Micro Electro Mechanical Systems (MEMS) is already about a billion dollars a year industry and is growing rapidly. So far major emphasis has been placed on the fabrication processes for various devices. There are serious issues related to tribology, mechanics, surfacechemistry and materials science in the operationand manufacturingof many MEMS devices and these issues are preventing an even faster commercialization. Very little is understood about tribology and mechanical properties on micro- to nanoscales of the materials used in the construction of MEMS devices. The MEMS community needs to be exposed to the state-of-the-artoftribology and vice versa. Fundamental understanding of friction/stiction, wear and the role of surface contamination and environmental debris in micro devices is required. There are significantadhesion, friction and wear issues in manufacturing and actual use, facing the MEMS industry. Very little is understood about the tribology of bulk silicon and polysilicon films used in the construction ofthese microdevices. These issues are based on surface phenomenaand cannotbe scaled down linearly and these become increasingly important with the small size of the devices. Continuum theory breaks down in the analyses, e. g. in fluid flow of micro-scale devices. Mechanical properties ofpolysilicon and other films are not well characterized. Roughness optimization can help in tribological improvements. Monolayers of lubricants and other materials need to be developed for ultra-low friction and near zero wear. Hard coatings and ion implantation techniques hold promise.

For a long time, the properties of transition metal and rare earth compounds have fascinated chemists and physicists from a scientific view-point, and more recently also their enormous potential as new materials has been explored. Applications in different fields have already been realized or are under c- rent investigation, for example, new laser materials, IR to visible upconversion systems, compounds for photolithographic processes, systems involving pho- redox processes for solar energy conversion, new photovoltaic devices, chemical sensors, biosensors, electroluminescent devices (OLEDs) for flat panel display systems, supramolecular devices with wide-range definable photophysical properties, materials for energy harvesting, optical information and storage systems, etc. Metal complexes are also highly important in biology and me- cine. Most of the applications mentioned are directly related to the properties of the electronic ground state and the lower-lying excited states. Metal complexes with organic ligands or organometallic compounds exhibit outstanding features as compared to purely organic molecules. For instance, metal compounds can often be prepared and applied in different oxidation states. Furthermore, various types of low-lying electronic excitations can be induced by a suitable choice of ligands, for example, such as metal-centered transitions (MC, e. g. d-d* tran- tion), ligand-centered (LC, e. g. n-n*), metal-to-ligand-charge transfer (MLCT, e. g. d-7r*), intra-ligand-charge-transfer (ILCT) transitions, etc. In particular, the orbitals involved in the resulting lowest excited states determine the photoph- ical and photochemical properties and thus the specific use of the compoun

This treatise is a compendium of refereed papers based on invited talks presented at the American Chemical Society Symposium on Electrorheological (ER) Materials and Fluids. ER fluids were first investigated 50+ years ago. These fluids, which change rheology when placed in an electric field, were recognized, from the beginning, for allowing an extremely efficient interface between electrical control and mechanical devices. Critical problems, however, existed with the initial fluids, which prevented them from serious consideration for large-scale applications. While over time some of the critical problems have been solved and activity in ER technology has increased, commercial success has remained elusive. A recent Department of Energy report concluded that a primary reason for the failure to commercialize this promising technology is due to a lack in understanding the physics and chemistry of how the materials work. The goal of the symposium was to address the issue of understanding how ER materials work and how they can be used. One of the outcomes of the symposium, which we hope is conveyed in this book, is a feeling that if the mechanism of ER is to be fully understood and improved, expertise from diverse fields must be applied to the problem.

