Aspects of at UZH from Werner to the Present Day CHIMIA 2009, 63, No. 9 541 doi:10.2533/chimia.2009.541 Chimia 63 (2009) 541–544 © Schweizerische Chemische Gesellschaft Old and New ‘Anschauungen in der ­Anorganischen Chemie’ A Homage to Alfred Werner’s Book and ­Intuition

Part I. Alfred Werner’s Book and Coordination Theory

Heinz Berke*

Abstract: Alfred Werner (1866–1919) is regarded as the founder of coordination chemistry. He was the author of the book entitled ‘Neuere Anschauungen auf dem Gebiete der Anorganischen Chemie’ (New Perspectives in ) which guided generations of in research and teaching. This book was recently awarded the ‘Citation for Chemical Breakthrough’ prize from the Division of the of the Ameri- can Chemical Society. This article is the first of three dedicated to Werner’s life and works. Keywords: Coordination theory · History of Chemistry · Werner, A.

Preface Werner’s book and the ‘Citation for ous to claim that Alfred Werner’s concepts Chemical Breakthrough’ Award of of coordination chemistry have reached Alfred Werner (1866–1919) was a chem- the American Chemical Society eternal validity. Certainly quite a few as- ist of great intuitive capability. Based on pects did survive, and others only in parts. this ability and his great chemistry accom- At the occasion of the yearly Sympo- In conjunction with this the quite stringent plishments at the University of , he sium of the Chemical Society of Zurich, question can be posed of what has remained is regarded as the founder of coordination December 3, 2009, the Division of History valid from his ‘Anschauungen’. This article chemistry. Alfred Werner wrote a book on of Chemistry of the American Chemical in three parts will try to find an answer to coordination chemistry, which not only Society honored the Fachbereich Chemie this question. At the moment we can say that comprised the state of the art, but also its of the with the plaque there are only very few concepts of early conceptual background during the years of modern times chemistry, meaning of those 1900 to 1920. This book guided genera- ‘Citation for Chemical Breakthrough’ of the 19th century, which have survived to tions of chemists in research and teaching the same extent as Alfred Werner’s concepts. and thus gained enormous importance for to commemorate the outstanding achieve- This article will therefore try to review his the chemistry developments. Therefore ment of Alfred Werner’s book (Fig. 1): concept and put them into the perspective of this book was recently awarded the ‘Cita- the present times. Alfred Werner’s approach tion for Chemical Breakthrough’ prize from ‘Neuere Anschauungen auf dem Gebiete to coordination chemistry was actually one the Division of the History of Chemistry der Anorganischen Chemie’ of the first conceptual approaches of chem- of the American Chemical Society http:// istry, where ‘theory’ came to some extent www.scs.uiuc.edu/~mainzv/HIST/awards/ Alfred Werner’s outstanding contribu- before ‘experiment’. As we will see later citations_chem-breakthroughs.php. In ap- tions to coordination chemistry were also Alfred Werner’s ‘theory’ was laid down as preciation of this honour and in allusion to honored with the [1] and numer- early as 1893, so really at the beginning of Werner’s book this personal account of the ous biographical reviews[2] and articles on his work in coordination chemistry. Alfred author was created. It will appear in three Alfred Werner’s coordination chemistry,[3] Werner’s book is the expression of Alfred parts: Part I reviews Alfred Werner’s book which paid adequate credit to the great Werner’s conceptual imagination and just and coordination theory; Parts II and III will achievements of the “founder of coordi- from this point of view, it indeed deserves give examples of Alfred Werner’s intuition nation chemistry”. The plaque praises the the consideration, the awareness, given by by aid of contemporary studies of complex- book’s main theme, which is a chemical the American Chemical Society with this es from the Werner Collection of original concept: award. samples of the University of Zurich. “The concept of coordination com- But Alfred Werner’s book should be ac- pounds: How ions and groups of atoms knowledged in other respects, since it had bind and arrange around a central metal great impact on 100 years of developments atom in three dimensions” in chemistry. His ‘Anschauungen’ were Early concepts of chemistry did not the foundation for progress in coordina- *Correspondence: Prof. Dr. H. Berke Anorganisch-Chemisches Institut normally survive for a period of over 100 tion chemistry research and its branching Universität Zürich years, as they adopted progress in the field out into adjacent areas and became thus Winterthurer Str. 190 and were thus often subjected to changes. also a base for the interdisciplinary devel- CH-8057 Zürich E-mail: [email protected] It would be quite arrogant and presumptu- opments of this field. 542 CHIMIA 2009, 63, No. 9 Aspects of Chemistry at UZH from Werner to the Present Day

