(b. Mulhouse, France, 12 December 1866; d. Zurich, Switzerland, 15 November 1919), chemistry.
Life and Work. The founder of coordination chemitry, Werner was the fourth and last child of Jean-Adam Werner, an ironworker, and his second wife. Salomé Jeanette Tesché. Although the family decided to remain in Mulhouse after Alsace was annexed to the German Empire in 1871, they continued to speak French at home and their sympathies remained entirely with France. The spirit of rebellion and resistance to authority, so much a part of Werner’s childhood, may well have contributed to the revolutionary and iconoclastic character of the theory with which his name is associated. Despite his great reverence for German science— most of his articles appeared in German journals— Werner’s political and cultural ties were to France.
His mother had been converted from Protestantism to Catholicism, and at the age of six Werner was enrolled at the Catholic École Libre des Frères (Bruderschule), where the dominant traits of his personality—a remarkable self-confidence and a stubborn independence that made it impossible for him to submit blindly to authority—became evident. The religious teachings of the brothers apparently had little effect on him, for in later life his interest in religion was minimal. From 1878 to 1885 Werner attended the École Professionelle (Höhere Gewerbeschule), a technical school where he studied chemistry. During this time he built his own laboratory in the barn behind his house.
Even at this early stage Werner was preoccupied with classification, systematization, and isomeric relationships. His earliest known scientific work, “Contribution de l’acide urique, des séries de la théobromine, caféine, et leurs derivés,” a holograph manuscript that he submitted in September 1885 to Emilio Noelting, director of the Mulhouse Chemie-Schule, was banal in style and unsound in its chemical thinking; but its broad scope and daring attempts at systematization foreshadowed the intellectual heights that Werner attained only a few years later. During 1885-1886 Werner served his year of compulsory military duty in the German army at Karlsruhe, where he audited courses in organic chemistry at the Technische Hochschule. He then entered the Polytechnikum in Zurich, where he studied under Arthur Hantzsch, Georg Lunge, Heinrich Goldschmidt, and Emil Constam.
Werner was a typical nonquantitative genius. At the Polytechnikum he failed his courses in mathematics, and throughout his career his contributions were essentially of a qualitative nature; even his celebrated conductivity studies with Arturo Miolati were only semiquantitative. His failure in descriptive geometry, however, is surprising inasmuch as his coordination theory represents an inspired and ingenious application of geometry to chemistry.
On 3 August 1889 Werner was awarded a degree in technical chemistry. During 1889 and 1890 he served as an unsalaried assistant in Lunge’s chemical-technical laboratory while carrying out research under Hantzsch for which he received the doctorate on 13 October 1890.
In three short but eventful years (1890-1893) Werner produced his three most important theoretical papers. His doctoral dissertation, “Über räumliche Anordnung der Atome in stickstoffhaltigen Molekülen,” was his first publication and remains his most popular and important work in organic chemistry. By extending the Le Bel and van’t Hoff concept of the tetrahedral carbon atom (1874) to the nitrogen atom, Werner and Hantzsch simultaneously explained a great number of puzzling cases of geometrically isomeric trivalent nitrogen derivatives (oximes, azo compounds, hydroxamic acids) and for the first time placed the stereochemistry of nitrogen on a firm theoretical basis. Despite attacks by Victor Meyer, Karl von Auwers, Eugen Bamberger, and others that extended several decades into the twentieth century, the Werner-Hantzsch theory has withstood the test of time. Today, with only slight modification, it takes its rightful place beside the Le Bel-van’t Hoff concept of the tetrahedral carbon atom as one of the cornerstones of stereochemistry.