aiThis book starts with depiction of the phosphorus role in life creation and evolution. Then it outlines in which vital processes different phosphates participate in life of all flora and fauna, from DNA molecules till body tissues. Crucial function of phosphates was noticed long ago, but only in XIX century discovery of mineral fertilizers made it possible to sustain the needs of growing global population, thus initiating a green revolution. Though, for many decades after it, the complexity of interactions fertilizer-soil-plant roots was underrated, causing massive damages, such as soil destruction and eutrophication of waters. Still, mining of exhausting natural phosphate reserves continued worldwide. Lessons of what happened in XIX century due to scarcity of phosphates were ignored. In the meantime, production of phosphates reached its peak few years ago. Immediate implementation of phosphate recycling technologies from municipal wastes can help avoid imminent global disaster.ai

This volume contains a series of papers originally presented at the Symposium on Polymer Gels organized and sponsored by the Research Group on Polymer Gels, The Society of Polymer Science of Japan and co-sponsored by the Science and Technology Agency (ST A) and MIT , Japan. The Symposium took place at Tsukuba Science City on 18th and 19th September, 1989. Recognized experts in their fields were invited to speak and there was a strong attendance from government, academic and industrial research centers. The purpose of the Symposium was to review the state of the art and to present and discuss recent progress in the understanding of the behavioral properties of polymer gels and their application to biomedical, environmental and robotic fields. Most of the papers and related discussions concentrated on the swelling behavior of hydrogels and chemomechanical systems, both artificial and naturally occurring, in which external stimuli of a physical or chemical nature control energy transformation or signal transduction. The recent great interest in chemomechanical systems based on polymer gels has stimulated considerable effort towards the development of new sensors and actuators, controllable membrane separation processes, and delivery systems in which the functions of sensing, processing and actuation are all built into the polymeric network device. Artificial chemomechanical systems, through the use of environmentally sensitive polymer gels, are emerging as interesting materials for mimicking basic processes previously only confined to the biological world, and commercially viable applications are also foreseen in the not-too-distant future

The main objective of this book is to systematically describe the basic principles of the most widely used techniques for the analysis of physical, structural, and compositional properties of solids with a spatial resolution of approxi mately 1 ~m or less. Many books and reviews on a wide variety of microanalysis techniques have appeared in recent years, and the purpose of this book is not to replace them. Rather, the motivation for combining the descriptions of various mi croanalysis techniques in one comprehensive volume is the need for a reference source to help identify microanalysis techniques, and their capabilities, for obtaining particular information on solid-state materials. In principle, there are several possible ways to group the various micro analysis techniques. They can be distinguished by the means of excitation, or the emitted species, or whether they are surface or bulk-sensitive techniques, or on the basis of the information obtained. We have chosen to group them according to the means of excitation. Thus, the major parts of the book are: Electron Beam Techniques, Ion Beam Techniques, Photon Beam Techniques, Acoustic Wave Excitation, and Tunneling of Electrons and Scanning Probe Microscopies. We hope that this book will be useful to students (final year undergrad uates and graduates) and researchers, such as physicists, material scientists, electrical engineers, and chemists, working in a wide variety of fields in solid state sciences.

Mass spectrometry underwent dramatic changes during the decade of the 1980s. Fast atom bombardment (F AB) ionization, developed by Barber and coworkers, made it possible for all mass spectrometry laboratories to analyze polar, highly functionalized organic molecules, and in some cases ionic, inorganic, and organometallic compounds. The emphasis of much of this work was on molecular weight determination. Parallel with the development of ionization methods (molecular weight mass spectrometry) for polar biological molecules, the increased mass range of sector and quadrupole mass spectrometers and the development of new instruments for tandem mass spectrometry fostered a new era in structural mass spectrometry. It was during this same period that new instrument technologies, such as Fourier transform ion cyclotron resonance, radio frequency quadrupole ion trap, and new types of time-of-flight mass spectrometers, began to emerge as useful analytical instruments. In addi tion, laser methods useful for both sample ionization and activation became commonplace in almost every analytical mass spectrometry laboratory. In the last 5 years, there has been explosive growth in the area of biological mass spectrometry. Such ionization methods as electrospray and matrix-assisted laser desorption ionization (MALDI) have opened new frontiers for both molecular weight and structural mass spectrometry, with mass spectrometry being used for analysis at the picomole and even femto mole levels. In ideal cases, subfemtomole sample levels can be successfully analyzed. Sample-handling methods are now the limiting factor in analyz ing trace amounts of biological samples.

