Modern Inorganic Chemistry – serie

Molecular clusters, in the broad sense that the term is commonly understood, today comprise an enormous class of species extending into virtually every important area of chemistry: "naked" metal clusters, transition metal carbonyl clusters, hydrocarbon cages such as cubane (C H ) and dodecahedrane (C H ), 8 8 20 20 organometallic cluster complexes, enzymes containing Fe S or MoFe S 4 4 3 4 cores, high polymers based on carborane units, and, of course, the many kinds of polyhedral borane species. So large is the area spanned by these diverse classes that any attempt to deal with them comprehensively in one volume would, to say the least, be ambitious-and also premature. We are presently at a stage where intriguing relationships between the various cluster families are becoming apparent (particularly in terms of bonding descriptions), and despite large dif­ ferences in their chemistry an underlying unity is gradually developing in the field. For example, structural changes occurring in Fe S cores as electrons are 4 4 pumped in and out, in some measure resemble those observed in boranes and carboranes. The cleavage of alkynes via incorporation into carborane cages and subsequent cage rearrangement, a sequence familiar to boron chemists, is a thermodynamically favored process which may be related to the behavior of unsaturated hydrocarbons on metal surfaces; analogies of this sort have drawn attention from theorists and experimentalists.

When presented with a new compound or material, the inorganic chemist will usually have several questions in mind about its composition and structure. Although a simple elemental analysis may answer many questions about its composition, the chemist will still have questions about its structure, and, ifthe material contains a metal atom, he will often want to know its oxidation state, coordination number and geometry. Further, at an increasingly frequent rate, the chemist may need details of the spin­ state, magnetic and perhaps dynamic properties of the material. If the investigator is fortunate, the material or compound may contain an ele­ ment such as iron, tin, antimony, iodine, gold, or one of several of the rare earth metals which are amenable to study by the Mossbauer effect. Often the Mossbauer effect can, sometimes with quite simple experiments, provide the answers to all of these questions. The goal of this book is to illustrate the effectiveness of the Mossbauer effect in providing the answers to the many questions that arise in char­ acterizing new materials and, indeed, in studying known materials in more detail. Several chapters introduce the effect to the novice and provide details about the various hyperfine interactions that are the "bread and butter" of the Mossbauer spectroscopist. Three chapters deal specifically with the experimental aspects of the technique and the increasing impor­ tance of sophisticated computer analysis of the resulting data.

In 1988 the Mossbauer effect community completed 30 years of continual contribution to the fields of nuclear physics, solid state science, and a variety of related disciplines. To celebrate this anniversary, Professor Gonser of the Universitat des Saarlandes has contributed a chapter to this volume on the history of the effect. Although Mossbauer spectroscopy has reached its mature years, the chapters in this volume illustrate that it is still a dynamic field of science with applications to topics ranging from permanent magnets to biologi­ cal mineralization. During the discussion of a possible chapter for this volume, a potential author asked, "Do we really need another Mossbauer book?" The editors responded in the affirmative because they believe that a volume of this type offers several advantages. First, it provides the author with an opportunity to write a personal view of the subject, either with or without extensive pedagogic content. Second, there is no artificially imposed restriction on length. In response to the question, "How long should my chapter be?," we have responded that it should be as long as is necessary to clearly present, explain, and evaluate the topic. In this type of book, it is not necessary to condense the topic into two, four, or eight pages as is now so often a requirement for publication in the research literature.

Organometallic chemistry belongs to the most rapidly developing area of chemistry today. This is due to the fact that research dealing with the structure of compounds and chemical bonding has been greatly intensified in recent years. Additionally, organometallic compounds have been widely utilized in catalysis, organic synthesis, electronics, etc. This book is based on my lectures concerning basic organometallic chemistry for fourth and fifth year chemistry students and on my lectures concerning advanced organometallic chemistry and homogeneous catalysis for Ph.D. graduate students. Many recent developments in the area of organometallic chemistry as weIl as homogeneous catalysis are presented. Essential research results dealing with a given class of organometallic compounds are discussed briefly. Results of physicochemical research methods of various organometallic compounds as weIl as their synthesis, properties, structures, reactivities, and applications are discussed more thoroughly. The selection of tabulated data is arbitrary because, often, it has been impossible to avoid omissions. Nevertheless, these data can be very helpful in understanding properties of organometaIlic compounds and their reactivities. All physical data are given in SI units; the interatomic distances are given in pm units in figures and tables. I am indebted to Professor S. A. Duraj for translating and editing this book. His remarks, discussions, and suggestions are greatly appreciated. I also express gratitude to Virginia E. Duraj for editing and proofreading.