Werner spent the next two years working on his Habilitationsschrift, “Beiträge zur Theorie der Affinität und Valenz,” in which he chose to attack the supreme patriarch of structural organic chemistry, August Kekulé. In this work Werner attempted to replace Kekulé’s concept of rigidly directed valences with his own more flexible approach, in which he viewed affinity as a variously divisible, attractive force emanating from the center of an atom and acting equally in all directions. By the use of this new concept and without assuming directed valences, Werner was able to derive the accepted van’t Hoff configurational formulas. Although this important paper contains the seeds that later flowered in the primary valence (Hauptvalenz) and secondary valence (Nebenvalenz) of the coordination theory, it deals exclusively with organic compounds. Unfortunately, it was published in a rather obscure journal of limited circulation, where it elicited little notice until brought to the attention of the scientific world in 1904 by a discussion of its concept in Werner’s first textbook.
During the winter semester of 1891-1892 Werner worked on thermochemical problems with Marcellin Berthelot at the Collége de France. Except for the publication of an admittedly minor work on a basic nitrate of calcium and the incorporation of thermochemical data into Werner’s later lecture notes, this Wanderjabar had little effect on him. The acceptance of Werner’s Habilitationsschritt by the Swiss authorities early in 1892 permitted him to return to Zurich as a Privatdozent at the Polytechnikum. He did not remain there long, for in the fall of 1893 he became associate professor as successor to Viktor Merz at the University of Zurich, where he remained for a quarter-century. In 1894 Werner married Emma Wilhel-mine Giesker, a resident of Zurich, and became a Swiss citizen. The following year he was promoted to full professor. His appointment at the University of Zurich originally came about largely because of the almost overnight fame that he had received as a result of the publication of his most important theoretical paper, “Beitrag zur Konstitution anorganischer Verbindungen” ( 1893), in which he had proposed the basic postulates of his epochal and controversial coordination theory.
The circumstances surrounding the creation of the coordination theory provide a classic example of the “flash of genius” that ranks with Kekulé’s dreams of the self-linking of carbon atoms (1858) and of the benzene ring (1865). At the time (late 1892 or early 1893) Werner was a comparatively unknown twenty-six-year-old Privatdozent whose primary interest was organic chemistry and whose knowledge of inorganic chemistry was extremely limited. Yet one morning he awoke at two with the solution to the riddle of “molecular compounds,” which had come to him like a flash of lightning. He arose from his bed and wrote so quickly and steadily that by five that afternoon he had finished his most important paper
For the next decade Warnar’s attention was divided between organic and inorganic chemistry. He had originally been called to the University of Zurich to teach organic chemistry, and it was not until the winter semester of 1902-1903 that he was finally assigned the main lecture course in inorganic chemistry, which he continued to teach along with organic chemistry throughout his career. Although he became increasingly preoccupied with coordination chemistry, more than one-quarter of his publications deal with such organic topics as oximes; hydroxamic and hydroximic acids : phenanthrenes; carboxonium and carbothionium salts; hydroxylamines; azo, azoxy, hydrazo, and nitro compounds; dyestuffs; and the Walden inversion.
Nevertheless, Werner’s fame is securely grounded in inorganic chemistry. He began with a study of metal-ammines, hydrates, and double salts; but his ideas soon encompassed almost the whole of systematic inorganic chemistry and even found application in organic chemsitry. He was the first to show that stereochemistry is a general phenomenon and is not limited to carbon compounds, and his views of valence and chemical bonding stimulated subsequent research on these fundamental topics.
The coordination theory, with its concepts of coordination number, primary and secondary valence, addition and intercalation compounds, and octahedral, square planar, and tetrahedral configurations, not only provided a logical explanation for known “molecular compounds” but also predicted series of unknown compounds, the eventual discovery of which lent further weight to Werner’s controversial ideas. Werner recognized and named many types of inorganic isomerism: coordination, polymerization, ionization, hydrate, salt, coordination position, and valence isomerism. He also postulated explanations for polynuclear complexes, hydrated metal ions, hydrolysis, and acids and bases.