When we see a jumbo jet at the airport, we sometimes wonder how such a huge, heavy plane can fly high in the sky. To the extent that we think in a static way, it is certainly not understandable. In such a manner, dynamics yields behavior quite different from statics. When we want to prepare an iron nitride, for example, one of the most orthodox ways is to put iron in a nitrogen atmosphere under pressures higher than the dissociation pressure of the iron nitride at temperatures sufficiently high to let the nitrogen penetrate into the bulk iron. This is the way thermodynamics tells us to proceed, which requires an elaborate, expensive high-pressure apparatus, sophisticated techniques, and great efforts. However, if we flow ammonia over the iron, even under low pressures, we can easily prepare the nitride-provided the hydrogen pressure is sufficiently low. Since the nitrogen desorption rate is the determining step of the ammonia decomposition on the iron surface, the virtual pressure of nitrogen at the surface can reach an extremely high level (as is generally accepted) because, in such a dynamic system, the driving force of the ammonia decomposition reaction pushes the nitrogen into the bulk iron to form the nitride. Thus, dynamics is an approach considerably different from statics.

Mechanisms of Inorganic and Organometallic Reactions provides an ongoing critical review of the primary literature concerned with mechanisms of inorganic and organometallic reactions. The main focus is on reactions in solution, although solid-state and gas-phase studies are included where they provide relevant mechanistic insight. Each volume covers an eighteen-month literature period, and this, the eighth volume in the series, includes papers published during January 1990 through June 1991. Where appropriate, references to earlier reports and to specific sections in previous volumes are given. Coverage spans the whole area as comprehensively as possible in each volume, and while it is impossible to be absolutely exhaustive, every effort is made to include all of the important published work that is relevant to the elucidation of reaction mechanisms. Numerical data are reported in the units used by the original authors, and they are converted to common units only when comparisons are being made. The successful format of earlier volumes is retained to facilitate tracing progress over several years in a particular topic, and the series now permits this to be done for a twelve-year period. The introduction three volumes ago of computerized techniques to improve cross-referencing in the Index brought positive reader comments, and their use is being continued.

Boron has all the best tunes. That may well be the first impression of the Group 13 elements. The chemical literature fosters the impression not only in the primary journals, but also in asteady outflowofbooks focussing more or less closely on boron and its compounds. The same preoccupation with boron is apparent in the coverage received by the Group 13 elements in the comprehensive and regularly updated volume of the Gmelin Handbook. Yet such an imbalance cannot be explained by any inherent lack ofvariety, interest or consequence in the 'heavier elements. Aluminium is the most abundant metal in the earth's crust; in the industrialised world the metal is second only to iron in its usage, and its compounds can justifiably be said to touch our lives daily - to the potential detriment of those and other lives, some would argue. From being chemical curios, gallium and indium have now gained considerably prominence as sources of compound semiconductors like gallium arsenide and indium antimonide. Nor is there any want ofincident in the chemistriesofthe heavier Group 13 elements. In their redox, coordination and structural properties, there is to be found music indeed, notable not always for its harmony but invariably for its richness and variety. Thisbook seeks to redress the balance with a definitive, wide-rangingand up-to-date review of the chemistry of the Group 13 metals aluminium, gallium, indium and thallium.