There is a certain fascination associated with words. The manipulation of strings of symbols according to mutually accepted rules allows a language to express history as well as to formulate challenges for the future. But language changes as old words are used in a new context and new words are created to describe changing situations. How many words has the computer revolution alone added to languages? "Inorganometallic" is a word you probably have never encountered before. It is one created from old words to express a new presence. A strange sounding word, it is also a term fraught with internal contradiction caused by the accepted meanings of its constituent parts. "In­ organic" is the name of a discipline of chemistry while "metallic" refers to a set of elements constituting a subsection of that discipline. Why then this Carrollian approach to entitling a set of serious academic papers? Organic, the acknowledged doyenne of chemistry, is distinguished from her brother, inorganic, by the prefix "in," i. e. , he gets everything not organic. Organometallic refers to compounds with carbon-metal bonds. It is simple! Inorganometallic is everything else, i. e. , compounds with noncarbon-metal element bonds. But why a new term? Is not inorganic sufficient? By virtue of training, limited time, resources, co-workers, and so on, chemists tend to work on a specific element class, on a particular compound type, or in a particular phase. Thus, one finds element-oriented chemists (e. g.

During the past 30 years materials science has developed into a full-fledged field for basic and applied scientific enquiry. Indeed, materials scientists have devoted their efforts to creating new materials with improved electronic, magnetic, thermal, mechanical, and optical properties. Often unnoticed, these new materials are rapidly invading our homes and automobiles, and may be found in our utensils, electronic equipment, textiles, home appliances, and electric motors. Even though they may go unnoticed, these new materials have either improved the efficiency and lifetime of these items or have reduced their weight or cost. In particular, magnetically ordered materials are useful in various applications, such as motors, magnetic imaging, magnetic recording, and magnetic levitation. Hence, much effort has been devoted to the development of better hard magnetic materials, magnetic thin films, and molecular magnets. During the same period of time, Mossbauer-effect spectroscopy has grown from a laboratory curiosity to a mature spectroscopic technique, a technique that probes solid-state materials at specific atomic sites and yields microscopic information on the magnetic and electronic properties of these materials. Iron-57 is the most commonly and easily used Mossbauer-effect isotope and, of course, is particularly relevant for the study of magnetic materials. Various applications of Mossbauer spectroscopy to magnetic materials are discussed in the first six chapters of this volume. Other isotopes such as zinc-67 and gadolinium-ISS have recently been used to study the electronic properties of zinc compounds and the electronic and magnetic properties of rare-earth transition metal compounds.

Focusing on practical applications, the author provides a balanced introduction to the many possible technological uses of metal complexes. Coverage includes the transition metals, lanthanide and actinide complexes, metal porphyrins, and many other complexes. This volume meets the needs of students and scientists in inorganic chemistry, chemical physics, and solid-state physics.

This book by Kaplan and Vekhter brings together the molecular world of the chemist with the condensed matter world of the physicist. Prior to the collapse of the Soviet Union, chemists in the West devoted lit­ to relationships between molecular electronic structure and tle attention solid-state vibronic phenomena. Treating quantum mechanical problems wherein the adiabatic Born-Oppenheimer approximation fails was done by "brute force. " With bigger and better computers available in the West, molecular orbital calculations were done on observed and conceived static structures with little concern for any cooperativity of vibrational behavior that might connect these states. While it had long been understood in the West that situations do occur in which different static structures are found for molecules that have identical or nearly identical electronic structures, little attention had been paid to understanding the vibrational states that could connect such structures. It was easier to calculate the electronic structure observed with several possible distortions than to focus on ways to couple electronic and vibrational behavior. In the former Soviet Union, computational power was not as acces­ sible as in the West. Much greater attention, therefore, was devoted to conserving computational time by considering fundamental ways to han­ dle the vibrational connectivity between degenerate or nearly degenerate electronic states.