The average chemist probably has become familiar with Werner’s views more through his books than through his journal articles. His first, Lehrbuch der Stereochemie (1904), never achieved the popularity of his second, Neuere Anschauungen auf dem Gebiete der anorganischen Chemie (1905), which went through five editions. As Werner’s fame grew and the value of his views became recognized, he received a number of offers from Continental universities, all of which he declined. Honorary memberships and degrees were extended by many European and American universities and scientific societies. In 1913 he became the first Swiss to be awarded the Nobel Prize in chemistry, “in recognition of his work on the linkage of atoms in molecules, by which he has thrown fresh light on old problems and opened new fields of research, particularly in inorganic chemistry.” Soon afterward he began to show the signs of a chronic degenerative disease (arteriosclerosis of the brain, aggravated by excessive drinking) that progressively destroyed his physical health and mental faculties. On 15 October 1919 he was forced to resign from his laboratory and teaching duties. Exactly one month later he died after prolonged suffering.
Today, when the practical and theoretical significance of coordination compounds is unquestioned, it is clear that the foundations of modern structural inorganic chemistry were erected by Werner, who has justly been called the inorganic Kekulé
Coordination Theory. Although Werner was awarded the Nobel Prize in 1913 specifically for his monumental work on coordination compounds, the implications and applications of his research extend far beyond the confines of inorganic chemistry. In fact, they have been of inestimable value in biochemistry and in analytical, organic, and physical chemistry, as well as in such related sciences as mineralogy and crystallography. Even before Werner began his extensive series of experimental researches on “molecular compounds,” an almost unprecedented tour de force requiring a quarter of a century, he was vitally concerned with one of the most basic problems of chemistry—the nature of affinity and valence. “Molecular compounds” provided him with a challenging and exciting means to explore this question.
It may come as a surprise that the Kekulé valence theory, so flexible and fruitful in organic chemistry, proved to be a virtual straitjacket when applied to inorganic chemistry. Yet, by his own admission, Kekul’s concept of constant valence proved “embarrassing to the chemist.” Instead of abandoning this obviously untenable belief, however, he compounded the error by invoking a still more unsatisfactory concept, that of “molecular compounds,” in order to maintain it.
An example or two will suffice to illustrate Kekulé’s concept of “molecular compounds.” Since he regarded the valences of nitrogen and phosphorus as invariably three, Kekulé was forced to consider ammonium chloride and phosphorus pentachloride as “molecular compounds” with the formulas NH3 . HC1 and PC13 . C12, respectively. At most, Kekylé’s artificial division of compounds into “molecular” and “valence” compounds on the basis of their amenability of nonamenability to the doctrine of constant valence had some limited value as a formal classification, but it in no way explained the nature or operation of the forces involved in the formation of “molecular compounds” by the combination of “valence compounds.”
Whereas Kekulé disposed of metal-ammines by banishing them to the limbo of “molecular compounds,” other chemists developed highly elaborate theories in order to explain the constitution and properties of these intriguing substances. Probably the most successful and widely accepted of such theories was the one proposed in 1869 by Christian Wilhelm Blomstrand, professor of chemistry at the University of Lund. This “chain theory” was subsequently modified during the 1880’s and 1890’s by the chemist destined to become Werner’s principal scientific adversary, Sophus Mads Jørgensen, professor of chemistry at the University of Copenhagen.
Under the predominant influence of organic chemistry during the latter half of the nineteenth century, Blomstrand suggested that ammonia molecules could link together as — NH3 — chains in a manner analogous to — CH2 — chains in hydrocarbons. Provision was also made for the observed differences in reactivities of various atoms and groups in metal-ammines. For example, halogen atoms that could not be precipitated immediately by silver nitrate were regarded as bonded directly to the metal atom, while those that could be precipitated were considered to be bonded through the ammonia chains. Despite the theory’s admitted limitations, a considerable amount of empirical data could be correlated by its use.
