Studies by Alfred Werner

Chelate complexes of ethylenediamine provide many of the examples on which the theories of coordination chemistry have been founded. Co111 complexes of this ligand were studied by Alfred Werner and his students186 and the separation of or-CoCl(en)2(NH3)2+ into its optical enantiomers187 was a key factor in establishing octahedral stereochemistry. 

The seminal studies on these complex compounds were conducted by Alfred Werner in an intensive period of work at the turn of the century. A typical example of the problems that Werner addressed lies in the various compounds which can be obtained containing cobalt, ammonia and chlorine. Stable and chemically distinct materials with formulations Co(NH3) Cl3 (n = 4,5 or 6) can be isolated. The concepts of valency and three-dimensional structure in carbon chemistry were being developed at that time, but it was apparent that the same rules could not apply to... 

The structural and formulaic questions concerning compounds such as (4.66a)-(4.66c) were largely resolved by Alfred Werner,31 the first inorganic chemist to receive a Nobel Prize (1913). Werner carefully studied the total number of free ions contributing to ionic conductivity, as well as the number of free chloride ions that could be precipitated (exchanged with a more soluble ion) under conditions of excess Ag+, namely... 

These studies reflect the increasing emphasis placed on second coordination sphere influence on the activity and properties of metal complexes, in particular metal-oxo and metal-peroxy species, as proposed by Alfred Werner over a century ago. 

The supersession of the most successful pre-Werner theory of the structure of coordination compounds, the so-called Blomstrand-J0rgensen chain theory, by Alfred Werner s coordination theory constitutes a valuable case study in scientiffc method and the history of chemistry. The highlights of the Werner-J0rgensen controversy and its implications for modem theories of chemical structure are Wretched in this article. 

Metal complexes have characteristic shapes, depending on the metal ion s coordination number. Two-coordinate complexes, such as [Ag(NH3)2]+, are linear. Four-coordinate complexes are either tetrahedral or square planar for example, [Zn(NH3)4]2+ is tetrahedral, and [Ni(CN)4]2 is square planar. Nearly all six-coordinate complexes are octahedral. The more common coordination geometries are illustrated in Figure 20.12. Coordination geometries were first deduced by the Swiss chemist Alfred Werner, who was awarded the 1913 Nobel Prize in chemistry for his pioneering studies. 

The work of Alfred Werner led to a considerable understanding of the stereochemistries of arrangements of ligands. This understanding was reinforced by X-ray diffraction studies of metal complexes, for example, in the determination of the structures of ammonium hexachloroplatinate and chloropalladite, shown in Figure 15.4. In these there are six groups around the metal ion, at an equal distance, rather like a small portion of the sodium chloride structure. 

The reason was the first ever use of curly or curved arrows, in this case to represent tautomerism in A,A-dimethylamino derivatives. While the arrows were not then meant to indicate movement of electrons (as was later universal in the electronic theory of organic reactions), it is most probable that the symbols were adopted by Robert Robinson who, with Watson, worked at British Dyes during World War I123. Arthur Lapworth and Alfred Werner had already used arrows in mechanistic studies, the former perhaps influenced by the inventor of the TNA process, Bernard J. FlUrscheim, who explained benzene substitution patterns in terms of affinity demand , indicated by arrowed bonds124. 

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