Stability constants are fundamental to understanding the behavior of metal ions in aqueous solution. Such understanding is important in a wide variety of areas, such as metal ions in biology, biomedical applications, metal ions in the environment, extraction metallurgy, food chemistry, and metal ions in many industrial processes. In spite of this importance, it appears that many inorganic chemists have lost an appreciation for the importance of stability constants, and the thermodynamic aspects of complex formation, with attention focused over the last thirty years on newer areas, such as organometallic chemistry. This book is an attempt to show the richness of chemistry that can be revealed by stability constants, when measured as part of an overall strategy aimed at understanding the complexing properties of a particular ligand or metal ion. Thus, for example, there are numerous crystal structures of the Li+ ion with crown ethers. What do these indicate to us about the chemistry of Li+ with crown ethers? In fact, most of these crystal structures are in a sense misleading, in that the Li+ ion forms no complexes, or at best very weak complexes, with familiar crown ethers such as l2-crown-4, in any known solvent. Thus, without the stability constants, our understanding of the chemistry of a metal ion with any particular ligand must be regarded as incomplete. In this book we attempt to show how stability constants can reveal factors in ligand design which could not readily be deduced from any other physical technique.

This book represents Volume 2 in a series on the use of Mossbauer spectroscopy in the study of magnetism and materials. However, the perceptive reader will notice some differences from Volume 1. Specifically, in order to market the book at a more affordable price for most universities and research laboratories, the book has been prepared in camera­ ready format The editors and the authors agreed to do this because there is a demand for such a book in the Mossbauer community. This format has placed an extra burden on the editors and the authors and we hope we have overcome all the difficulties generated by the transfer of files between different computers. In order to make the book more attractive to materials scientists who are not experts in Mossbauer spectroscopy, this volume is particularly oriented towards the study of materials by Mossbauer spectroscopy and related complementary techniques, such as neutron scattering and a variety of surface scattering techniques. The authors of this volume can be proud of the high quality professional effort they have devoted to clearly presenting their specific topics. As a result we very much enjoyed working with the authors on this volume. We hope that their effort will help to educate the next generation of Mossbauer effect spectroscopists, a generation which will face the challenge of maintaining equally high scientific and professional standards in their research work.

This book is intended to offer the reader a snapshot of the field of optoelectronic materials from the viewpoint of inorganic chemists. The field of inorganic chemistry is transforming from one focused on the synthesis of compounds having interesting coordination numbers, structures, and stereochemistries, to one focused on preparing compounds that have potentially useful practical applica­ tions. Two such applications are in the area of optics and electronics. These are fields where the use of inorganic materials has a long history. As the field of microelectronics develops the demands on the performance of such materials increases, and it becomes necessary to discover compounds that will meet these demands. The field of optoelectronics represents a merging of the two disciplines. Its emergence is a natural one because many of the applications involve both of these properties, and also because the electronic structure of a metal compound that confers novel optical properties is often one that also influences its electron transfer and conductivity characteristics. Two of the more important growth areas that have led to these developments are communications and medicine. Within the communications field there is the microelectronics that is involved in information storage and transmittal, some of which will be transferred into the optical regime. Within the medical field there are chemical probes that transmit analytical information from an in vivo environment. This information needs to be readily accessible from an external site, and then quickly converted into images or data that yield accurate and inexpensive diagnoses.

According to R.H. Crabtree, Metal Dihydrogen and sigma-Bond Complexes is described as `the definitive account of twentieth-century work in the area of sigma complexation'. It covers not only Kubas' discovery of dihydrogen coordination and the study of its structure and general properties but also discusses both the theoretical beliefs and experimental results of bonding and activation of dihydrogen on metal centers and the coordination and activation of C-H, B-H, X-H, and X-Y bonds, giving an overview of `one of the hottest areas in chemistry'.

Extractions of Metals from Soils and Waters represents a new emphasis in the series Modern Inorganic Chemistry, namely the impact inorganic chemistry can have on the environment. Also, this is the first volume ever to introduce the reader to all aspects of heavy metal extraction. While the primary emphasis is on complexation chemistry, attention is also paid to phase transfer aspects. Particular methods of note include electrokinetics, phytoremediation, and sensors. Aimed primarily at chemists, this book will also appeal to engineers, plant biochemists, environmental health specialists, and practitioners or students of environmental law.

The book examines the suitability of nanoscale zero-valent iron (ZVI) for degradation of agrochemicals for the purpose of developing a cost-effective treatment technology. It identifies by-products produced from the ZVI-mediated degradation process of particular contaminants, and clarifies the reaction mechanism by which ZVI degrades a chosen contaminant.It also assesses how the ZVI-based technology may be applied in complex, natural systems, the limitations to implementation, and possible avenues for further research which might improve the viability of the process.

