Werner s theory of coordination

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]). 

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 ... 

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. 

Claus first postulate was vigorously attacked by Karl Weltzien (1813—1870),40 while Hugo Schiff (1834—1915)43 attacked not only Claus first postulate but also his second. All of Claus three postulates reappeared modified almost four decades later in Werner s coordination theory. Claus third postulate closely adumbrates Werner s concepts of the coordination number and of the transition series between metal ammines and metal salt hydrates. 

Werner s coordination theory25 was a watershed in the history of coordination chemistry and gave the field its name. With a few exceptions, the majority of chemists accepted Werner s views, and most 20th century contributions have been developments, extensions or confirmations of Werner s theory rather than ideas incompatible with or opposed to it. Ley s concept of inner complex salts is one of the earliest of such post-Werner developments.80... 

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. 

The concept of isomerism and isomer counts were used extensively in the development of Werner s theory. They are still important, but on a much more sophisticated level than Werner could have imagined some of the structures which he used are now known to be greatly distorted22 and others are not as simple as he believed. Geometric isomers may exist in one form or another, depending upon the solvent, temperature and other conditions, or they may change their coordination numbers. For example, it has been found that [Co(PEt3)2(NCS)2] is planar in the solid state,... 

It was the optical resolution of [Co(en)2(NH3)Cl]2+ that firmly established Werner s theory and which initiated the study of the optical activity of complex ions. The realization that some octahedral complexes are chiral evidently did not occur to Werner until several years after he published his theory of coordination. He then realized that the demonstration of this property would furnish an almost irrefutable argument in favor of his theory, and he and his students devoted several years to attempts to effect such resolution. Had he but known it, the problem could have been easily solved, for cis-[Co(en)2(N02)2]X (X = Cl, Br) crystallizes in hemihedral crystals which can be separated mechanically, just as Pasteur separated the optical isomers of sodium ammonium tartrate. 

The fact that selective binding must involve attraction or mutual affinity between host and guest. This is, in effect, a generalisation of Alfred Werner s 1893 theory of coordination chemistry, in which metal ions are coordinated by a regular polyhedron of ligands binding by dative bonds. 

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. 

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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