Alfred Werner

For the American coach, physical education professor, and college athletics administrator, seeAlfred C. Werner.

Alfred Werner(12 December 1866 – 15 November 1919) was a Swisschemistwho was a student atETH Zurichand a professor at theUniversity of Zurich.He won theNobel Prize in Chemistryin 1913 for proposing theoctahedralconfiguration oftransition metalcomplexes. Werner developed the basis for moderncoordination chemistry.He was the firstinorganic chemistto win the Nobel Prize, and the only one prior to 1973.

Alfred Werner
Werner circa 1915
Born	12 December 1866 Mulhouse,Haut-Rhin,Alsace,France
Died	15 November 1919(1919-11-15)(aged 52) Zürich,Switzerland
Nationality	Swiss (from 1895) French
Alma mater	University of Zurich ETH Zurich
Known for	Configuration oftransition metalcomplexes
Spouse	Emma Werner
Awards	Nobel Prize for Chemistry(1913)
Scientific career
Fields	Inorganic chemistry
Institutions	University of Zurich
Doctoral advisor	Arthur Rudolf Hantzsch,Marcellin Berthelot

Biography

Werner was born in 1866 inMulhouse,Alsace(which was then part of France, but which was annexed by Germany in 1871). He was raised asRoman Catholic.He was the fourth and last child of Jean-Adam Werner, a foundry worker, and his second wife, Salomé Jeannette Werner, who originated from a wealthy family.He went to Switzerland to study chemistry at theSwiss Federal Institute (polytechnikum) in Zurich.Still, since this institute was not empowered to grant doctorates until 1909, Werner received a doctorate formally from the University of Zürich in 1890.After postdoctoral study inParis,he returned to the Swiss Federal Institute to teach (1892). In 1893 he moved to theUniversity of Zurich,where he became a professor in 1895. In 1894 he became a Swiss citizen.

In his last year, he suffered from a general, progressive, degenerativearteriosclerosis,especially of the brain, aggravated by years of excessive drinking and overwork. He died in a psychiatric hospital inZürich.

Werner died on 15 November 1919 ofarteriosclerosisin Zürich at the age of 52.

Research

Coordination chemistry

In 1893, Werner was the first to propose correct structures for coordination compounds containingcomplex ions,in which a central transition metal atom is surrounded by neutral or anionicligands.

For example, it was known that cobalt forms a "complex" hexamine cobalt (III) chloride, with formula CoCl₃•6NH₃,but the nature of the association indicated by the dot was mysterious. Werner proposed the structure[Co(NH₃)₆]Cl₃,with the Co³⁺ion surrounded by six NH₃at the vertices of an octahedron. The three Cl⁻are dissociated as free ions, which Werner confirmed by measuring theconductivityof the compound in an aqueous solution, and also by chloride anion analysis using precipitation withsilver nitrate.Later,magnetic susceptibilityanalysis was also used to confirm Werner's proposal for the chemical nature of CoCl₃•6NH₃.

cis-[Co(NH₃)₄Cl₂]⁺

trans-[Co(NH₃)₄Cl₂]⁺

For complexes with more than one type of ligand, Werner succeeded in explaining the number ofisomersobserved. For example, he explained the existence of two tetramine isomers, "Co(NH₃)₄Cl₃",one green and one purple. Werner proposed that these are twogeometric isomersof formula [Co(NH₃)₄Cl₂]Cl, with one Cl⁻ion dissociated as confirmed by conductivity measurements. The Co atom is surrounded by four NH₃and two Cl ligands at the vertices of an octahedron. The green isomer is "trans" with the two Cl ligands at opposite vertices, and the purple is "cis" with the two Cl at adjacent vertices.

Werner also prepared complexes withoptical isomers,and in 1914 he reported the first syntheticchiralcompound lacking carbon, known ashexolwith formula [Co(Co(NH₃)₄(OH)₂)₃]Br₆.

Nature of valence

Before Werner, chemists defined thevalenceof an element as the number of its bonds without distinguishing different types of bonds. However, in complexes such as [Co(NH₃)₆]Cl₃for example, Werner considered that the Co-Cl bonds correspond to a "primary" valence of 3 at long distance, while the Co-NH₃bonds which correspond to a "secondary" or weaker valence of 6 at shorter length. This secondary valence of 6 he referred to as thecoordination numberwhich he defined as the number of molecules (here of NH₃) directly linked to the central metal atom. In other complexes, he found coordination numbers of 4 or 8.

On these views, and other similar views, in 1904Richard Abeggformulated what is now known asAbegg's rulewhich states that the difference between the maximum positive and negativevalenceof anelementis frequently eight. This rule was used later in 1916 whenGilbert N. Lewisformulated the "octet rule"in hiscubical atomtheory.

In modern terminology, Werner's primary valence corresponds to theoxidation state,and his secondary valence is calledcoordination number.The Co-Cl bonds (in the above example) are now classed as ionic, and each Co-N bond is acoordinate covalent bondbetween theLewis acidCo³⁺and theLewis baseNH₃.

Works

• Lehrbuch der Stereochemie.Fischer, Jena 1904Digital editionby theUniversity and State Library Düsseldorf

References

• W. Gregory Jackson; Josephine A. McKeon; Silvia Cortez (2004). "Alfred Werner's Inorganic Counterparts of Racemic and Mesomeric Tartaric Acid: A Milestone Revisited".Inorg. Chem.43(20): 6249–6254.doi:10.1021/ic040042e.PMID15446870.
• Kristin Bowman-James(2005). "Alfred Werner Revisited: The Coordination Chemistry of Anions".Acc. Chem. Res.38(8): 671–678.doi:10.1021/ar040071t.PMID16104690.

External links

• Alfred Werneron Nobelprize.orgincluding the Nobel Lecture, 11 December 1913On the Constitution and Configuration of Higher-Order Compounds
• The Nobel Prize in Chemistry 1913- short article about his work on the linkage of atoms in molecules by which he has thrown new light on earlier investigations and opened up new fields of research, especially in inorganic chemistry.