in the subject in guided by his school teacher. His main chemistry endeav- ors started with his enrollment as student at the ETH Zürich in 1887. He then made a PhD thesis with Professor Hantzsch, a pio- neering pyridine . After he received the ‘call’ to the University of Zurich as an associate professor in 1893 he made contact with Professor A. Miolati from Turin, from whom he learned to carry out conductivity measurements, which in its essence is a very effective analytical tool for ‘counting’ ions of complexes in solution helping greatly to unravel their ‘constitution’ of complexes. His inspiration for the ‘Constitution of In- organic Compounds’ (complexes) came suddenly as a ‘flash of genius’ in late 1892. Fig. 1. Left: Picture of Alfred Werner’s book ‘Neuere Anschauungen auf dem Gebiete der The following is reported: Anorganischen Chemie’, which appeared in the series ‘Die Wissenschaft. Einzeldarstellungen aus For one night in late 1892 Alfred Werner der Natur, Wissenschaft und Technik’, Friedrich Vieweg & Sohn, Braunschweig: First edition 1905, awoke at 2 a.m. with the solution of the con- 2nd edition 1909, 3rd edition 1913, 4th edition 1920, 5th edition 1923. The 5th edition appeared stitution of ‘molecular compounds’, which after Werner’s death and was edited by Professor P. Pfeiffer, University of Bonn, Germany had come to him like a flash of lightning. He (Professor P. Pfeiffer was a ‘Dozent’ at the Chemisches Institut of the University of Zurich, later arose from his bed and wrote furiously and professor of chemistry at the University of Bonn). Right: Picture featuring the presentation of the without interruption. By 5 p.m. of the fol- plaque award of the Division of History of the American Chemical Society (HIST). Professor H. lowing day he had finished his most famous Berke, receiving the plaque in the name of the Fachbereich Chemie of the University of Zurich paper titled: ‘Contribution to the Constitu- (left) and Professor D. Arigoni, ETH Zürich, American Chemical Society delegate handing the plaque over (right). tion of Inorganic Compounds’, A. Werner, Zeitschrift für Anorganische Chemie 1893, 2, 267. He was already full professor at the time Immediately after the book’s first ap- sonal and amusing way, finding the an- when the first edition of his book appeared pearance in 1905 and 12 years after Alfred ecdotal origins of some ideas that have in 1905. His chemistry endeavors reached a Werner’s legendary publication on co- modern implications and applications. first peak in the understanding of complexes ordination theory, Alfred Werner’s book Over the years the author has investigat- as stereochemical three-dimensional mol- advanced to the main guide in the field ed, or more accurately, has reinvestigated ecules possessing a special binding mode of coordination chemistry. It was supple- some of the original samples of the Werner different from those of organic chemistry. mented in four more editions maturing group compiled in the collection of original A great event and maybe also another in- through the years till 1923. In this period samples at the University of Zurich. The spirational push to his research came when of time, this book not only functioned main impetus for this came from the idea he and his group moved to the new chemis- as a compendium with comprehensive to create an impression of Alfred Werner’s try building in Rämistrasse in 1909, which coverage of descriptive phenomenologi- intuition. Intuition is based on imagination, celebrates its centennial this year. This cal coordination chemistry, but indeed inspiration and knowledge and accord- move apparently gave support to another also documented the state of the art of ing to Werner’s contemporary Albert Ein- peak of scientific achievement: the discov- the theoretical and conceptual knowledge stein, imagination is more important than ery of the chirality of complexes. The first in the field. Needless to say at the time knowledge. Alfred Werner’s book indeed optical resolution of complexes was carried the leading views were those of Alfred witnesses in a unique way comprehensive out in 1911 by his American coworker V. Werner, putting coordination chemistry knowledge of the turn of the century. With L. King and the first chiral separation of on solid ground. Alfred Werner’s input Einstein’s correct assessment in mind we a non-carbon containing purely inorganic was so enormous in quantity and quality feel it too boring to survey a time’s knowl- complex was accomplished in 1913 by Al- that it has retained validity even a hun- edge; rather we would like to trace Werner’s fred Werner’s coworker C. Schwenk. 1913 dred years later. It still can be considered imaginative abilities and how his inspira- was a good year for Alfred Werner, since a proper base for research and teaching tions came about via selective insights into he was also awarded the Nobel Prize[1] and in schools and academics. The University his developments in coordination chemistry. his coordination chemistry became broadly of Zurich is proud to once have hosted Before we start a deeper ‘analysis’ of accepted. Despite this broad acceptance, Alfred Werner and to have been the place Alfred Werner’s intuition and inspiration and even a personal visit on his return trip that provided him opportunity to lay the on the basis of accounts of his work de- from Stockholm, Alfred Werner was never foundations of coordination chemistry. posited in the form of original samples, we able to reconcile with his chief scientific Alfred Werner’s book is to a great extent would like to briefly review his life and his adversary Jørgensen (University of Copen- a personal account overviewing his and views of coordination chemistry. hagen). Not too long after Alfred Werner his research group’s achievements in the fell ill, with continuous physical and men- field. In this article we will review ex- tal decline from 1915 till his death in 1919. cerpts from his book. We do not attempt Short Survey of Alfred Alfred to be comprehensive in tracing the basis Werner’s Life Alfred Werner’s Scientific Life for today’s coordination chemistry and its extension into other areas; rather we Werner’s short but intense life[2] was 1866 Born in Mulhouse would like to go back to the roots of Al- dedicated mainly to chemistry. His devotion 1887 Enrollment as a student of chemis- fred Werner’s chemistry in a more per- to chemistry started with first inspirations try at the ETH Zürich Aspects of Chemistry at UZH from Werner to the Present Day CHIMIA 2009, 63, No. 9 543