In his revolutionary theory, which marked an abrupt break with the classical theories of valence and structure, Werner postulated two types of valance—primary or ionizable (Hauptvalenz) and secondary or nonionzable (Nebenvalenz). According to the theory, every metal in a particular oxidation state (primary valence) has a definite coordination number—that is, a fixed number of secondary valences that must be satisfied. Whereas primary valences can be satisfied only by anions, secondary valences can be satisfied not only by
|Class of Compound|
|↓ — NH3||↓ — NH3|
|↓ — NH3||↓ — NH3|
|↓ — NH3||↓ — NH3|
|↓ — NH3|
|↓ — NH3|
|Unaccountable||–||Unknown for Cobalt||(3)|
|↓ — NH3|
anions but also by neutral molecules such as ammonia. water, organic amines, sulfides, and phosphines. These secondary valences are directed in space around the central metal ion (octahedral for coordination number 6, square planar or tetrahedral for coordination number 4); and the aggregate forms a “complex,” which should exist as a discrete unit in solution.
The acknowledged test of a scientific theory is its ability to explain known facts and to predict new once. In examining the success of Werner’s coordination theory in meeting these criteria. we shall consider two aspects of the metal-ammines: constitution (how the constituent atoms and groups are bonded) and configuration (the spatial arrangement of these atoms and groups). Although we shall confine ourselves primarily to compounds of coordination number 6 [cobalt (III)], we should bear in mind that Werner used similar arguments to prove the constitution and configuration for compounds of coordination number 4.
Werner’s first published experimental work in support of his coordination theory was a study of conductivities, carried out during 1893-1896 in collaboration with Arturo Miolati. According to the new theory, the charge of a complex ion should be equal to the algebraic sum of the charges of the central metal ion and of the coordinated groups. Consequently, as neutral molecules of ammonia (A) in a metal-ammine (MA6) are successively replaced by anions (B), the number of ions in the resulting compounds should progressively decrease until a nonelectrolyte is formed and then should increase as the complex becomes anionic.
Friedrich Kohlrausch’s principle of the additivity of equivalent conductivities of salts (1879) provided
Werner and Miolati with a convenient method for determining the number of ions in various complexes. After having established the ranges of conductivities to be expected for salts of various types, they were able to demonstrate the complete agreement in magnitude, variation, and pattern between their experimentally measured conductivities (Figure 1) and those predicted according to the coordination theory. Their results were also concordant with the number of precipitable halogen atoms. The constitutions and predicted numbers of ions according to the two theories are contrasted in Table 1.
For compounds of the first three classes, the electrolytic character predicted by the two theories is in complete agreement, and conductivity data do not permit a choice between the two. For triammines, however, the ionic character differs radically according to the two theories; and the conductivities of these compounds became an important and bitterly contested issue. For some nonelectrolytes, unfortunately, Werner and Miolati’s conductivity values were not always zero because of aquation reactions:
[Co(NH3)3Cl3]0 + H2O ⇄ [Co(NH3)3(H2O)Cl2]++Cl-.
Jøgensen immediately seized upon such “discrepancies” in an attempt to discredit their results. But in its explanation of anionic complexes and its demonstration of the existence of a continuous transition series (Übergangsreihe) between metalammines (MA6) and double salts (MB6), the Werner theory succeeded in an area in which the Blomstrand-Jørgensen theory could not pretend to compete.
The technique of “isomer counting” as a means of proving configuration admittedly did not originate with Werner. The idea of an octahedral configuration and its geometric consequences with respect to the number of isomers expected had been considered as early as 1875 by van’t Hoff, and the general method probably is most familiar through Wilhelm Körner’s work of 1874 on disubstituted and trisubstituted benzene derivatives. Yet the technique of comparing the number and type of isomers actually prepared with the number and type theoretically predicted for various configurations probably reached the height of its development with Werner’s work. By this method he was able not only to discredit completely the rival Blostrand-Jørgensen chain theory but also to demonstrate unequivocally that trivalent cobalt possesses an octahedral configuration rather than another possible symmetrical arrangement, such as hexagonal planar or trigonal prismatic. The method is summarized in Figure 2 and Table II.
