Coordination theory

G. B. Kauffman, Alfred Werner Founder of Coordination Theory, Springer, Berlin, 1966, 127 fp. G. B. Kauffman (ed.) Coordination Chemistry A Century of Progress, ACS Symposium Series 565, Washington DC, 1994, 464 pp. 

Werner s coordination theory, 1, 6 Whewellite structure, 6, 849 Wickmanite structure, 6, 849 Wilkinson s catalyst, 6, 239 Wilson s disease, 5, 721 copper, 6,648 removal, 6,769 copper complexes, 2,959 copper metabolism, 6,766 radiopharmaceutical agents, 6,968 Wolfram s red salt, 5,427 Wurzite... 

It may be pointed out that in some structures easily derivable with the coordination theory, such as the rutile structure, the anion arrangement approximates no type of dose-packing whatever. 

The coordination theory and the principles governing coordinated structures provide the foundation for an interpretation of the structure of the complex silicates and other complex ionic crystals which may ultimately lead to the understanding of the nature and the explanation of the properties of these interesting substances. This will be achieved completely only after the investigation of the structures of many crystals with x-rays. To illustrate the clarification introduced by the new conception the following by no means exhaustive examples are discussed. 

As an illustration of the application of the principles in the prediction of structures with the coordination theory, some properties of the structures of the three forms of Al-iSiOs, cyanite, andalusite and sillimanite, are predicted. 

III. Tlie prediction of a structure with the coordination theory. 

By making use of the coordination theory of ionic crystals, I have predicted a structure for topaz which agrees satisfactorily with the experimental data. This structure is described in the following paragraphs. 

The coordination theory, which has been applied successfully2 to brook-ite, the orthorhombic form of titanium dioxide, is based on the assumption that the anions in a crystal are constrained to assume positions about the cations such that they indicate the corners of polyhedra of which the cations mark the centers. These polyhedra are the fundamentally important constituents of the crystal retaining their form essentially, they are combined by sharing corners, edges, and faces in such a way as to build up a crystal with the correct stoichiometrical composition. Thus in rutile, anatase, and brookite there occur octahedra of oxygen ions about titanium ions in rutile each octahedron shares two edges with adjoining octahedra, in anatase four, and in brookite three. 

Noyes himself had been a student of Ostwald. Lewis had spent the academic year 190001 at the institutes of Ostwald and Nernst. Colloquium topics at MIT in the period from roughly 1905 to 1910 included both chemical and physical topics Alfred Werner s coordination theory of valence, tautomerism, and the absolute size of atoms. 

Although authors [74,75] have claimed that a generator-coordinate theory yields an expression for spectral terms exactly of Dunham s form, as in formula 8, in which however term coefficients encompass intrinsically elfects of at... 

Isomerism in the Metal-ammines.—Werner claimed for the coordination theory that in certain cases isomerism should occur, that isomerism being brought about by different causes. lie divided isomerism in the ammines into five groups, namely, structure isomerism, ionisation isomerism, hydrate isomerism, polymerism, and stereoisomerism. 

Claus first postulate was vigorously attacked by Karl Weltzien (1813—1870),40 while Hugo Schiff (1834—1915)43 attacked not only Claus first postulate but also his second. All of Claus three postulates reappeared modified almost four decades later in Werner s coordination theory. Claus third postulate closely adumbrates Werner s concepts of the coordination number and of the transition series between metal ammines and metal salt hydrates. 

Whereas Kekule disposed of complex compounds by banishing them to the limbo of molecular compounds , other chemists developed highly elaborate theories to explain their constitution and properties. The most successful and widely accepted of such pre-Werner theories was the chain theory,47 advanced by Christian Wilhelm Blomstrand (1826-1897)4 and developed by Sophus Mads Jorgensen (1837—1914).46 49 50 Although Werner s ideas eventually triumphed, this did not invalidate Jorgensen s observations. On the contrary, his experiments have proven completely reliable and provided the experimental foundation not only for the Blomstrand—Jorgensen chain theory but also for Werner s coordination theory. 

The circumstances surrounding the creation of Werner s coordination theory provide us with a classic example of the flash of genius . One night in late 1892, Werner awoke at 2 a.m. with the... 

Table 1 shows a comparison of the formulas and predicted numbers of ions for the transition series [Co(NH3)6](N02)3. .. K3[Co(N02)6] according to the two theories, and Figure 1 shows the results of Werner s first published experimental work in support of his coordination theory, a study of conductances carried out in collaboration with his friend and former fellow student Arturo Miolati (1869—1956).63... 

In their first publication on this subject,59 Werner and Miolati showed that the molecular conductances (fx) of coordination compounds decreased as successive molecules of ammonia were replaced by acid residues (negative groups or anions). For cobalt(III) salts, they found that fi for luteo salts (hexaammines) > fi for purpureo salts (acidopentaammines) > /t for praseo salts (di-acidotetraammines). The conductance fell almost to zero for the triacidotriammine Co(N02)3-(NH3)3 and then rose again for tetracidodiammines, in which the complex behaved as an anion. By such measurements, Werner and Miolati determined the number of ions in complexes of cobalt(III), platinum(II) and platinum(IV). They not only found support for the coordination theory, but they also elucidated the process of dissociation of salts in aqueous solution and followed the progress of aquations. 

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... 

Even so great an admirer of Werner as Paul Pfeiffer (1875-1951),93 Werner s former student and one-time chief of staff at the University of Zurich and the man who first applied Werner s theory to crystal structures (see Section 1.1.5.4), proposed modifications of the coordination theory. He applied what he called the principle of affinity adjustment of the valencies to overcome certain shortcomings of Werner s theory.94 He considered the ionizable radicals or atoms in the outer sphere to be combined with the complex radical as a whole and not attached definitely to the central atom or to any of its associated molecules. He also applied this idea to complex organic molecular compounds. However, Pfeiffer s modifications should not be interpreted as attacks on Werner s ideas. 

Werner apparently did not realize that the polynuclear complexes which he investigated so extensively95 constituted a transition between the usual mononuclear coordination compounds and the infinite structure of the crystal lattice. It remained for Paul Pfeiffer, Paul Niggli (1888—1953) and others to point out that crystal structures were in beautiful agreement with his coordination theory, as revealed by the then new experimental technique of X-ray diffraction.96... 

Since Dickinson s first determinations, crystal structures of many other complexes of various coordination numbers have been determined. All these investigations and others have provided a complete and direct confirmation of Werner s views to support his indirect configurational proofs obtained during the previous decades by preparation of isomers and resolution of optically active compounds (see Section 1.1.4), and today the terminology and concepts of coordination theory are routinely used in crystallography. 

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