Wemer, Alfred

Kauffman, Alfred Wemer-Founder of Coordination Chemistry. 

Kauffman, G. B. Alfred Wemer, Founder of Co-ordination Chemistry. Springer Berlin, Heidelberg, New York 1966... 

As new complex ions were synthesized, several bonding theories were postulated and rejected. The two most convincing theories, the Blomstrand-Jorgensen chain theory and coordination theory proposed by Alfred Werner, were debated extensively (a subject taken up in detail in Chapter 2) and it was coordination theory that eventually proved to be correct, winning Wemer the Nobel Prize in 1913. 

Alfred Wemer (1866—1919). Swiss chemist. Werner started as an organic chemist hut hecame interested in coordination chemistry. For his tiieory of coordination compounds, Werner was awarded the Nobel Prize in Chemistry in 1913. 

But Kekuld s stability criterion, or to be more accurate, instability criterion failed completely in the case of many coordination compounds, especially the metal-ammines, which were classified as molecular compounds by sheer dint of necessity even though they were extremely resistant to heat and chemical reagents. For example, look at Figure 1. Although hexaamminecobalt(III) chloride contains ammonia, it neither evolves this ammonia on mild heating nor does it react with acids to form ammonium salts. Also, despite its cobalt content, addition of a base to its aqueous solution fails to precipitate hydrated cobalt(III) hydroxide. It remained for Alfred Werner to explain successfully the constitution of such compounds, but the time was not yet ripe. Before considering Werner s coordination theory, we must examine one more theory of coordination compounds, perhaps the most successful of the pre-Wemer theories, namely, the Blomstrand-J0rgensen chain theory. 

Alfred Werner conjectured as early as 1899 that octahedrally coordinated metal complexes should occur in nonidentical minor image isomers. For such objects. Lord Kelvin, in 1893, had coined the adjective chiral , a term never used by Werner. It can be proved by examination of the original sample of [Co(NC)2)2(en) Br, prepared by Edith Humphrey, a Ph.D. student of Wemer s, that crystals of optically pure samples were obtained in Werner s laboratory as early as 1899 or 1900. However, Werner did not publish die first successful resolution of an octahedral metal complex until 1911. Presently, interest in chirality in coordination compounds is booming, mainly because of the importance of coordination compounds in enantioselective homogeneous catalysis. Other interesting sq )plications are enantioselective interactions of chiral coordination species with biomolecules, and the stereoselective synthesis of multicenter systems. 

D.H. Busch, Helv. Chim. Acta, Ease. Extraord., Alfred Wemer (1866-1919), 1967, 174. 

The basic explanation for the structure of these complexes was given by the Swiss chemist Alfred Werner in 1893. According to Wemer, a metal atom exhibits two kinds of valences, a primary valence and a secondary valence. The primary valence is what we now call the oxidation number of the metal. The secondary valence corresponds to what we now call the coordination number, which is often 6. In Werner s view, the substance previously represented by the formula PtCl4 6NH3 is composed of the ion Pt(NH3)6", with six ammonia molecules directly attached to the platinum atom. The charge of this ion is balanced by four Cl ions, giving a neutral compound with the structural formula [Pt(NH3)6]Cl4. 

However, in 1890, a young Swiss chemist named Alfred Werner, who had just obtained a Ph.D. in the field of organic chemistry, became so interested in these compounds that he apparently even dreamed about them. In the middle of one night Wemer awoke realizing that he had the correct... 

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