In most cases the number and type of isomers prepared corresponded to the expectations for the octahedral arrangement, but there were a few exceptions; and Werner required more than twenty
|TABLE II. Predicted Number of Isomers|
|Compound Type||Octahedral||Hexagonal Planar||Trigonal Prismatic*|
|*Coordination compounds with this configurations have recently been synthesized.|
|MA4B2||Two (1,2; 1,6)||Three (1,2; 1,3; 1,4)||Three (1,2; 1,3; 1,4)|
|MA3B3||Two (1,2,3; 1,2,6)||Three (1,2,3; 1,2,4; 1,3,5)||Three (1,2,3; 1,2,5; 1,2,6)|
|Two Optical Isomers||One||Two Geometrical Isomers|
years to accumulate a definitive proof for his structural ideas. For example, the best known case of geometrical (cis-trans) isomerism was observed (by Jørgensen) not among simple tetrammines MA4B2 but among salts , in which the four ammonia molecules have been replaced by two molecules of the bidentate (chelate) organic base, ethylenediamine (en); that is, among the so-called praseo (green) and violeo (violet) series of formula CoCl3 . 2en. Jørgenson regarded the difference in color as due to structural isomerism connected with the linking of the two ethylenediamine molecules, whereas Werner regarded the compounds as stereoisomers, compounds composed of the same atoms and bonds but differing in the orientation of these atoms and bonds in space (Figure 3).
If this type of isomerism were merely a geometrical consequence of the octahedral structure, as Werner maintained, it should also be observed among simple tetrammines MA4B2, which do not contain ethylenediamine. Yet for compounds [Co(NH3)4Cl2] X, only one series (praseo) was known. Jørgensen, a confirmed empiricist, quite correctly criticized Werner’s theory on the ground that it implied the existence of unknown compounds. It was not until 1907 that Werner succeeded in synthesizing the unstable, highly crucial violeo tetrammines, cis-[Co(NH3)4Cl2] X, which were a necessary consequence of his theory but not of Jørgensen’,s (Figure 4). His Danish opponent immediately conceded defeat.
Even though the discovery of the long-sought violeo salts convinced Jørgensen that his own views could not be correct, Werner’s success in preparing two-and only two-isomers for compounds of types MA4B2 and MA3B3 was not sufficient for conclusive proof of his octahedral configuration. Despite such “negative” evidence, it could still be argued logically that failure to isolate a third isomer did not necessarily prove its non-existence.
A more “positive” type of proof was necessary.
As early as 1899, Werner recognized that the resolution into optical isomers of certain types of coordination compounds containing chelate groups, which can span only cis positions, could provide the “postitive” proof that he needed. After many unsuccessful attempts, in 1911 he succeeded. His resolution, with his American student Victor King (1886-1958), of cis-chloroamminebis(ethylenedieamine)cobalt(III) salts by means of the resolving agent silver d-α-bromocamphor-π-sulfonate was sufficient to prove conclusively the octahedral configuration for cobalt(III) (Figure 5). Yet because of the prevalent view that optical activity was almost always connected with carbon atoms, a number of Werner’s contemporaries argued that the optical activity of these and the many other mononuclear and polynuclear coordination compounds subsequently resolved by him was somehow due to the organic chelate groups present, even though these symmetrical ligands were all optically inactive. Any vestige of doubt was finally dispelled by Werner’s resolution in 1914 of completely carbon-free coordination compounds—the tris[tetrammine-μ-dihy-droxocobalt (III)] cobalt(III) salts.
These Salts are compounds of the type, in which is the inorganic bidentate ligand
At the beginning of his career Werner had destroyed the monopoly of the carbon atom on geometrical isomerism. In his doctoral dissertation he had explained the isomerism of oximes as due to the tetrahedral configuration of the nitrogen atom. Now, at the peak of his career, he had likewise forced the tetrahedron to relinquish its claim to a monopoly on optical isomerism. One of the major goals of his lifework, the demonstration that stereochemistry is a general phenomenon not limited to carbon compounds and that no fundamental difference exists between organic and inorganic compounds, had been attained.