This series of books, which is published at the rate of about one per year, addresses fundamental problems in materials science. The contents cover a broad range of topics from small clusters of atoms to engineering materials and involve chemistry, physics, and engineering, with length scales ranging from Angstromsup to millimeters. The emphasis is on basic science rather than on applications. Each book focuses on a single area ofcurrent interest and brings together leading experts to give an up-to-date discussion of their work and the work ofothers. Each article contains enough references that the interested reader can accesstherelevant literature. Thanks aregiven to the Center forFundamental Materials Research atMichigan State University forsupportingthis series. M.F. Thorpe, Series Editor E-mail: [email protected] EastLansing, Michigan, September, 1995 PREFACE This book records selected papers given at an interdisciplinary Symposium on Access in Nanoporous Materials held in Lansing, Michigan, on June 7-9, 1995. Broad interest in the synthesis of ordered materials with pore sizes in the 1.0-10 nm range was clearly manifested in the 64 invited and contributed papers presented by workers in the formal fields of chemistry, physics, and engineering. The intent of the symposium was to bring together a small number ofleading researchers within complementary disciplines to share in the diversity of approaches to nanoporous materials synthesis and characterization."

Environmental pollution is one of the main problems to confront humanity, with the heavy metals occupying a leading role among the most pernicious pollutants. The metals cause cancer and other sicknesses. Their cytotoxic, mutagenic and carcinogenic potentials are not fully understood, and any thorough investigation demands the combined efforts of scientists drawn from many different disciplines. But the effects of heavy metals are not all negative: some, like cis-DDP, and some ruthenium and tin complexes, have antitumour activity. The idea underlying the present work is therefore to present a multidisciplinary perspective on heavy metals in the environment, affording a better understanding of their action on human organisms and health, aiming to make them less polluting and more environmentally friendly.

The intrinsic properties of a solid, i. e. , the properties that result from its specific structure, can be largely modified by crystallographic and chem ical defects. The formation of these defects is governed by the heat and mass transfer conditions which prevail on and near a crystal-nutrient in terface during crystallization. Hence, both the growth of highly perfect crystals and the preparation of samples having predetermined defect-induced (extrinsic) properties require a thorough understanding of the reaction and transport mechanisms that govern crystallization from vapors, solutions and melts. Crystal growth, as a science, is therefore mostly concerned with the chemistry and physics of heat and mass transport in these fluid-solid phase transitions. Solid-solid transitions are, at this time, not widely employed for high quality single-crystal production. Transport concepts are largely built upon equilibrium considerations, i. e. , on thermodynamic and phase equilibrium concepts. Hence to supply a "workable" foundation for the succeeding discussions, this text begins in Chapter 2 with a concise treatment of thermodynamics which emphasizes applications to mate rials preparation. After working through this chapter, the reader should feel at ease with often (particularly among physicists) unfamiliar entities such as chemical potentials, fugacities, activities. etc. Special sections on ther mochemical calculations (and their pitfalls) and compilations of thermochemi cal data conclude the second chapter. Crystal growth can be called. in a wide sense, the science and technology of controlling phase transitions that lead to (single crystalline) solids.

Radiationless transitions comprise an important class of physical phenomena occurring in the excited states of molecules. They affect the lifetimes of the ex cited states and govern primary photochemical and photophysical processes. Much effort has been devoted to the understanding of radiationless transi tions. Still, owing to recent advances, the field continues to attract attention. The demand for a book on the theory of these processes naturally arises in at tempting to comprehend a large body of literature, as the famous review article by K. F. Freed and the book by R. Englman do not encompass some issues of current interest. Our intent is to highlight the underlying physical principles and methods in such a way that the book both in its content and its presentation is instruc tive for a wide audience. The basic ideas are treated in simple mathematical terms intelligible to ex perimentalists and to readers unfamiliar with the field. Complicated theoret ical methods are always expounded from first principles, so that a knowledge of quantum mechanics and mathematics at the graduate-student level will enable the reader to easily follow the derivations. Experts will find efficient methods of calculating the transition rates, as well as new applications of quasiclassical methods and fresh treatments of standard problems. Details of measurements are not discussed, and experimental data are only invoked to illustrate the theory."

