides, boron-nitrogen compounds are among the most fascinating derivatives of boron. Nitrogen compounds exist in a wide variety of molecular structures and display many interesting properties. The combination of nitrogen and boron, however, has some unusual features that are hard to match in any other combination of elements. This situation was first recognized by ALFRED STOCK and it seems proper to pay tribute to his outstanding work in the area of boron chemistry. One should realize that about forty years ago, STOCK and his coworkers had to develop completely new experimental techniq'\les and that no guidance for the interpreta tion of their rather unusual data had been advanced by theoretical chemists. In this monograph an attempt has been made to explore the general characteristics of structure and the principles involved in the preparation and reactions of boron-nitroge compounds. It was a somewhat difficult task to select that information which appears to be of the most interest to "inorganic and general chemistry" since the electronic relationship between a boron-nitrogen and a carbon-carbon grouping is reflected in the "organic" character of many of the reactions and compounds."

Polymer science is a technology-driven science. More often than not, technological breakthroughs opened the gates to rapid fundamental and theoretical advances, dramatically broadening the understanding of experimental observations, and expanding the science itself. Some of the breakthroughs involved the creation of new materials. Among these one may enumerate the vulcanization of natural rubber, the derivatization of cellulose, the giant advances right before and during World War II in the preparation and characterization of synthetic elastomers and semi crystalline polymers such as polyesters and polyamides, the subsequent creation of aromatic high-temperature resistant amorphous and semi-crystal line polymers, and the more recent development of liquid-crystalline polymers mostly with n~in-chain mesogenicity. other breakthroughs involve the development of powerful characterization techniques. Among the recent ones, the photon correlation spectroscopy owes its success to the advent of laser technology, small angle neutron scattering evolved from n~clear reactors technology, and modern solid-state nuclear magnetic resonance spectroscopy exists because of advances in superconductivity. The growing need for high modulus, high-temperature resistant polymers is opening at present a new technology, that of more or less rigid networks. The use of such networks is rapidly growing in applications where they are used as such or where they serve as matrices for fibers or other load bearing elements. The rigid networks are largely aromatic. Many of them are prepared from multifunctional wholly or almost-wholly aromatic kernels, while others contain large amount of stiff difunctional residus leading to the presence of many main-chain "liquid-crystalline" segments in the "infinite" network.

This volume entitled Advanced Science and Technology of Sintering, contains the edited Proceedings of the Ninth World Round Table Conference on Sintering (IX WRTCS), held in Belgrade, Yugoslavia, September 1-4 1998. The gathering was one in a series of World Round Table Conferences on Sintering organised every four years by the Serbian Academy of Sciences and Arts (SASA) and the International Institute for the Science of Sintering (IISS). The World Round Table Conferences on Sintering have been traditionally held in Yugoslavia. The first meeting was organised in Herceg Novi in 1969 and since then they have regularly gathered the scientific elite in the science of sintering. It is not by chance that, at these conferences, G. C. Kuczynski, G. V. Samsonov, R. Coble, Ya. E. Geguzin and other great names in this branch of science presented their latest results making great qualitative leaps in the its development. Belgrade hosted this conference for the first time. It was chosen as a reminder that 30 years ago it was the place where the International Team for Sintering was formed, further growing into the International Institute for the Science of Sintering. The IX WRTCS lasted four days. It included 156 participants from 17 countries who presented the results of their theoretical and experimental research in 130 papers in the form of plenary lectures, oral presentations and poster sections.

This volume had its birth from a symposium organized by the Macromolecular Secretariat of the American Chemical Society in Atlanta, GA, 1991. Since Macromolecular SeCretariat has five participating divisions-Polymer Chemistry; Polymer Materials: Science and Engineering Division; Colloid and Surface Chemistry Division; Cellulose, Paper and Textile Division; and Rubber Division-the speakers were invited from these disciplinaries and they are truly interdisciplinary in multidisciplinary areas. A number of papers are from the presentations at this symposium. However, some papers were subsequently invited to be sent in. Therefore, many papers have cited references with dates as late as this current year. This book emphasizes applications, and some of the papers were finished in 1993. Therefore, it is timely for scientists and engineers interested in this area of progress. For scientists and engineers who are not familiar with this field, since the development is still youthful, this volume will cover some new frontiers, such as electronics, medical devices, fossil fuels, asphaltics, geochemistry, and environmental engineering. With that in mind, this book can be very useful as a reference. We do include a number of review papers . in this volume. In summary, this book contains sixteen chapters with twenty-eight authors from various organizations and specialties."