The book examines the suitability of nanoscale zero-valent iron (ZVI) for degradation of agrochemicals for the purpose of developing a cost-effective treatment technology. It identifies by-products produced from the ZVI-mediated degradation process of particular contaminants, and clarifies the reaction mechanism by which ZVI degrades a chosen contaminant.It also assesses how the ZVI-based technology may be applied in complex, natural systems, the limitations to implementation, and possible avenues for further research which might improve the viability of the process.

This book is intended to offer the reader a snapshot of the field of optoelectronic materials from the viewpoint of inorganic chemists. The field of inorganic chemistry is transforming from one focused on the synthesis of compounds having interesting coordination numbers, structures, and stereochemistries, to one focused on preparing compounds that have potentially useful practical applica­ tions. Two such applications are in the area of optics and electronics. These are fields where the use of inorganic materials has a long history. As the field of microelectronics develops the demands on the performance of such materials increases, and it becomes necessary to discover compounds that will meet these demands. The field of optoelectronics represents a merging of the two disciplines. Its emergence is a natural one because many of the applications involve both of these properties, and also because the electronic structure of a metal compound that confers novel optical properties is often one that also influences its electron transfer and conductivity characteristics. Two of the more important growth areas that have led to these developments are communications and medicine. Within the communications field there is the microelectronics that is involved in information storage and transmittal, some of which will be transferred into the optical regime. Within the medical field there are chemical probes that transmit analytical information from an in vivo environment. This information needs to be readily accessible from an external site, and then quickly converted into images or data that yield accurate and inexpensive diagnoses.

Extractions of Metals from Soils and Waters represents a new emphasis in the series Modern Inorganic Chemistry, namely the impact inorganic chemistry can have on the environment. Also, this is the first volume ever to introduce the reader to all aspects of heavy metal extraction. While the primary emphasis is on complexation chemistry, attention is also paid to phase transfer aspects. Particular methods of note include electrokinetics, phytoremediation, and sensors. Aimed primarily at chemists, this book will also appeal to engineers, plant biochemists, environmental health specialists, and practitioners or students of environmental law.

This book by Kaplan and Vekhter brings together the molecular world of the chemist with the condensed matter world of the physicist. Prior to the collapse of the Soviet Union, chemists in the West devoted lit­ to relationships between molecular electronic structure and tle attention solid-state vibronic phenomena. Treating quantum mechanical problems wherein the adiabatic Born-Oppenheimer approximation fails was done by "brute force. " With bigger and better computers available in the West, molecular orbital calculations were done on observed and conceived static structures with little concern for any cooperativity of vibrational behavior that might connect these states. While it had long been understood in the West that situations do occur in which different static structures are found for molecules that have identical or nearly identical electronic structures, little attention had been paid to understanding the vibrational states that could connect such structures. It was easier to calculate the electronic structure observed with several possible distortions than to focus on ways to couple electronic and vibrational behavior. In the former Soviet Union, computational power was not as acces­ sible as in the West. Much greater attention, therefore, was devoted to conserving computational time by considering fundamental ways to han­ dle the vibrational connectivity between degenerate or nearly degenerate electronic states.

This volume is concerned with methods that are available for the calculation of for­ mation constants, in particular computational procedures. Although graphical meth­ ods have considerable value in the exploration of primary (raw) data they have been overtaken by computational methods, which, for the most part, take primary data and return the refined formation constants. Graphical methods are now considered com­ plementary to these general computational procedures. This volume brings together programs that span the lifetime of computer-assisted determination of formation constants. On one hand the reader will find listings of programs that are derived from LETAGROP (b.l961) and the GAUSS-G/SCOGS (b. 1962) families. On the other hand programs are presented that are the newest mem­ bers of the SCOGS lineage and from the on-going MINIQUAD series. One program is presented that describes a computational approach to the classical Hedstrom­ Osterberg methods; another that takes care of electrode calibration in a simple yet rigorous manner. Potentiometry and spectrophotometry are the most popular experimental tech­ niques for equilibrium studies, and the programs in this volume reflect this. Four programs handle potentiometric data, two will process spectrophotometric data, and one makes use of both types of data separately or in combination.

