Alfred Werner

Founder of Coordination Chemistry

 

Alfred Werner (1866 - 1919)

Until the appointment of Werner the main emphasis of chemical research at the University had been in organic chemistry. The doctoral work of Werner was concerned with the chemistry of aromatic compounds, although after his appointment as professor he held classes in both organic and inorganic chemistry, as well as stereochemistry. His lectures were extremely popular, and attracted large numbers of students, including also foreign diploma and doctoral students. The growing number of students and the rather dismal condition of the chemistry building at that time created a strong pressure for new facilities, and in 1905 the cantonal government put forward plans for a new chemistry building, which was completed in 1909 at Rämistrasse 74/76. This was to be the main home of the Chemistry Institutes of the University until the opening of the new Irchel campus in 1978. The most important scientific work of Werner, which led directly to the award of the Nobel Prize in 1913, was concerned with the structure and coordination theory of transition metal-amine complexes. Around the end of the last century the understanding of valence bonding and geometry in metal-amine complexes such as [Co(NH₃)₆Cl₃] was in a confused state. This can be readily appreciated by comparing some generally accepted formulae of that time with those postulated by Werner. The use of trivalent cobalt, pentacoordinate nitrogen and the assumption that only halogen bound to nitrogen can be easily exchanged, underpinned the acceptance of these early formulae. The suggestion from Werner that these complexes were based on an octahedral array of ligands coordinated to a central metal ion was, at that time, not well accepted. The most powerful evidence in favour of this new formulation came from stereochemical studies. Consider, for example, the three formulae 1-3 shown below, each with 6 ligands arranged around a central metal ion. In the case of [MeB₂A₄l with the geometry of 1 or 2 there would be three possible isomers, but only two if the correct structure was 3. The available experimental evidence had never revealed the existence of more than two such isomers. Of special importance for the acceptance of an octahedral geometry was the isolation of the cis- and trans-isomers of the salts 4 and 5, which had been predicted to occur, but had not previously been discovered. A result of wider significance, however, was the separation of the two predicted enantiomers of [Co(NH₂CH₂CH₂NH₂)₂ClNH₃]²⁺ 2X^- (6) as well as of 7.

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The resolution of these racemates was beautifully in accord with the octahedral geometry of the complexes, but the impact these results had in the chemical community was enhanced by the fact that,at this time, there were still some who clung to the half mystical belief that optical activity was somehow a special property associated with life and the asymmetric carbon atom. Any lingering doubts were completely dispelled by Werner in 1914 with the resolution of the 'inorganic' tetranuclear cobalt complex 8 into its two enantiomeric forms. A successor wrote of Werner:

'Werner's coordination theory has been a guiding principle in inorganic chemistry and in the theory of valence since its publication sixty years ago. Indeed, it might have been said to underline our modern concepts of molecular structure. The current theories of acidity, basicity, amphoterism and hydrolysis grew directly from it...'