Werners Coordination Theory

Jdrgensen s work on amine displacement constituted the groundwork for Alfred Werner, who showed that, upon further replacement of amines with anions X-, these new substituents also exhibited properties as if bound to the metal atom. Werner concluded that ammonia molecules could not exist in the chains suggested by the Blomstrand-J0rgensen theory and proposed an alternative way of viewing metal ammine bonding. Pfeiffer in 1928 described this transforming event  

According to his own statement, the inspiration (for Coordination Theory) came to him like a flash. One morning at two o clock he awoke with a start the long-sought solution of this problem had lodged in his brain. He arose from his bed and by five o clock in the afternoon the essential points of the coordination theory were achieved. 

2 Werner noted that six ammonia ligands could be arranged around a central metal ion (M) with four different possible geometries. Draw and name these below. 

3 Determine the possible number of isomers for each of your geometries given MA4B2 and MA3B3 formulas and record these below (show your work). 

4 Assuming that two geometric isomers for both formulas exist, Werner predicted 

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Stereoisomers include cis and trans isomers, chiral isomers, compounds with different conformations of chelate rings, and other isomers that differ only in the geometry of attachment to the metal. The study of stereoisomers provided much of the experimental evidence used to develop and defend the Werner coordination theory. X-ray crystallography allows facile elucidation of isomeric structures as long as suitable crystals can be obtained. 

Draw appropriate diagrams of compound (2) in the table, using (i) the Blomstrand-Jorgensen chain theory, (ii) the Werner coordination theory, and (iii) the present method of representing coordination compounds. 

First donor-acceptor adduct (coordination compound) NH3.BF1 prepared by J. L. Gay Lussac (A. Werner s theory, I89I-5). 

Solvates are perhaps less prevalent in compounds prepared from liquid ammonia solutions than are hydrates precipitated from aqueous systems, but large numbers of ammines are known, and their study formed the basis of Werner s theory of coordination compounds (1891-5). Frequently, however, solvolysis (ammonolysis) occurs (cf. hydrolysis). Examples are ... 

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. 

Alfred Werner. His theory of coordination chemistry was published in 1893 when Werner was 26 years old. In his paper Werner made the revolutionary suggestion that metal ions such as Co3+ could show two different kinds of valences. For the compound Co(NH3)eCI3, Werner postulated a central Co3+ ion joined by "primary valences" (ionic bonds) to three Cl- ions and by "secondary valences"... 

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... 

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. 

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... 

Werner s coordination theory25 was a watershed in the history of coordination chemistry and gave the field its name. With a few exceptions, the majority of chemists accepted Werner s views, and most 20th century contributions have been developments, extensions or confirmations of Werner s theory rather than ideas incompatible with or opposed to it. Ley s concept of inner complex salts is one of the earliest of such post-Werner developments.80... 

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. 

The concept of isomerism and isomer counts were used extensively in the development of Werner s theory. They are still important, but on a much more sophisticated level than Werner could have imagined some of the structures which he used are now known to be greatly distorted22 and others are not as simple as he believed. Geometric isomers may exist in one form or another, depending upon the solvent, temperature and other conditions, or they may change their coordination numbers. For example, it has been found that [Co(PEt3)2(NCS)2] is planar in the solid state,... 

It was the optical resolution of [Co(en)2(NH3)Cl]2+ that firmly established Werner s theory and which initiated the study of the optical activity of complex ions. The realization that some octahedral complexes are chiral evidently did not occur to Werner until several years after he published his theory of coordination. He then realized that the demonstration of this property would furnish an almost irrefutable argument in favor of his theory, and he and his students devoted several years to attempts to effect such resolution. Had he but known it, the problem could have been easily solved, for cis-[Co(en)2(N02)2]X (X = Cl, Br) crystallizes in hemihedral crystals which can be separated mechanically, just as Pasteur separated the optical isomers of sodium ammonium tartrate. 

We saw in Section 1.3 how Alfred Werner formulated the modern concept of coordination chemistry, which supramolecular chemistry generalises to a complete coordination chemistry . Prior to Werner s time the chain theory of coordination compounds was popular. The chain and Werner formulations of Co (NIT3) 4CI3 and Co (NH3) 3C13 are shown in Figure 3.1. While both theories predict that Co (NH3) 4C13 will exhibit one labile chloride ion per molecule, the chain theory also predicts that Co(NH3)3C13 will have one labile chloride, while Werner s theory ultimately correctly predicted that the chloride is not labile in this case. 

Octahedral Six Coordinate In addition to the tris-bidentate complexes and the unidentate complexes discussed above, there are many other examples of chiral metal complexes that are based on octahedral geometry. For example, there are a number of reports of edge-sharing binuclear structures containing four bidentate chelates. The individual metal centers in these binuclear species can exist as either A or A enantiomers, and, therefore, the overall structure can be chiral AA and AA, or the achiral (meso) AA pair as illustrated in Figure 5.12a and b. Studies of complexes of this type were important in the proof of Werner s coordination theory. In these pioneering studies, Werner was able to prove by experiment the existence of the three isomers (AA, AA, and AA) of [Co2(p-NH2)( l-NC>2)(en)2]4 +. 23 For Cr(III) complexes, Werner showed that the / >.vo-AA- Cr2(p-OH)2(en)414 1 may be prepared by... 

Koord. Khim. ( Russ. J. Coord. Chem. ) 19(5), 331-408 (1993) (issue dedicated to 100 years of Werner s coordination theory). 

A recent review [440], published 100 years after Werner s coordination theory was first presented, was dedicated to the complex compounds obtained on the basis of polypyrazolyl-borates or scorpionates. Complexes of this kind, an example of which is presented by structure 234, have been obtained with practically all p, /-elements and they can be examined as N-containing analogoues (MN4 coordination unit) of p-diketonates 2 (M04 coordination unit) ... 

Metal complexes (complex compounds or coordination compounds) are one of the most important groups of chemical compounds and form the basis of coordination chemistry. Although complex compounds date back to the 18th century, coordination chemistry was considered a science only after the formulation of the coordination theory by the Swiss chemist A. Werner at the end of the 19th century [1], During the 20th century, thousands of metal complexes were obtained, characterized, and widely applied. Much has been written on heir synthesis, structure, and properties [2-13],... 

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