The field of gas phase inorganic ion chemistry is relatively new; the early studies date back approximately twenty years, but there has been intense interest and development in the field in the last ten years. As with much of modern chemistry, the growth in gas phase inorganic ion chemistry can be traced to the development of instrumentation and new experimental methods. Studies in this area require sophisticated instruments and sample introduc­ tion/ ionization methods, and often these processes are complicated by the need for state-selecting (or collisionally stabilizing) the reactive species in order to assign the chemistry unequivocally. At the present level of experimental development, a wide range of experiments on diverse ionic systems are possible and many detailed aspects of the chemistry can be studied. Gas Phase Inorganic Chemistry focuses on the reactions of metal ions and metal clusters, and on the study of these species using the available modern spectroscopic methods. Three of the twelve chapters cover the chemistry of ionic monometal transition metal ions and the chemistry of these species with small diatomics and model organics. Two of the chapters focus on the studies of the chemical and physical properties of (primarily) transition metal clusters, and these chapters review experimental methods and capabilities. Two chapters also deal with the chemistry of transition metal carbonyl clusters, and these chapters address issues important to cluster growth and activation as well as the characterization of such species.

The term "carbon-functional organosilicon compound" is used for organosilicon compounds in which a functional group is bonded to an organic moiety that is in turn con­ nected to silicon via a Si-C bond. Thus, only Si-Cn-Y com­ pounds (Y designates a functional group) will be discussed in this book 1 Si-O-Cn-Y compounds will in general not be considered, although the latter group does include a large number of natural substances containing silylated hydroxyl groups. (Because of the differing importance of various Y groups, the reader will find some deviation from this restriction). Finally, compounds containing a silyl group as the functional group are not considered. An overview of the field of organosilicon chemistry would show that in the last several decades the commercial synthesis of organosilicon products has increased substan­ tially, both in annual production and also in the increasing variety of compounds produced. This increase in the number of commercially available carbon-functional monomers and polymers (silicone polymers) is most remarkable and is occurring because new applications are continually being found for these compounds. As might be expected, the number of publications in this field is also increasing. The important position of silicon in the periodic table - between carbon, aluminum, and phosphorus - means that an understanding of the nature of the bonds in organosilicon compounds is quite important in order to understand the bonding in these other areas.

According to R.H. Crabtree, Metal Dihydrogen and sigma-Bond Complexes is described as `the definitive account of twentieth-century work in the area of sigma complexation'. It covers not only Kubas' discovery of dihydrogen coordination and the study of its structure and general properties but also discusses both the theoretical beliefs and experimental results of bonding and activation of dihydrogen on metal centers and the coordination and activation of C-H, B-H, X-H, and X-Y bonds, giving an overview of `one of the hottest areas in chemistry'.

When presented with a new compound or material, the inorganic chemist will usually have several questions in mind about its composition and structure. Although a simple elemental analysis may answer many questions about its composition, the chemist will still have questions about its structure, and, ifthe material contains a metal atom, he will often want to know its oxidation state, coordination number and geometry. Further, at an increasingly frequent rate, the chemist may need details of the spin­ state, magnetic and perhaps dynamic properties of the material. If the investigator is fortunate, the material or compound may contain an ele­ ment such as iron, tin, antimony, iodine, gold, or one of several of the rare earth metals which are amenable to study by the Mossbauer effect. Often the Mossbauer effect can, sometimes with quite simple experiments, provide the answers to all of these questions. The goal of this book is to illustrate the effectiveness of the Mossbauer effect in providing the answers to the many questions that arise in char­ acterizing new materials and, indeed, in studying known materials in more detail. Several chapters introduce the effect to the novice and provide details about the various hyperfine interactions that are the "bread and butter" of the Mossbauer spectroscopist. Three chapters deal specifically with the experimental aspects of the technique and the increasing impor­ tance of sophisticated computer analysis of the resulting data.

