Coordination compounds early theories

At about the time that Claus proposed his ammonia theory, the concept of valence was being formulated and developed by a number of chemists — in particular, Kekule, Frankland, Williamson, Odling, Kolbe and Couper. During the late 19th and early 20th centuries the principal difficulty in the field of valence was its application to all types of chemical compound, and one of the main controversies involved whether or not a given element could possess more than one valence. Since coordination compounds pose a number of basic constitutional problems, it is not surprising that they became involved in the question of variable vs. constant valence. 

Photochemistry as a science is quite young we only need to go back less than one century to find its early pioneer [1], The concept of coordination compound is also relatively young it was established in 1892, when Alfred Werner conceived his theory of metal complexes [2]. Since then, the terms coordination compound and metal complex have been used as synonyms, even if in the last 30 years, coordination chemistry has extended its scope to the binding of all kinds of substrates [3,4],... 

Kettle, S. F. A. (1969). Coordination Compounds. New York Appleton, Century, Crofts. The early chapters give a good survey of the field, and the later chapters deal with details of bonding theory in coordination compounds. 

Tt is well-known that Werner determined the structure of a number of metal complexes by skillfully combining his famous coordination theory with chemical methods (30). Modern physico-chemical methods such as x-ray diffraction and infrared spectroscopy, used in the study of Werner complexes, have paralleled the development of these techniques. The results of these investigations have not only confirmed the validity of Werner s coordination theory but have also provided more detailed structural and bonding information. In early 1932, Damaschun (13) measured the Raman spectra of seven complex ions, such as [Cu(NH3)4]" and [Zn(CN)4j and these may be the first vibrational spectra ever obtained for Werner complexes. In these early days, vibrational spectra were mainly observed as Raman spectra because they were technically much easier to obtain than infrared spectra. In 1939, Wilson 35, 36) developed a new theory, the GF method," which enabled him to analyze the normal vibrations of complex molecules. This theoretical revolution, coupled with rapid developments of commercial infrared and Raman instruments after World War II, ushered in the most fruitful period in the history of vibrational studies of inorganic and coordination compounds. 

Walter Hleber (1895-1976) was a student of Rudolf Weinland, who performed early experimental work on Alfred Werner s theory of coordination compounds (Hauptvalenzen, Nebenvalenzen). Hieber received his Ph. D. in 1919 from Tubingen University on a topic concerning ferric complexes of hypophosphorous acid. He then developed metal carbonyl chemistry, mainly at Technische Hochschule Miinchen (1935-1964) he is now considered the pioneering researcher in this area of study. His name is associated with compounds like HCo(CO)4 and H2pe(CO)4 that are relevant to catalytic hydrogen-transfer reactions (hydroformylation Section 2.1.1). Nucleophilic addition to metal carbonyls, e. g., Fe(CO)5 -i-OH —> [(C0)4FeC(=0)0H] , is known as the Hieber base reaction (cf. [76]). 

As is well known, early studies of coordination compounds primarily involved thermodynamically stable and kinetically inert complexes. These studies, mainly by Werner, Blomstrand, and Jorgensen, made possible the formulation of the coordination theory by Werner and led to the discovery of the spatial structure of complexes. The resolution of optical isomers, obviously the most spectacular evidence for the octahedral configuration of certain complexes, could be achieved only by the study of inert complexes. Consequently, the study of complex equilibria at this time was of secondary Importance. 

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