Finally, we must note that the validity of Werner’s
structural views was amply confirmed by X-ray diffraction studies. Yet, despite the advent of more direct modern techniques his classical configurational determinations by simple indirect methods remain a monument to his intuitive vision, experimental skill, and inflexible tenacity.
I. Original Works Werner’s writings include “Über räumliche Anordnung der Atome in stickstoffhaltigen Molekülen,” in Berichte der Deutschen chemischen Gesellschaft, 23 (1890), 11–30, English trans, in G. B. Kauffman, “Foundation of Nitrogen Stereochemistry: Alfred Werner’s Inaugural Dissertation,” in Jorunal of Chemical Education, 43 (1966), 155 - 165; “Beiträge zur Theorie der Affinität und Valenz,” in Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich, 36 (1891). 129–169, discussed in G. B. Kauffman, “Alfred Werner’s Habilitationsschrift,” in Chymia. 12 (1967), 183–187, English trans. in G. B. Kauffman. “Contributions to the Theory of Affinity and Valence,” ibid., 189–216; “Sur un nitrate basique de calcium,” in Annales de chimie et de physique, 27 (1892). 6th ser., 570–574, also in Comptes rendus…de I’Académie des sciences, 115 (1892), 169–171; “BEitrag zur Konstitution anorganischer Verbindungen,” in zeitschrifit für anorganische Chemie, 3 (1893), 267–330. repr. as Ostwald’s Klassiker der Exakten Wissenschaften no. 212 (Leipzig, 1924), English trans. in G. B. Kauffman, Classics in Coordination Chemistry, Part I. The selected Papers of Alfred Werner (New York, 1968). 5–88: “Beiträge zur Konstitution anorganischer Verbindungen. I.” in Zeitschrift für physikalische Chemie, 12 (1893), 35–55. “Beiträge…II,” ibid.,14 (1894), 506–521, and “Beiträge…III,” ibid.,21 (1896), 225–238–Italian trans. on Gazzetta chimica italiana, 2nd ser., 23 (1893), 140–165, 24 (1894), 408–427, and 27 (1896), 299–316, and English trans, of the first two papers in G. B. Kauffman, Classics in Coordination Chemistry, Part I (New York, 1968), 89–139; “Beitag zur Konstitution anorganischer Verbindungen. XVII, Über Oxalatodiäthy lendiaminkobaltisalze (Coc2O4en2)x,” in Zeitschrift für anorganische Chemie,, 21 (1899), 145– 158; Lehrbuch der Stereochemid (Jena, 1904)– Werner’s views on structural organic chemistry may also be found in an extremely rare monograph by E. Bloch, Alfred Werners Theorie des Kohlenstoffatoms und die Stereochemie der karbocyklischen Verbindungen (Vienna– Leipzig, 1903); Neuer Anschauungen auf dem Gebiete der anorganischen Chemie (Brunswick. 1905. 1909. 1913. 1920, 1923), 2nd ed. trans, into English by E. P. Hedley as New Ideas on Inorganic Chemistry (London, 1911); “Uber 1.2-Dichloro-tetrammin-kobaltisalze (Ammoniakvioleosalze),” in Berichte der Deutschen chemischen Gesellschaft, 40 (1907), 4817-4825. English trans, in G. B. Kauffman, Classics in Coordination Chemistry. Part I (New York, 1968), 141–154; “Zur Kenntnis des asymmetrischen Kobaltatoms. I” in Berichte der Deutschen chemischen Gesekkschaft, 44 (1911), 1887-1898, English trans. in G. B. Kauffman, Classics in Coordination Chemistry, Part I (New York, 1968), 155–173; “Zur Kenntnis des asymmetrischen Kobaltatoms. XII. Über optische AktivitÄt bei kohlenstofffreien Verbindunger,” in BErichte der Deutschen chemischen Gesellschaft, 47 (1914). 3087-3094, English trans. in G. B. Kauffman, Classics in Coordination Chemistry, Part I (New York, 1968), 175–184; and “Über die Konstitution und Konfiguration von Verbiundungen höherer Ordnung,” in Les prix Nobel en 1913 (Stockholm, 1914), trans. into English as “On the Constitution and Configuration of Compounds of Higher Order,” in Nobel Lectures in Chemistry, 1901–121 (Amsterdam, 1966), 256–269.
