Werner s theory of coordination compounds

Solvates are perhaps less prevalent in compounds prepared from liquid ammonia solutions than are hydrates precipitated from aqueous systems, but large numbers of ammines are known, and their study formed the basis of Werner s theory of coordination compounds (1891-5). Frequently, however, solvolysis (ammonolysis) occurs (cf. hydrolysis). Examples are ... 

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]). 

Sidwick and Lowry gave the electronic interpretation of Werner s theory of coordination compounds. According to them p-imary valencies result from the transference of electrons, whereas secondary valencies result frem the sharing of electrons, i.e. there is a formation of electrovalent bond in primary valencies and coordinate bond in secondary valencies. They also pointed out that all ligands (neutred molecules or anions) have atoms with at least one lone pair of electrons. They donate this lone pair of electrons to the central metal ion and form coordinate... 

Discuss Werner s theory of coordination compounds and its experimental verification... 

Werner s Theory of Coordination Compounds An Overview 24-2 Ligands 24-3 Nomenclature 24-4 Isomerism... 

Inorganic coordination chemistry was a hot field of research in the second half of the nineteenth century, and all the pieces started to fall into place with the work of the Swiss chemist Alfred Werner. Werner s theory of coordination compounds explained the reactions of compounds (a) and (b) with AgN03(aq) by considering that, in aqueous solutions, these two compounds ionize in the following way ... 

Werner s Theory of Coordination Compounds An Overview—Many metal atoms or ions, particularly among the transition elements, have the ability to bond with ligands (electron-pair donors) to form a complex, a species in which there are coordinate covalent bonds between ligands and metal centers. The number of electron pairs donated to the central metal atom or ion by the ligands is the coordination number. A compound having one or more complexes as a constituent is called a coordination compound. 

Alfred Werner (working at the University of Zurich) was awarded the Nobel Prize for Chemistry in 1913 for his pioneering work that began to unravel the previous mysteries of the compounds formed between block metal ions and species such as H2O, NH3 and halide ions. A famous problem that led to Werner s theory of coordination concerns the fact that C0CI3 forms a series of complexes with NH3 ... 

We saw in Section 1.3 how Alfred Werner formulated the modern concept of coordination chemistry, which supramolecular chemistry generalises to a complete coordination chemistry . Prior to Werner s time the chain theory of coordination compounds was popular. The chain and Werner formulations of Co (NIT3) 4CI3 and Co (NH3) 3C13 are shown in Figure 3.1. While both theories predict that Co (NH3) 4C13 will exhibit one labile chloride ion per molecule, the chain theory also predicts that Co(NH3)3C13 will have one labile chloride, while Werner s theory ultimately correctly predicted that the chloride is not labile in this case. 

Werner s most important contribution, his theory of valency and the structure of coordination compounds, was first presented in 1891 to qualify for a post in the Zurich Polytechnic. He assumed that the valency of an atom, including the carbon atom, is an attractive force emanating from the centre and acting uniformly towards all parts of the surface, rather than directed valency bonds. Although he claimed that this would lead to van t Hoff s configurational formulae, it is on the basis of the latter and directed bonds that Werner s own theory of coordination compounds has been most successfully explained. 

But Kekuld s stability criterion, or to be more accurate, instability criterion failed completely in the case of many coordination compounds, especially the metal-ammines, which were classified as molecular compounds by sheer dint of necessity even though they were extremely resistant to heat and chemical reagents. For example, look at Figure 1. Although hexaamminecobalt(III) chloride contains ammonia, it neither evolves this ammonia on mild heating nor does it react with acids to form ammonium salts. Also, despite its cobalt content, addition of a base to its aqueous solution fails to precipitate hydrated cobalt(III) hydroxide. It remained for Alfred Werner to explain successfully the constitution of such compounds, but the time was not yet ripe. Before considering Werner s coordination theory, we must examine one more theory of coordination compounds, perhaps the most successful of the pre-Wemer theories, namely, the Blomstrand-J0rgensen chain theory. 

However, as the chapters in this volume illustrate, the theoretical and practical aspects of coordination chemistry in general and Werner s work in particular have significance in fields far removed from classical inorganic chemistry. Because of the importance of Werner s research on coordination compounds, they are sometimes referred to as Werner complexes, and the coordination theory is colloquially called Werner s theory. Werner s work was so complete and all-encompassing that for many years coordination chemistry was neglected because most chemists thought that all the important research had been done. It remained for chemists such as John C. Bailar, Jr., in the United States and Kai Ame Jensen and Jan-nik Bjerrum in Denmark to revive interest in the field as part of what became known as the Renaissance in inorganic chemistry. Evaluations of the Uves and works of these recently deceased chemists appear as Chapters 6-9 in this volume. 

Spectroscope developed Bunsen and Kirchhoff 1869 Mendeleev s first periodic table organizes 63 known elements 1885 Balmer formula for visible H spectrum 1894 First "inert gas" discovered 1895 X rays discovered Roentgen 1896 Radioactivity discovered Becquerel 1874 Tetrahedral carbon atom Le Bel and van t Hoff 1884 Dissociation theory of electrolytes Arrhenius 1869 Chain theory of ammonates Blomstrand 1884 Amendments to chain theory Jorgensen 1892 Werner s dream about coordination compounds... 

Even so great an admirer of Werner as Paul Pfeiffer (1875-1951),93 Werner s former student and one-time chief of staff at the University of Zurich and the man who first applied Werner s theory to crystal structures (see Section 1.1.5.4), proposed modifications of the coordination theory. He applied what he called the principle of affinity adjustment of the valencies to overcome certain shortcomings of Werner s theory.94 He considered the ionizable radicals or atoms in the outer sphere to be combined with the complex radical as a whole and not attached definitely to the central atom or to any of its associated molecules. He also applied this idea to complex organic molecular compounds. However, Pfeiffer s modifications should not be interpreted as attacks on Werner s ideas. 

In the following year, 1905, Werner published his great book on coordination chemistry, and this had a powerful influence on Lewis. Werner proposed that in coordination compounds, atoms or groups of atoms surrounded a central atom to form an electrically charged ion or a neutral compound, and the geometrical or structural theory seemed to fit very nicely with Lewis s ideas. All that was needed (and it was a big all ) was a clearer picture of the electrical nature of atoms. 

In this broad chronological survey, some of the most historically significant coordination compounds are first discussed, along with several pre-Wemer theories of their formation and constitution, followed by Werner s theory and his most important discoveries. This article concludes with a brief consideration of discoveries and developments from Werner s time through 2003. ... 

Pfeiffer s application of Werner s theory to crystals and the advent of new experimental techniques led a number of scientists in various countries to use X-ray diffraction to determine crystal structures of coordination compounds. American chemist Ralph W. G. Wyckoff(l 897-1994) chose ammonium hexachloroplatinate(IV) as a crystal that should... 

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