Tuesday, March 11, 2014

Alfred Werner and Inorganic Chemistry

According to The Nobel Prize website, nine chemists have been awarded Nobel Prizes in chemistry for their works in Inorganic Chemistry. In 1913, Alfred Werner was awarded the prize for  "... 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." 

Alfred Werner was born in Mulhausen-Alsace (German land back then) in 1866. When he was in military, he attended some chemistry lectures in a high school. Then, he went on studying chemistry and did his Ph.D. under the guidance of Arthur Hantzsch in organic chemistry! The title of his thesis was "Über räumliche Anordnungen der Atome in stickstoffhaltigen Molekülen" ("On spatial arrangements of atoms in nitrogen-containing molecules"). After a few years, he started to work in University of Zurich where he later accepted Swiss nationality. He was teaching organic chemistry and doing research in stereochemistry of nitrogen-containing molecules, but he became increasingly interested in coordination compounds and inorganic chemistry. He synthesized several ammonia complexes of Cobalt(III). 

In his Nobel lecture, Alfred Werner said:

"During the great era of development of organic chemistry, during which the theory of structure was perfected, the molecular compounds had become stepchildren, and attention only continued to be given to a few of them because they were of practical interest. This neglect can be ascribed to the fact that it was impossible to develop the constitution of these compounds on the same valence principle as the constitution of organic compounds."

Although molecules like NH4+, PCl5 were known, chemists like Kekule, suggested that there could only be one "valence" (oxidation state) of a given element. For example, Kekule suggested that PCl5 is in fact PCl3.Cl2 . This dot notation is still used although it does not give any structural information (CuSO4.5H2O, IrCl3xH2O etc.). 

Werner was both a great theorist and an experimentalist. He was certain of the existence of the isomers of his metal complexes. So, he went on drawing the possible isomers for a six-coordinate model complex and finally suggested that the complexes had octahedral geometries. He supported his suggestion by some observations.

Of course, like Kekule, there were other chemists that thought the oxidation state is fixed and the bonding had to be like these:

(You can find more on the discussions why these were wrong here or here in his Nobel lecture.)

Finally, he was able to introduce a new geometry, isomers and the possibility of having a different Hauptvalenz (oxidation state) than Nebenvalenz (coordination number). He also made some contributions to the final "shape" of the periodic table. He arranged the known elements of his time and left space for lanthanides and actinides understanding that they were "different" without knowing any quantum chemistry.

In almost every inorganic chemistry textbook and article on inorganic and coordination chemistry, you can see Alfred Werner's and his complexes' name repeatedly (Werner Complexes, anti-Werner Complexes etc.) and I think it is right to call him as the "father of modern inorganic/coordination chemistry.
He wrote almost two hundred articles and two books; Lehrbuch der Stereochemie ("Textbook of Stereochemistry") and Neuere Anschauungen auf dem Gebiete der anorganischen Chemie ("New Ideas in Inorganic Chemistry"). You can read them in German both online and free here and hereLehrbuch der Stereochemie was dedicated to his Ph.D. advisor Arthur Hantzsch.

No comments:

Post a Comment