II. Secondary Literature. A full-length biography by G. B. Kauffman, Alfred Werner–Founder of Coordination Chemistry (Berlin–Heidelberg–New York, 1966), deals primarily with Werner’s life and career but also includes brief discussions of his work. G. B. Kauffman, Classics in Coordination Chemistry, Part I. The Selected Papers of Alfred Werner (New York, 1968), presents English translations of Werner’s six moist important papers together with critical commentary and biographical details. For other papers on various aspects of Werner and his work by G. B. Kauffman, see Journal of Chemical Education, 36 (1959), 521–527, and 43 (1966), 155–165, 677–679; Chemistry, 39 (1966), no 12, 14–18: Education in Chemistry, 4 (1967), 11–18: Chymia, 12 (1967), 183–187, 189–216, 217–219, 221–232; Naturwissenschaften, 54 (1967), 573–576; and Werner centennial, Advances in Chemistry series, no. 62 (Washington, D.C., 1967), 41–69. Articles. mostly obituaries, by others include P. Karrer. in Helvetica chimica acta, 3 (1920), 196–224, with bibliography of Werner’s publications; G. T. Morgan, in Journal of the Chemical Society (London), 177 (1920), 1639– 1648; P. Pfeiffer, in Zeitschrift für angewandte Chemie und Zentralblatt für technische Chemie, 33 (1920), 37–39; and in Journal of Chemical Education, 5 (1928), 1090-1098; and J. Lifschitz, in Zeitschrift für Elektrochemie und angewandte physikalische Chemie,26 (1920), 514–529.
The figures and tables in this article are reprinted, by permission, from G. B. Kauffman, “Alfred Werner’s Coordination Theory–A Brief Historical Introduction,” in Education in Chemistry,4 (1967), 11–18.
George B. Kauffman
FRENCH-BORN SWISS CHEMIST
Alfred Werner, the founder of coordination chemistry , was born on December 12, 1866, in Mulhouse, Alsace, France (in 1870 annexed to Germany). He was the fourth and last child of Jean-Adam Werner, a foundry worker and locksmith, and his second wife, Salomé Jeanette Tesché, the dominant figure in the Werner household and a member of the wealthy Tesché family. Although most of Werner's articles were published in the German language and in German journals, his cultural and political sympathies remained with France. The spirit of rebellion and resistance to authority that characterized his childhood and adolescence may have contributed to the development of his revolutionary coordination theory.
Werner attended the École Libre des Frères (1872–1878), and then the École Professionelle (1878–1885), a technical school where he studied chemistry. During his compulsory year of military service in the German army (1885–1886), he audited chemistry lectures at the Technische Hochschule (Technical University) in Karlsruhe. He then attended the Eidgenössisches Polytechnikum, now the Eidgenössische Technische Hochschule (Federal Polytechnic University), in Zurich, Switzerland, from which he received a degree in technical chemistry in 1889. He received his Ph.D. from the University of Zurich in 1890.
Between 1890 and 1893, Werner produced the three most important theoretical papers of his career. His doctoral dissertation (1890, cowritten with his teacher Arthur Hantzsch), a true classic of science writing on the topic of stereochemistry, extended Joseph Achille Le Bel and Jacobus Henricus van't Hoff's concept of the tetrahedral carbon compound (1874) to the nitrogen compound. It explained many puzzling paradoxes of geometrically isomeric, trivalent nitrogen compounds and placed nitrogen compound stereochemistry on a firm theoretical basis.