The two-word title of this book can only give an indication about its content and approach to the subject it deals with. In the course of time, the term has gradually become somewhat blurred. The reason is easy to see: similar problems are now more and more frequently studied by different branches of natural science. The term "mixed crystals" has acquired specific connotations in physics, chemistry, biology, and geology. One and the same term can now serve as a name for things which are either not quite the same or sometimes quite different. And this is precisely what happened to the two words in the title of the book. One of them, the term "crystal," for which crystallography had an un ambiguous definition, is now employed by biologists to describe the structure of cell membranes and by chemists who use it to denote degrees of polymer crystallinity. "Crystal" has thus become a broad term that can help describe any solid, or just a condensed state of a substance, if the solid has a suf ficient degree of order in the arrangement of its components. But the book is called " lixed Crystals." The other word in its title, the adjective "mixed," has also developed several meanings. It is now thought ap plicable to both homogeneous and heterogeneous systems, that is, to crystals composed of different molecules and also to solids that are a mixture of crys tals with different structures."

Even brilliant colors are all bound to scatter, Who in our changing world can stay forever? From Iroha-uta, ancient Buddhistic poem of Japan For many years we have been engaged in the preparation and characterization of new metal complexes and chelates, and especially the interpretation of their electronic spectra in solutions. In the course of these studies, we have encountered a number of strange changes in color which occur upon heating, cooling or compressing the solutions, or changing the nature of the solvent. Similar effects of temperature and pressure on the color were often also observed in the solid state. Records of visual observations, spectral measurements, and their interpretations and analyses accumulated each year, until we found ourselves, quite suddenly, in the middle of a fantastic world of color changes - the world of inorganic thermochromism and related chromo tropic phenomena. This book is a result of the reviews by Sone and Prof. S. Utsuno (Kagaku no Ryoiki, 22, 222 (1968); Bunko Kenkyu, 25,123 (1976)), and a series of papers by Fukuda, Sone et al. published in the 1. Inorg. Nucl. Chern., Bull. Chern. Soc. Japan, and various other journals after 1970.

This book is devoted to nonmetal-to-metal transitions. The original ideas of Mott for such a transition in solids have been adapted to describe a broad variety of phenomena in condensed matter physics (solids, liquids, and fluids), in plasma and cluster physics, as well as in nuclear physics (nuclear matter and quark-gluon systems). The book gives a comprehensive overview of theoretical methods and experimental results of the current research on the Mott effect for this wide spectrum of topics. The fundamental problem is the transition from localized to delocalized states which describes the nonmetal-to-metal transition in these diverse systems. Based on the ideas of Mott, Hubbard, Anderson as well as Landau and Zeldovich, internationally respected scientists present the scientific challenges and highlight the enormous progress which has been achieved over the last years. The level of description is aimed to specialists in these fields as well as to young scientists who will get an overview for their own work. A common feature of all contribution is the extensive discussion of bound states," i.e. their formation and dissolution due to medium effects. This applies to atoms and molecules in plasmas, fluids, and small clusters, excitons in semiconductors, or nucleons, deuterons, and alpha-particles in nuclear matter. In this way, the transition from delocalized to localized states and vice versa can be described on a common level."

A unique selection of papers on the most recent progress in the modelling of biological molecules containing metal ions. New approaches and techniques in this field are allowing researchers to discuss structures, electronic properties and reaction mechanisms of metalloproteins on the basis of computational studies. The book discusses different approaches in the development of new force fields and their application to the computation of the structures, electronic properties and dynamics of bioinorganic compounds as well as quantum mechanical and integrated QM/MM methods for understanding the function of metalloenzymes and the calculation of electrostatic interactions.

A wonderfully successful NATO Advanced Study Institute on "Sulfur-Centered Reactive Intermediates in Chemistry and Biology" was held 18-30 June, 1989, at the Hotel Villa del Mare in Maratea, Italy. Despite the beautiful setting with mountains behind us and over looking the clear blue Mediterranean Sea under a cloudless sky (and with a private beach available), the lectures were extremely well attended. While some credit can go to the seriousness of the students, more must go to the calibre of speakers and the high quality of C. Chatgilialoglu, and Co-Director, Professor K. -D. their presentations. The Director, Dr. Asmus, are to be congratulated for putting together such an outstanding scientific program. Dr. Chatgilialoglu is also to be commended for arranging an equally stimulating social pro gram which included bus, train and boat trips to many local sites of interest. It was particularly fitting that a meeting on the chemistry and biochemistry of sulfur should be held in Italy since Italian chemists have made major contributions to our under standing of the organic chemistry of sulfur, including the chemistry of its reactive inter mediates. The early Italian interest in sulfur chemistry arose from the fact that Italy, or more specifically, Sicily, was a major world producer of sulfur prior to the development and exploitation of the Frasch process in Texas and Louisiana.