An overview of modern organometallic thermochemistry, made by some of the most active scientists in the area, is offered in this book. The contents correspond to the seventeen lectures delivered at the NATO ASI Energetics of Organometallic Species (Curia, Portugal, September 1991), plus three other invited contributions from participants of that summer school. These papers reflect a variety of research interests, and discuss results obtained with several techniques. It is therefore considered appropriate to add a few preliminary words, attempting to bring some unity out of that diversity. In the first three chapters, results obtained by classical calorimetric methods are described. Modern organometallic thermochemistry started in Manchester, with Henry Skinner, and his pioneering work is briefly surveyed in the first chapter. The historical perspective is followed by a discussion of a very actual issue: the trends of stepwise bond dissociation enthalpies. Geoff Pilcher, another Manchester thermochemist, makes, in chapter 2, a comprehensive and authoritative survey of problems found in the most classical of thermochemical techniques - combustion calorimetr- applied to organometallic compounds. Finally, results from another classical technique, reaction-solution calorimetry, are reviewed in the third chapter, by Tobin Marks and coworkers. More than anybody else, Tobin Marks has used thermochemical values to define synthetic strategies for organometallic compounds, thus indicating an application of thermochemical data of which too little use has been made so far.

Mixed valency is one of various names used to describe compounds which contain ions of the same element in two different formal states of oxidation. The existence of mixed valency systems goes far back into the geological evolutionary history of the earth and other planets, while a plethora of mixed valency minerals has attracted attention since antiquity. Indeed, control of the oxidation states of Fe in its oxides (FeO, Fe304' Fe203) was elegantly used in vase painting by the ancient Greeks to produce the characteristic black and red Attic ceramics (Z. Goffer, "Archaeological Chemistry," Wiley, New York, 1980). It was, however, only 25 years ago that two reviews of mixed valency appeared in the literature almost simultaneously, signalling the first attempt to treat mixed valency systems as a separate class of compounds whose properties can be correlated with the molecular and the electronic structure of their members. Then mixed valency phenomena attracted the interest of disparate classes of scientists, ranging from synthetic chemists to solid state physicists and from biologists to geologists. This activity culminated with the NATO ASI meeting in Oxford in 1979. The 1980's saw again a continuing upsurge of interest in mixed valency. Its presence is a necessary factor in the search for highly conducting materials, including molecular metals and superconductors. The highly celebrated high T c ceramic superconducting oxides are indeed mixed valency compounds.

Modular Chemistry: the First Steps In recent years, there has been increasing interest among chemists, physicists, materials scientists, biologists, engineers, and others in the assembly of well defmed, relatively large functional structures from repetitive units that themselves are molecules of some complexity. Using the dictionary defmition of a module (a detachable section, compartment, or unit with a specific purpose or function, and in electronics, a compact assembly functioning as a component of a larger unit) [1], we feel that this newly emerging field of endeavor could be called "modular chemistry" [2]. The NATO Advanced Research Workshop on Modular Chemistry that was held on September 9 to 12, 1995, at Aspen Lodge near Estes Park, Colorado, was meant to bring together prominent contributors to modular chemistry as it is being born, and to examine the associated birth pangs. It was concluded that although real, these are not nearly as bad as giving birth to a hedgehog tail first, and that the ultimate rewards were likely to be far more satisfying in terms of new ideas and enabling methodology. The level of excitement about the possibilities that are opening up for modular chemists, and also the challenge involved, are perhaps best documented by noting that the planned discussion periods at the workshop were as long as the oral presentation periods, and yet, each discussion ran over the allocated time.

Crystal pulling is an industrial process and provides the bulk of semiconductor crystals for the semiconductor industry. Initially a purely empirical process, the increase in importance and size of the industry has led to basic research into the fundamentals of the process - particularly the modelling of heat and mass transfer. The book has been written by the recognized authority on Czochralski crystal-growth techniques. It is an attempt to strengthen the interface between the practical crystal grower and the applied mathematician involved in analytical and computer modelling. Its focus is on the physics, chemistry and metallurgy of the process. From reviews: "... There is a need for a modern, non-trivial text on Czochralski growth ... and Dr. Hurle is eminently suited to write such a text."; "Dr. Hurle is probably uniquely qualified to write a book on ... (the Czochralski) growth process. ... He has published a great deal of very substantial as well as innovative work in this area."