Werner's second theoretical paper (1891)—his Habilitationsschrift (an original article that was a requirement for teaching at a university)—took a stand against August Kekulé, the supreme architect of structural organic chemistry: It replaced Kekulé's focus on rigidly directed valences with a more flexible theory that viewed affinity as a somewhat cloudlike, attractive force emanating from the center of an atom and acting equally in all directions. During the winter of 1891–1892 Werner worked on thermochemical studies at the Collège de France in Paris with Marcellin Berthelot, but then returned to Zurich to become a privatdocent (unsalaried lecturer) at the Polytechnikum.
In 1893, at age twenty-six, Werner was appointed associate professor at the University of Zurich, largely owing to the almost overnight fame that resulted from his third article—the one that set forth his revolutionary, controversial coordination theory (which had occurred to him in a dream). Although his knowledge of inorganic chemistry was limited, he awoke at 2 a.m. with the solution of a long-standing puzzle centered on what were then called "molecular compounds." An enthralling lecturer and gifted researcher, he was promoted to full professor in 1895.
Werner discarded Kekulé's distinction between "valence" compounds, which are eminently explainable using classical valence theory, and "molecular compounds," which are not. Werner proposed a new approach in which the configurations of some compounds—metal -ammines (now sometimes called "Werner complexes"), double salts, and metal salt hydrates—were logical consequences of their coordination numbers (a new concept) and two types of valence, primary and secondary. For compounds having coordination number six he postulated an octahedral configuration; for those having coordination number four he proposed a square planar or tetrahedral configuration.
Werner's "ionogenic and nonionogenic" bonding concepts predated the currently used models of electrostatic and covalent bonding by a full generation. His ideas encompassed almost the entire field of inorganic chemistry and even found application in organic chemistry, analytical chemistry, and physical chemistry, as well as in biochemistry, geochemistry, and mineralogy. He was one of the first scientists to recognize that stereochemistry was not limited to organic chemistry, but is a general phenomenon. His coordination theory exercised an influence over inorganic chemistry comparable to that of the ideas of Kekulé, Archibald Scott Couper, Le Bel, and van't Hoff over organic chemistry.
Although today it is known that electronic configuration is the under-lying basis for chemical periodicity and the periodic system, Werner (in 1905), relying only on intuition, his vast knowledge of chemistry, and his recognition of analogies among elements, devised a "long form" of the Periodic Table, in which the lanthanide elements (inner transition elements or "rare earths" having atomic numbers 58 through 71), occupied a separate place in the table—a characteristic of all modern tables.
In 1913 Werner became the first Swiss chemist to win the Nobel Prize in chemistry, the prize given "in recognition of his work on the linkage of atoms in molecules, by which he has thrown fresh light on old problems and opened new fields of research, particularly in inorganic chemistry." Shortly thereafter, his health was declining. He died in a Zurich psychiatric hospital, on November 15, 1919. He was not only the founder of modern inorganic stereochemistry, but also one of the most brilliantly innovative chemists of all time.
see also Coordination Compounds.
George B. Kauffman
Berl, E. (1942). "Some Personal Recollections of Alfred Werner." Journal of Chemical Education 19: 153–154.
Kauffman, George B. (1959). "Sophus Mads Jørgensen (1837–1914): A Chapter in Coordination Chemistry History." Journal of Chemical Education 36(10): 521–527.
Kauffman, George B. (1966). Alfred Werner: Founder of Coordination Chemistry. New York: Springer-Verlag.
Kauffman, George B. (1966). "Foundation of Nitrogen Stereochemistry." Journal of Chemical Education 43(3): 155–165.
Kauffman, George B. (1968). Classics in Coordination Chemistry, Part 1: The Selected Papers of Alfred Werner. New York: Dover Publications.
Morgan, G. T. (1920). "Alfred Werner." Journal of the Chemical Society (London) 117: 1,639–1,648.
Pfeiffer, Paul (1928). "Alfred Werner." Journal of Chemical Education 5: 1,090–1,098; reprinted in Great Chemists, ed. Eduard Farber. New York: Interscience Publishers (1961), pp. 1,233–1,243.
Read, John (1947). Humour and Humanism in Chemistry. London: G. Bell, pp. 262–284.