The Foundation of Coordination Chemistry

Before we travel too far, however, it may be valuable to look back to the beginnings of coordination chemistry. While examples of coordination compounds were slowly developed during the nineteenth century, it wasn t until the twentieth century that the nature of these materials was understood. They were at a very early stage named complex compounds , a reflection of their unexplained structures, and we still call them complexes today. Around the beginning of the twentieth century, the wealth of instrumental methods we tend to take for granted today simply didn t exist. Chemists employed chemical tests, including elemental analyses, to probe formulation and structure, augmented by limited physical measurements such as solubility and conductivity in solution. Analyses defined the components, but not their structure. As a consequence, it became usual to represent 

This type of what we now consider simple experiments provided a foundation for coordination chemistry as we now know it. What became compelling following the discovery of these intriguing compounds was to develop a theory that would account for these 

Original Formulation Current Representation Number of Ions Experimental Results 

Identifying ionic composition from molar conductivity experiments for a series of platinum(IV) complexes of ammonia and chloride ion. 

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The term classical complexes is used here for want of a better one. We are attempting to designate those complexes that can, for the most part, be described in terms of (1) a set of ligands with a discrete electron population, and (2) a metal atom with a well-defined oxidation number. In a general way classical complexes are of the type that Werner dealt with in laying the foundations of coordination chemistry, as contrasted with other types that have more complicated behavior. 

Althougt J0rgensen was defeated by Werner, his experimental contribution to the foundation of coordination chemistry cannot be denied. Jensen was well acquainted with J0rgensen s work and often referred to it Some of the compounds prepared by J0rgensen apparently have not found their final formulation in Werner s system. 

With these three concepts, fixation, recognition and coordination, the foundations of supramolecular chemistry are laid. Why did it take so long to come to life Molecular associations have been recognized and studied for a long time [1.14] and... 

Werner s coordination theory, with its concept of secondary valence, provides an adequate explanation for the existence of such complexes as [Co(NH3)6]Cl3-Some properties and the stereochemistry of these complexes are also explained by the theory, which remains the real foundation of coordination chemistry. Since Werner s work predated by about twenty years our present electronic concept of the atom, his theory does not describe in modem terms the nature of the secondary valence or, as it is now called, the coordinate bond. Three theories currently used to describe the nature of bonding in metal complexes are (1) valence bond theory (VBT), (2) crystal field theory (CFT), and (3) molecular orbital theory (MOT). We shall first describe the contributions of G. N. Lewis and N. V. Sidgwick to the theory of chemical bonding. 

In 1923, Gilbert Newton Lewis defined an acid as an electron pair acceptor and a base as an electron pair donor. This definition is even more inclusive than the previous one because it includes all Bronsted-Lowry acids and bases as a subset and provides the foundation for the field of coordination chemistry. A coordination compound is the product of a Lewis acid-base reaction, such as the one shown in Equation (14.11) and Figure 14.5, in which the metal ion (Lewis acid) and ligand (Lewis base) are held together by a coordinate covalent bond. 

We would like to thank the National Natural Science Foundation of China and the State Key Laboratory of Coordination Chemistry at Nanjing University for financial support. 

YJ hile Wemer s classic paper 49) of 1891 can be regarded as the foundation of modern inorganic coordination chemistry, it has been only during the past 10 to 15 years that a rationalization of the many stereochemistries possible for a coordination complex has become possible— through the modern techniques of spectroscopy and magnetism. Even today, however, many problems remain to be solved, and it is the purpose of this review to outline some of these difficulties. 

In 1893, Alfred Werner proposed the coordination theory and demonstrated that stereochemistry is not limited to carbon compounds, but is a general phenomenon encompassing metal coordination compounds. This epoch-making theory not only succeeded in systematizing the transition-metal complexes but also afforded the foundation of modem structural inorganic chemistry. 

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). 

The first task of chemoinformatics is to transform chemical knowledge, such as molecular structures and chemical reactions, into computer-legible digital information. The digital representations of chemical information are the foundation for all chemoin-formatic manipulations in computer. There are many file formats for molecular information to be imported into and exported from computer. Some formats contain more information than others. Usually, intended applications will dictate which format is more suitable. For example, in a quantum chemistry calculation the molecular input file usually includes atomic symbols with three-dimensional (3D) atomic coordinates as the atomic positions, while a molecular dynamics simulation needs, in addition, atom types, bond status, and other relevant information for defining a force field. 

The resolution of optically active coordination compounds, a feat which shook chemistry to its innermost foundations ,72 gained for the coordination theory the widespread recognition for which Werner had been striving for so long. Nor was the theory s founder neglected, for two years later, largely in recognition of the most brilliant confirmation of [his] stereochemical views ,73 Werner was awarded the Nobel Prize in chemistry for 1913.74... 

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