SCHWARZENBACH, GEROLD KARL

(b. Horgen, Switzerland, 15 March 1904; d. Zurich, Switzerland, 20 May 1978)

chemistry.

Schwarzenbach was born and raised in Horgen, a small town situated on Lake Zurich, nine miles from the city of Zurich, His father, Jean Schwarzenbach, managed a silk-dyeing factory founded by his mother’s father and later sold by his cousin. The second youngest of seven children (three girls and four boys), Gerold was the only one to receive an academic education. In 1928 he received his doctorate, under Professor of Analytical Chemistry William Dupré Treadwell, from the Swiss Federal Institute of Technology (ETH) in Zurich with the dissertation “Studien über die Salzbildung von Beizenfarbstoffen” (“Studies on the Salt Formation of Mordant Dyestuffs”). Instead of accepting an industrial position in the textile industry, as his family desired, he spent a year (1928–1929) working on synthetic organic problems with William Bradley and Sir Robert Robinson in Manchester and London. His work in the United Kingdom on natural plant dyes gave him his first contact with substances capable of acting as ligands (complexing agents).

In 1929 Schwarzenbach returned to Switzerland and married Martha Tobler, whom he had met in London. The couple had three children: Ursula, who became a children’s nurse; Kurt, a Ph.D. chemist and product manager for Ciba-Geigy in Basel; and Dieter, professor of crystallography at the University of Lausanne. In 1929 he became chief assistant to Paul Karrer at the University of Zurich and was in charge of the analytical chemistry laboratory course for medical students and then the analytical chemistry training for natural scientists. With his Habilitationsschrift,“Die Acidität in verschiedenen Lösungsmitteln”, he qualified in 1930 to teach at a university as an unsalaried lecturer on “the entire field of chemistry.” He spent the year 1937 to 1938 in the United States, first with Leonor Michaelis as a Rockefeller Scholar at the Rockefeller Institute for Medical Research (now Rockefeller University) in New York City and then with Linus Pauling at the California Institute of Technology in Pasadena.

Schwarzenbach’s wife died in 1940. In 1942 he married Erica Schoch, with whom he later had a daughter, Annette, who became an optometrist in Zurich and Schaffhausen. In 1942 he was appointed assistant professor of analytical chemistry at the University of Zurich. In 1947 he became full professor of analytical chemistry. In 1955 he succeeded his teacher Treadwell as full professor and director of the Laboratory for Inorganic Chemistry at the ETH, where he remained until his retirement on 1 September 1973. He died unexpectedly of heart failure on 20 May 1978.

Schwarzenbach had an international reputation as a pioneer in modern coordination chemistry, but he also made valuable contributions to inorganic, analytical, physical, and organic chemistry. He was awarded the Talanta (1963), Torbern Bergman (1967), Paul Karrer, and Paracelsus medals, the Werner (1936) and Marcel Benoist (1964) prizes, and honorary doctorates from the universities of Bern (1971) and Fribourg (1974). In 1962 he was elected a foreign member of the American Academy of Arts and Sciences.

Schwarzenbach is best known among analytical chemists for his discovery and development of the complexometric titration method whereby almost every metal can be determined in a very simple manner. A suitable indicator is added to the solution of the metal to be determined, and the solution is titrated with a standard solution of a complexing agent until the indicator changes color. This method resulted from his earlier studies, which revealed the similarity between the formation of metal coordination compounds and conventional acid-base neutralization. These physical organic studies involved modern theories of acids and bases (Brønsted-Lowry and G. N. Lewis); the electronic theories of Lewis, Sidgwick, Robinson, and Pauling; and the effects of substitution on the acidity of organic compounds. Schwarzenbach’s measurements of keto-enol equilibria with a simple flow apparatus gave values that are still cited today.

During studies of the behavior of dyestuffs over a wide pH range, he found that metal cations could exert an important influence on the equilibrium and that nitrilotriacetic (NTA) and ethylenediaminetetraacetic (EDTA) acids show a decrease in pH on addition of cations of the alkaline earth elements (those of periodic group IIA). These results opened a new field, which is associated with Schwarzenbach’s name, the study of metal complexes by potentiometric measurements and the potentiometric analytical determination of metals by use of specific metal indicators (Eriochrome Black T, for example).

In 1956 in a lecture on organic ligands Schwarzenbach sketched characteristics of coordination that adumbrated the theory of “hard” and “soft” acids and bases developed a decade later. He synthesized numerous compounds to establish the structural basis for the so-called chelate effect (the increased stability of compounds containing chelate rings compared with those that do not), and he determined many complex formation constants. These results exerted a great influence on problems in biochemistry, biology, limnology, and other fields. After his move to the ETH (1955), Schwarzenbach also studied biological chelating agents such as adenosine triphosphate (ATP), phosphoglyceric acid, and iron-complexing antibiotics. He studied protonation and deprotonation processes; salt cryoscopy; polynuclear coordination compounds of chromium(III), cobalt(III), and other transition metal cations; and metal sulfides and aromatic complexes of mercury. He called his coordination chemistry in solution “measuring complex chemistry” (messende Komplexchemie), since the identification of complexes results from the elucidation of equilibria and not from the classical preparative manner. Schwarzenbach also carried out historical studies of the development of chemical concepts such as acid-base theory and valence theory.

BIBLIOGRAPHY

I. Original Works. Schwarzenbach’s more than 190 articles appeared from 1928 to 1977. Most were published in Helvetica chimica acta. A bibliography through 1963 appears in Walter Schneider, “From the Proton to the Metal Ions: Outlines of the Early Papers of Gerold Schwarzenbach,” in W. Schneider, G. Anderegg, and R. Gut, eds., Essays in Co-ordination Chemistry (Basel, 1964), 9–23, A complete bibliography appears in the obituary by Walter Schneider in Helvetica chimica acta, 61 (1978), 1949-1961. Schwarzenbach’s books include Allgemeine und anorganische Chemie: Ein einfaches Lehrbuch auf neuzeitlicher Grundlage (Stuttgart, 1940; 4th ed., 1950); Complexometric Titrations, H. M. N. H. Irving, trans., 2nd English ed. (New York, 1969); Stability Constants of Metal-Ion Complexes, 2 vols. (London, 1957), written with Lars Gunnar Sillén.

II. Secondary Literature. In addition to the works by Walter Schneider cited above, see Gerhard Geier, “Gerold Schwarzenbach zum Gedenken,” in Chemie (Switzerland), 32 (1978), 269; and McGraw-Hill Modern Scientists and Engineers, III (New York, 1980), 86–87.

George B. Kauffman