To the biochemist, water is, of course, the only solvent worthy of consideration, because natural macromolecules exhibit their remarkable conformational properties only in aqueous media. Probably because of these remarkable properties, biochemists do not tend to regard proteins, nucleotides and polysaccharides as polymers in the way that real polymer scientists regard methyl methacrylate and polyethylene. The laws of polymer statistics hardly apply to native biopolymers. Between these two powerful camps, lies the No-man's land of water soluble synthetic polymers: here, we must also include natural polymers which have been chemically modified. The scientific literature of these compounds is characterized by a large number of patents, which is usually a sign of little basic understanding, of 'know-how' rather than of 'know-why'. Many of the physical properties of such aqueous solutions are intriguing: the polymer may be completely miscible with water, and yet water is a 'poor' solvent, in terms of polymer parlance. ~kiny of the polymers form thermorever sible gels on heating or cooling. The phenomena of exothermic mixing and salting-in are common features of such systems: neither can be fully explained by the available theories. Finally, the eccentric behaviour of polyelectrolytes is well documented. Despite the lack of a sound physico-chemical foundation there is a general awareness of the importance of water soluble vinyl, acrylic, polyether, starch and cellulose derivatives, as witnessed again by ~he vast patent literature.

Hydroxyapatite is the structural prototype of the main inorganic constituent of bone and teeth and, together with fluorapatite, is also one of the principal minerals in commercial phosphate ores. The adsorption characteristics and surface chemistry of hydroxyapatite are important in understanding the growth, dissolution and adhesion mechanisms of bone and tooth tissues and in elucidating the factors in mineral beneficiation such as floation and flocculation. This volume essentially documents the proceedings of the symposium on the same topic held at the American Chemical Society Meeting in Kansas City, MO, September 12-17, 1982. It includes a few papers which were not presented at the symposium but does not comprise the entire program. This volume provides, on a limited scale, a multidisciplinary overview of current work in the field of adsorptive behavior and surface chemistry of hydroxyapatite and includes certain review articles. There are two papers each on adsorption, adsorption and its effects on crystal growth or dissolution kinetics, effects of electrochemical parameters on solubility and adsorption, and newer physical methods (exoemission and high-resolution NMR) of examining hydroxyapatite surface. There is one paper each on structure modelling of apatite surface based on octacalcium phosphate interface and on biodegradation of sintered hydroxyapatite.

The discovery of the antitumour activity of cisplatin in 1965 and its subsequent introduction into clinical trials in 1971 was the catalyst for a major international research effort investigating the potential of metal compounds in cancer therapy. Cisplatin now occupies an important place in the armamentarium of the oncologist due to its effectiveness in the treatment of testicular cancer. A second generation analogue, carbo platin, offers reduced toxicity together with therapeutic activity, which gives it a place in the front-line therapy of genitourinary cancers. These and other successes have encouraged the search for novel metal-based drugs for cancer therapy. Research has shown that metal compounds have potential for activity not only as cytotoxic antitumour agents, but also in areas such as adjuvant therapy, diagnosis and immunotherapy. The aim of this book is to review and describe the major achievements and developments arising from this international research effort. The contributing authors come from labora tories throughout Europe and America and represent the many disci plines characteristic of this research, such as clinical research, pharmacology, tumour biology and inorganic medicinal chemistry."

