Theory Of Coordination Compounds

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Alfred Werner (1866-1919). (Reproduced with permission from reference 7,frontispiece.Copyright 1966 Springer-Verlag.)

In Coordination Chemistry; Kauffman, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.

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Theories of Coordination Compounds
Alfred Werner's Triumph George B. Kauffman
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Department of Chemistry, California State University, Fresno, CA 93740

The supersession of the most successful pre-Werner theory of the structure ofcoordination compounds, the so-called BlomstrandJørgensen chain theory, by Alfred Werner's coordination theory constitutes a valuable case study in scientific method and the history of chemistry. The highlights of the Werner-Jørgensen controversy and its implications for modern theories of chemical structure are sketched in this article.

Coordination compounds are of great practical importance.Coordinating agents are used in metal-ion sequestration or removal, solvent extraction, dyeing, leather tanning, electroplating, catalysis, water softening, and other industrial processes too numerous to mention here. In fact, new practical applications for them are found almost daily. They are of tremendous importance in biochemistry. For example, vitamin B is a coordination compound of cobalt, thehemoglobin of our blood is a coordination compound of iron, the hemocyanin of invertebrate animal blood is a coordination compound of copper, and the chlorophyll of green plants is a coordination compound of magnesium. Yet, as we shall see, their primary importance for chemistry lies elsewhere.
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Theories of Coordination Compounds In most fields of science theory generally lags behind practice.In other words, sufficient experimental data must be accumulated before attempts are made to explain these experimental facts and predict new phenomena. During the first half of the 19th century discoveries of coordination compounds were few, sporadic, and often accidental, and it was not until after Gibbs and Genth's classic memoir of 1856 that chemists began to devote themselves in earnest to asystematic study of this field. We might therefore think that few theories of coordination compounds were advanced until late in the second half

This chapter reprinted with permission from Spectrum (Pretoria) © 1987 Foundation for Education, Science and Technology In Coordination Chemistry; Kauffman, G.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.

4COORDINATION CHEMISTRY

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of the 19th century, but this was not the case. In coordination chemistry the lag of theory behind practice was not a great one because of the tremendous importance of coordination compounds to the general question of chemicalbonding. In the words of Alfred Werner himself, "Of all inorganic compounds, [metal-ammines] are best suited to the solution of constitutional problems It was through the investigation of metalammines that the decisive basic principles involved in the constitutional conception of inorganic compounds could first of all be clearly recognized." Because of the importance of coordination compounds tochemical bonding, theories of their structure were advanced by some of chemistry's brightest luminaries. In 1841 the Swedish chemist Jons Jacob Berzelius proposed his conjugate theory, using terms and ideas that he borrowed from the French chemist Charles Gerhardt. According to this theory, he viewed metal-ammines as conjugated or copulated compounds consisting of ammonia and a conjugate or copula....