Coordination chemistry basic concepts

According to these basic concepts, molecular recognition implies complementary lock-and-key type fit between molecules. The lock is the molecular receptor and the key is the substrate that is recognised and selected to give a defined receptor—substrate complex, a coordination compound or a supermolecule. Hence molecular recognition is one of the three main pillars, fixation, coordination, and recognition, that lay foundation of what is now called supramolecular chemistry (8—11). 

In previous chapters, we have presented a great deal of information about structure and bonding in coordination compounds. This chapter will be devoted to describing some of the important chemistry in the broad areas of organometallic complexes and those in which there are metal-metal bonds. The body of literature on each of these topics is enormous, so the coverage here will include basic concepts and a general survey. 

The discussion assumes a familiarity with the basic concepts of transition metal coordination chemistry, as outlined for example in d- and f-Block Chemistry (C. J. Jones, RSC Tutorial Chemistry Texts 4). 

Platinum is found in compounds having a smaller range of oxidation states than is the case for many of the earlier elements in the periodic table. The differences between it and Pd are somewhat more marked than for analogous pairs of earlier elements. The coordination numbers see Coordination Numbers Geometries) tend to be lower than for earlier elements a CN of six is rarely exceeded and a CN of four is common. Many important concepts in coordination chemistry, such as square-planar coordination and the trans effect, were first discovered in Pt complexes. The high electronegativity of the element is reflected in a poor 7t-basic character, which helps account for the lack of a binary carbonyl. 

It follows from basic concepts that ligand design in Ln chemistry, to impart specific oxidation states, coordination numbers and geometries for future exploitation, has to be extremely well considered. Important attributes of Ln chemistry to consider when designing ligands are summarized as ... 

ASTM Saul Patai s book "The Chemistry of Peroxides" (41) was reviewed with some hope of finding either a systematic evaluation of reactivity as it relates to the potential hazard of peroxides or some basic concepts that would allow formulation of a unifying theory that would permit an algorithmic solution to the classification problem. Unfortunately, when Saul got to the chapter on safety he acknowledges that he gave up. Bretherick s "Handbook of Reactive Chemical Hazards" (42) presents some useful information and incident histories, but provides little in the way of coordinated insight based on molecular composition and structure to allow for systematic extrapolation to new materials. 

Bond - Coordinate Bond . Maybe it doesn t exactly roll off the tongue, but it s hard to avoid this adaptation of the personal introduction used by perhaps our best-known and most enduring screen spy to introduce this section - it serves its purpose to remind us of the endurance and strength of bonds between metals and ligands, which at a basic level we can consider as a covalent bond. Moreover, it isn t just any bond, but a specially-constructed coordinate bond - hence the name of this field, coordination chemistry. Unfortunately, the simple covalent bonding concept does not provide valid interpretations for all of the physical properties of coordination complexes, and more sophisticated theories are required. We shall examine a number of bonding models for coordination complexes in this chapter. 

Metal-containing coordination compounds that show a capacity to cure or control a disease have grown remarkably in number and range of applications in recent decades. Their form covers a wide range of metal ions, ligands and stereochemistries. Some examples appear in Table 9.1. It is not the role of an introductory text to cover applications in depth, but it is appropriate to illustrate their applications and show how they link with our basic concepts of coordination chemistry. 

What we hope is clear from all of the above is that all three approaches require some basic knowledge of aspects of coordination chemistry to extract the full information from the names this is, of course, an inevitability of any language - some concepts of context and unspoken rules are necessary. 

Inherently, whether a coordination compound involves metal or metalloid elements is immaterial to the basic concept. However, one factor that distinguishes the chemistry of the majority of metal complexes is an often incomplete d (for transition metals) or f... 

The mechanisms of surface chemical reactions represent a problem in coordination chemistry, which is the study of complexes, molecular units comprising a central group surrounded by other atoms in close association. This book is principally an introduction to the interpretation of surface phenomena in soils from the point of view of coordination chemistry. Therefore the basic concept to be discussed is the surface functional group, the central moiety in surface complexes, whose formation provides the most important mechanism of adsorption by the solid phases in soils. No detailed consideration of adsorption isotherm equations or the thermodynamic theory of ion exchange is presented, except insofar as their tenuous relation with surface coordination chemistry is to be illustrated. The discussion in this book is intended to be self-contained, but a previous exposure to soil physical chemistry, soil mineralogy, and the fundamentals of inorganic chemistry will prove helpful. 

The nature and properties of metal complexes have been the subject of important research for many years and continue to intrigue some of the world s best chemists. One of the early Nobel prizes was awarded to Alfred Werner in 1913 for developing the basic concepts of coordination chemistry. The 1983 Nobel prize in chemistry was awarded to Henry Taube of Stanford University for his pioneering research on the mechanisms of inorganic oxidation-reduction reactions. He related rates of both substitution and redox reactions of metal complexes to the electronic structures of the metals, and made extensive experimental studies to test and support these relationships. His contributions are the basis for several sections in Chapter 6 and his concept of inner- and outer-sphere electron transfer is used by scientists worldwide. 

Coordination Chemistry is primarily concerned with metal complexes but many of its concepts are applicable to chemistry in general. Students just starting to study chemistry, therefore, will profit Ifom an appreciation and understanding of the basic principles of coordination chemistry, which may be applied in more sophisticated fashion in advanced courses. 

The basic concept of the most common form of electrochemical investigation of the redox chemistry of a coordination compound is that voltammetric data are initially collected and a mechanism for the half-cell reaction that occurs at the working electrode is postulated. A simple process, often used as a voltammetric reference potential standard, would be (Equation (1)) oxidation of ferrocene (Fc) to the ferrocenium cation (Fc ) in an organic solvent (acetonitrile, dichloromethane, etc.) containing 0.1 M of an electrolyte such as BU4NPF6 (added to lower the resistance) ... 

There is little doubt that as a pedagogic tool for introducing coordination chemistry, symmetry, and spectroscopy, LFT will remain a valuable part of the undergraduate syllabus. As such, many of the basic concepts derived from LFT will remain in service. However, the methodology of LFT... 

At least three factors will be operative in determining the net effect of the competitive reactions that establish the chemical form of the chromium and in consequence its biological availability the relative coordinating tendencies of the ligands, and relative affinities of other substances, for chromium(III) the concentrations, and more specifically, the relative ratios of concentrations of the competing reactants to that of chromium(III) the relative rates of reactions. Thus, a problem in nutrition gives rise to a problem involving the basic concepts of coordination chemistry. 

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