This book is intended to collect in one place as much information as possible on the use of EPR spectroscopy in the analysis of systems in which two or more spins are magnetically coupled. This is a field where research is very active and chemists are elbow-to-elbow with physicists and biologists in the forefront. Here, as in many other fields, the contributions coming from different disciplines are very important, but for active researchers it is sometimes difficult to follow the literature, due to differences in languages, and sources which are familiar to, e. g. , a physicist, are exotic to a chemist. Therefore, an effort is needed in order to provide a unitary description of the many different phenomena which are collected under the title. In order to define the arguments which are treated, it is useful to state clearly what is not contained here. So we do not treat magnetic phenomena in conductors and we neglect ferro- and antiferromagnetic resonance. The basic foundations of EPR spectroscopy are supposed to be known by the reader, while we introduce the basis of magnetic interactions between spins. In the first two chapters we review the foundations of exchange interactions, trying to show how the magnetic parameters are bound to the electronic structure of the interacting centers.

The International Winter School on Electronic Properties of High-Temperature Superconductors, held between March 7-14, 1992, in Kirchberg, (Tyrol) Austria, was the sixth in a series of meetings to be held at this venue. Four of the earlier meetings were dedicated to issues in the field of conducting polymers, while the winter school held in 1990 was devoted to the new discipline of high-T c superconductivity. This year's meeting constituted a forum not only for the large number of scientists engaged in high-Tc research, but also for those involved in the new and exciting field of fullerenes. Many of the issues raised during the earlier winter schools on conducting polymers, and the last one on high-T c superconductivity, have taken on a new significance in the light of the discovery of superconducting C materials. 60 The Kirchberg meetings are organized in the style of a school where expe rienced scientists from universities, research laboratories and industry have the opportunity to discuss their most recent results, and where students and young scientists can learn about the present status of research and applications from some of the most eminent workers in their field. In common with the previous winter school on high-Tc superconductors, the of the cuprate superconductors. present one focused on the electronic properties In addition, consideration was given to related compounds which are relevant to the understanding of the electronic structure of the cuprates in the normal state, to other oxide superconductors and to fulleride superconductors.

Carbosilanes are compounds in which the elements silicon and carbon alternate in the molecular skeleton [1]. Just as the alkanes are formally derived from the diamond lattice and the aromatics from the graphite lattice, the carbosilanes are structurally derived from silicon carbide. Because of the tetravalent nature of silicon and carbon we can expect stable linear, cyclic and polycyclic compounds to occur. However, carbosilanes do not exist in nature. This book is an attempt to give a summarized presentation. Carbosilanes are, of course, part" of organosilicon chemistry, but their behavior differentiates them distinctly from other organosilicon compounds. The differences result primarily from the alternating Si-C-Si arrangements in the molecular skeleton, and especially the various methylene bridges (CH , CHX, CX ; X = halogen) cause changes in z z Si-C bond polarization and hence influence the reaction possibilities. It is convenient to regard carbosilanes as similar to silicones except that the oxygen bridges of silicones are replaced by methylene units. However, this does not accurately account for all the chemical properties of these compounds. Carbosilanes are related more directly to silicon carbide, as shown occasionally by the reactive behavior of polycyclic car bosilanes. Therefore, in view of the present interest shown for thermally stable cera mics of unusual character, interesting possibilities arise for further development. Most cyclic carbosilanes can be classified in two groups: the carborundanes and the Si-scaphanes. Compounds belonging to the carborundane class maintain Si-C six-membered rings in the boat conformation.

The field of transition metal catalysis has experienced incredible growth during the past decade. The reasons for this are obvious when one considers the world's energy problems and the need for new and less energy demanding syntheses of important chemicals. Heterogeneous catalysis has played a major industrial role; however, such reactions are generally not selective and are exceedingly difficult to study. Homogeneous catalysis suffers from on-site engineering difficulties; however, such reactions usually provide the desired selectivity. For example, Monsanto's synthesis of optically-active amino acids employs a chiral homogeneous rhodium diphosphine catalyst. Industrial uses of homogeneous catalyst systems are increasing. It is not by accident that many homogeneous catalysts contain tertiary phosphine ligands. These ligands possess the correct steric and electronic properties that are necessary for catalytic reactivity and selectivity. This point will be emphasized throughout the book. Thus the stage is set for a comprehensive be treatment of the many ways in which phosphine catalyst systems can designed, synthesized, and studied."