Fig. 3. Positional isomerism in praseo and violeo salts as interpreted by Blomstrand-Jørgensen Fig. 2. Alfred Werner. and Werner.

1889 Diploma of Chemistry, ETH Zürich Blomstrand-Jørgensen concept and Alfred The anionic (Co-NO2 or Pt- 1890 PhD with Prof. Hantzsch at ETH Werner’s theory is exemplified in Fig. 3 Cl) can be replaced with neutral ligands + + Zürich with the praseo and the violeo salts. (Co-NH3 or Pt-NH3 ) without loss of pri- 1892 Habilitation ETH Zürich, unsala- Concomitant with these stereochemi- mary valency. The primary valency cor- ried Privatdozent cal views, Alfred Werner put forward a new responds to a saturation of charges in the 1892 Werner met Prof. A. Miolati concept of bonding in complexes, which complexes; in certain cases the demand 1893 Associate Professor, University of he denoted as ‘higher order compounds’. for ionic saturation cannot be satisfied, Zurich The higher order was derived from the ap- leaving charge behind, although the com- 1893 Coordination theory parently inevitable distinction between a pounds still possess some ligands bound 1895 Full Professor, University of Zurich primary (Hauptvalenz) and a secondary through primary valency. 1895 Marriage and Swiss nationality valency (Nebenvalenz). In his terminology It can be speculated that the formula- 1905 Book ‘Neuere Anschauungen auf the primary valency caused ‘inclusion’ tion of this primary valency as a binding dem Gebiete der Anorganischen complexes (‘Einlagerungsverbindungen’), category of its own had to do with Alfred Chemie’ which would in modern terms be attributed Werner’s primary experience in conduc- 1909 New chemistry building a metal– bonding mode based for- tivity measurements (initially together 1910 Discovery of the chirality of com- mally on radicals allowing formulation of a with Professor A. Miolati from Turin). plexes by coworker V. L. King covalent interaction. As an additional fea- The replacement of ionic ligands by neu- 1913 Discovery of inorganic non-carbon ture of this primary valency, Alfred Werner tral ones allows series of complexes to containing chiral complexes by co- realized that these radical derived bonds be established with different charges, but worker C. Schwenk are made in complexes from ligand spe- with a stable number of primary valen- 1913 Nobel Prize cies stable as anions in the free state. These cies. Fig. 5 demonstrates such a series and 1915 Descent into illness anions can thus be replaced by neutral li- their conductivities. 1919 Death gands without destruction of the primary Secondary valency was meant to give valency or exchange of it into a secondary rise to addition compounds (‘Anlager- one. Primary valency in complexes is thus ungsverbindung’), which in more mod- Alfred Werner’s Views of expressed and can be counted by overall ern binding terms could be described as Coordination Chemistry as charges on the complex and the number Lewis acid–base interactions. Typical Documented in Werner’s Book of anionic ligands. To illustrate this we interactions of secondary valency were would like to analyze the equations in Fig. described in Alfred Werner’s book, for Alfred Werner revolutionized the world 4, taken directly from Werner’s book (3rd instance for metal carbonyls (Fig. 6). of coordination compounds by stating a ed., p. 46). This excerpt from his book (3rd ed., p. new set of stereochemical and bonding 303) witnesses not only the book’s actu- principles.[1–3] He proved the Blomstrand- ality, but also the correct view of binding Jørgensen concept of coordination chem- of CO to a metal center to form ‘addition’ istry wrong, which restricted itself to two- compounds. It should be noted at this point dimensional ‘flat’ views of coordination that the cited discoverers of metal carbon- compounds and gave rise to a great deal yls Mond and Langer described incorrectly of conceptual inconsistency. Giving com- the ‘constitution’ of metal carbonyls. First plexes a third dimension provided correct of all in their view these were ‘flat’ mol- explanations for their inherent principles ecules closer in their representation to the of isomerism including those originating Blomstrand-Jørgensen theory,[2] and sec- from chirality. The different ways of ex- Fig. 4. Equations taken from Werner’s book, ondly in Alfred Werner’s terminology they plaining positional isomerism within the 3rd ed., p. 46. would have been ‘inclusion’ compounds. 544 CHIMIA 2009, 63, No. 9 Aspects of Chemistry at UZH from Werner to the Present Day

be replaced by Kossel’s theory of 1916, which was very similar to Lewis’ theory of 1923. Indeed the Kossel/Lewis theory brought about more unifying electronic views on valency in general and on that of complexes in particular.