Stability constants are fundamental to understanding the behavior of metal ions in aqueous solution. Such understanding is important in a wide variety of areas, such as metal ions in biology, biomedical applications, metal ions in the environment, extraction metallurgy, food chemistry, and metal ions in many industrial processes. In spite of this importance, it appears that many inorganic chemists have lost an appreciation for the importance of stability constants, and the thermodynamic aspects of complex formation, with attention focused over the last thirty years on newer areas, such as organometallic chemistry. This book is an attempt to show the richness of chemistry that can be revealed by stability constants, when measured as part of an overall strategy aimed at understanding the complexing properties of a particular ligand or metal ion. Thus, for example, there are numerous crystal structures of the Li+ ion with crown ethers. What do these indicate to us about the chemistry of Li+ with crown ethers? In fact, most of these crystal structures are in a sense misleading, in that the Li+ ion forms no complexes, or at best very weak complexes, with familiar crown ethers such as l2-crown-4, in any known solvent. Thus, without the stability constants, our understanding of the chemistry of a metal ion with any particular ligand must be regarded as incomplete. In this book we attempt to show how stability constants can reveal factors in ligand design which could not readily be deduced from any other physical technique.

Focusing on practical applications, the author provides a balanced introduction to the many possible technological uses of metal complexes. Coverage includes the transition metals, lanthanide and actinide complexes, metal porphyrins, and many other complexes. This volume meets the needs of students and scientists in inorganic chemistry, chemical physics, and solid-state physics.

This book represents Volume 2 in a series on the use of Mossbauer spectroscopy in the study of magnetism and materials. However, the perceptive reader will notice some differences from Volume 1. Specifically, in order to market the book at a more affordable price for most universities and research laboratories, the book has been prepared in camera­ ready format The editors and the authors agreed to do this because there is a demand for such a book in the Mossbauer community. This format has placed an extra burden on the editors and the authors and we hope we have overcome all the difficulties generated by the transfer of files between different computers. In order to make the book more attractive to materials scientists who are not experts in Mossbauer spectroscopy, this volume is particularly oriented towards the study of materials by Mossbauer spectroscopy and related complementary techniques, such as neutron scattering and a variety of surface scattering techniques. The authors of this volume can be proud of the high quality professional effort they have devoted to clearly presenting their specific topics. As a result we very much enjoyed working with the authors on this volume. We hope that their effort will help to educate the next generation of Mossbauer effect spectroscopists, a generation which will face the challenge of maintaining equally high scientific and professional standards in their research work.

Organometallic chemistry belongs to the most rapidly developing area of chemistry today. This is due to the fact that research dealing with the structure of compounds and chemical bonding has been greatly intensified in recent years. Additionally, organometallic compounds have been widely utilized in catalysis, organic synthesis, electronics, etc. This book is based on my lectures concerning basic organometallic chemistry for fourth and fifth year chemistry students and on my lectures concerning advanced organometallic chemistry and homogeneous catalysis for Ph.D. graduate students. Many recent developments in the area of organometallic chemistry as weIl as homogeneous catalysis are presented. Essential research results dealing with a given class of organometallic compounds are discussed briefly. Results of physicochemical research methods of various organometallic compounds as weIl as their synthesis, properties, structures, reactivities, and applications are discussed more thoroughly. The selection of tabulated data is arbitrary because, often, it has been impossible to avoid omissions. Nevertheless, these data can be very helpful in understanding properties of organometaIlic compounds and their reactivities. All physical data are given in SI units; the interatomic distances are given in pm units in figures and tables. I am indebted to Professor S. A. Duraj for translating and editing this book. His remarks, discussions, and suggestions are greatly appreciated. I also express gratitude to Virginia E. Duraj for editing and proofreading.

Molecular clusters, in the broad sense that the term is commonly understood, today comprise an enormous class of species extending into virtually every important area of chemistry: "naked" metal clusters, transition metal carbonyl clusters, hydrocarbon cages such as cubane (C H ) and dodecahedrane (C H ), 8 8 20 20 organometallic cluster complexes, enzymes containing Fe S or MoFe S 4 4 3 4 cores, high polymers based on carborane units, and, of course, the many kinds of polyhedral borane species. So large is the area spanned by these diverse classes that any attempt to deal with them comprehensively in one volume would, to say the least, be ambitious-and also premature. We are presently at a stage where intriguing relationships between the various cluster families are becoming apparent (particularly in terms of bonding descriptions), and despite large dif­ ferences in their chemistry an underlying unity is gradually developing in the field. For example, structural changes occurring in Fe S cores as electrons are 4 4 pumped in and out, in some measure resemble those observed in boranes and carboranes. The cleavage of alkynes via incorporation into carborane cages and subsequent cage rearrangement, a sequence familiar to boron chemists, is a thermodynamically favored process which may be related to the behavior of unsaturated hydrocarbons on metal surfaces; analogies of this sort have drawn attention from theorists and experimentalists.