To the surprise of practically no one, research and engineering on multi polymer materials has steadily increased through the 1960s and 1970s. More and more people are remarking that we are running out of new monomers to polymerize, and that the improved polymers of the future will depend heavily on synergistic combinations of existing materials. In the era of the mid-1960s, three distinct multipolymer combinations were recognized: polymer blends, grafts, and blocks. Although inter penetrating polymer networks, lPNs, were prepared very early in polymer history, and already named by Millar in 1960, they played a relatively low-key role in polymer research developments until the late 1960s and 1970s. I would prefer to consider the IPNs as a subdivision of the graft copolymers. Yet the unique topology of the IPNs imparts properties not easily obtainable without the presence of crosslinking. One of the objectives of this book is to point out the wealth of work done on IPNs or closely related materials. Since many papers and patents actually concerned with IPNs are not so designated, this literature is significantly larger than first imagined. It may also be that many authors will meet each other for the first time on these pages and realize that they are working on a common topology. The number of applications suggested in the patent literature is large and growing. Included are impact-resistant plastics, ion exchange resins, noise-damping materials, a type of thermoplastic elastomer, and many more."

The first concern of scientists who are interested in synthetic polymers has always been, and still is: How are they synthesized? But right after this comes the question: What have I made, and for what is it good? This leads to the important topic of the structure-property relations to which this book is devoted. Polymers are very large and very complicated systems; their character ization has to begin with the chemical composition, configuration, and con formation of the individual molecule. The first chapter is devoted to this broad objective. The immediate physical consequences, discussed in the second chapter, form the basis for the physical nature of polymers: the supermolecular interactions and arrangements of the individual macromolecules. The third chapter deals with the important question: How are these chemical and physical structures experimentally determined? The existing methods for polymer characterization are enumerated and discussed in this chapter. The following chapters go into more detail. For most applications-textiles, films, molded or extruded objects of all kinds-the mechanical and the thermal behaviors of polymers are of pre ponderant importance, followed by optical and electric properties. Chapters 4 through 9 describe how such properties are rooted in and dependent on the chemical structure. More-detailed considerations are given to certain particularly important and critical properties such as the solubility and permeability of polymeric systems. Macromolecules are not always the final goal of the chemist-they may act as intermediates, reactants, or catalysts. This topic is presented in Chapters 10 and 11."

In May of 1978, several hundred of the friends, colleagues and former students of Professor Herbert C. Brown gathered on the campus of Purdue University to note his formal retirement, to honor him for his past contributions to chemistry and to wish him continued success in research. It was a time of reunion and recollection, a time for looking back and giving recognition to a lifetime of accomplishment. There was the ceremony of a banquet, presided over with inimitable wit by Professor Derek Davenport, and the dedication of the Herbert C. Brown Archives, with addresses by Dr. Alfred Bader, of Aldrich Chemicals, and Dr. Alan Schriesheim, of Exxon. There was the publi cation of a book of the personal reminiscences of students and post doctoral colleagues - "Remembering HCB." But it was also a time for looking at the present and into the future with a set of scien tific lectures, mainly by former students or associates, who des cribed their current or projected research activities. That is what this book is about. The papers, some of which are expanded versions of the lectures, fall into two broad groups - some deal with the interplay of struc ture and mechanism, the others deal with the use of organometallics in synthesis. It is, perhaps, no accident that these are the two main areas of H. C. Brown's research interest."

This book deals with selected aspects of structural chemistry, concentrating particularly on molecular and Raman spectroscopy. The authors of the various chapters were chosen from friends, colleagues and past students of Len Woodward. It is our hope that the book will prove useful both to honours students and to research workers. We would like to thank all our contributors for their willing cooperation in this endeavour. We are also grateful to all those who have given permission for the reproduction of copyright material from other publica tions; specific acknowledgments are made in each chapter. We are par ticularly indebted to the Principal and Fellows of Jesus College, Oxford, and the artist, H. A. Freeth, R.A., for permission to reproduce the portrait of Len Woodward which forms the frontispiece. Our thanks are also due to Mrs. J. Stevenson, who undertook a great deal of the secretarial work associated with the organization of this volume, and to Mr. P. Espe who photographed the portrait. The royalties from the sale of this book will, in the first instance, go to Jesus College, Oxford, and will be used for the establishment of a prize to be associated with Len Woodward's name."

The correlation of spectroscopic and chemical investigations in recent years has been highly beneficial of many reasons. Around 1950, no valid explanation was available of the colours of compounds of the five tran sition groups. Later, it was possible to identify the excited levels with those expected for an electron configuration with adefinite number of electrons in the partly filled shell. I t is not generally recognized that this is equivalent to determining spectroscopic oxidation states related to the preponderant electron configuration and not to estimates of the fractional atomic charges. This brings in an entirely different type of description than the formal oxidation numbers used for characterizing compounds and reaction schemes. However, it must be realized that collectively oxidized ligands, formation of cluster-complexes and catenation may prevent the oxidation state from being well-defined. The writer would like to express his gratitude to many, but first of all to DR. CLAUS SCHAFFER, University of Copenhagen, who is the most efficient group-theoretical engineer known to the writer; his comments and discussions have been highly valuable. The writer's colleague, Pro fessor FAUSTO CALDERAZZO (now going to the University of Pisa) has been most helpful in metallo-organic questions. Thanks are also due to Professors E. RANcKE-MADsEN and K. A. JENSEN for correspondence and conversations about formal oxidation numbers."