Werner’s Intuition

As we said intuition is based on imagi- nation, inspiration and knowledge. We have already seen where Werner’s inspirational moments could have had their origins in Fig. 5. Conductivities for the complex series his life. We next would like to approach Werner’s intuition. Since scientific intu- [Co(NH3)6-n(NO2)n]Cl3-n (n = 0 – 3). Plot taken ition needs concepts, and we surveyed his from Werner’s book concepts concerning coordination theory, (3rd ed., p. 46). so that we would now be able to trace Wer- ner’s intuition by contemporary studies of the Werner Collection of Samples, which will be described in the form of anecdotes in Part II and III of this series.

Acknowledgements I am very grateful to my friends and colleagues from the Fachbereich Chemie of the University of Zurich, who over the years contributed to strengthen my motivation to write this article. I am especially indebted to Professor emerit. Clive Küenzle, former Vice-Rector of the University of Zurich, who gave me strong support from the Head Office of the University of Zurich to work on the historical tracks of Alfred Werner. Also I would like to acknowledge support from Professor Mary Virginia Orna, Chemical Heritage Foundation of the American Chemical Society, who often came to visit the Fachbereich Chemie and the Werner Collection Fig. 6. Excerpt of the University of Zurich, and motivated me from Werner’s book to stay on the historical tracks of Alfred Werner. (3rd ed., p. 303) Finally I would like to acknowledge the help of describing secondary Privatdozent Dr. Nathaniel Finney, Organisch- valencies in carbonyl Chemisches Institut der Universität Zürich, who compounds. revised this manuscript. Received: June 12, 2009

[1] A. Werner, ‘Ueber die Konstitution und Fig. 7. Mond/Langer descripti- Konfiguration von Verbindungen höherer – Addition compounds (Anlagerungs- Ordnung’, Vortrag, gehalten in Stockholm on of­­ ­nickel carbonyl verbindungen) are based on secondary am 11. Dezember 1913 im Anschluss an die valency, which are coordinative bound Entgegennahme des Nobelpreises, Verlag Julius – Affinity theory, corresponds to a Springer, Berlin, Germany, 1914. ‘qualitative’ quantification of binding [2] Fasciculus Extraordinarius Alfred Werner, 1866–1919, Edendum Curavit Societas Chimica strength in complexes Helvetica, Alfred Werner Commemoration Vo­ Nickel carbonyl, Ni(CO)4, thus featured in lume, Werner Celebration, IX. ICCC 1966, Verlag the Mond and Langer representation as a To conclude this overview of Werner’s Helvetica Chimica Acta, Birkhäuser Basel, cyclic organic molecule (Fig. 7). book and theory, it must first of all be Schweiz, 1967, 1–223; G. B. Kauffman, ‘Alfred Werner: Founder of Coordination Chemistry’, Within the concept of primary and sec- said that a great deal Werner’s theory has Springer Verlag, Berlin, Germany, 1966; G. B. ondary valencies, Alfred Werner applied the to be considered heuristic: when applied Kauffman, Archives de Sciences 1992, 45, 249. term affinity. Affinities presumably meant to complexes it worked well, but in great [3] P. J. Ramberg, ‘Chemical Structure, Spa­tial in this context binding strength in complex- parts it seemed somewhat diffuse. In mod- Arrangement: The Early History of Stereo­ es, which allowed qualitative modification ern terms the diffuseness came from the chemistry, 1874–1914’, Ashgate Publ. LTD, Aldershot, UK, 2003, Chap. 9; G. B. Kauffman, of these valencies. The listing below sum- fact that his picture was not electronically ‘Theories of Coordination Compounds, Werner, marizes Werner’s binding concept: based, unlike Lewis’s theory. This was the Alfred Triumph, Coordination Chemistry – A – Inclusion compounds (Einlagerungs- main criticism of P. Pfeiffer, who therefore Century of Progress’, ACS Symposium Series verbindungen) based on primary va- changed the chapter on binding theory in 565, 1994, 3–33; G. B. Kauffman, Chem. Educ. 1979, 56, 496; G. B. Kauffman, Chem. Educ. lency, describes binding of ionic units the last edition of Werner’s book. In the 1972, 49, 813; G. B. Kauffman, J. Ind. Chem. and replacement of ionic units by neu- preface to this edition P. Pfeiffer wrote Soc. 2003, 80, 601; L. H. Gade, Chemie in un- tral units leaving charges that Werner’s theoretical concept should serer Zeit 2002, 36, 168.