Werner’s theory

First donor-acceptor adduct (coordination compound) NH3.BF1 prepared by J. L. Gay Lussac (A. Werner s theory, I89I-5). 

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 ... 

Since a royal order, transmitted through the Viceroy of Mexico, had decreed that Werner s theory of the formation of veins be taught to the students, the brilliant young Don Andres Manuel del Rfo was sent to Mexico to introduce the most approved mining methods which he had learned at Freiberg (13). Although del Rio had declined the professorship of chemistry, he accepted that of mineralogy, and took with him on the warship San Pedro Alcantara a quantity of equipment for the School of Mines. Soon after his arrival in Mexico City in December, 1794,... 

In 1793 a royal order decreed that Werner s theory of the formation of veins be taught at the School of Mines of Mexico recently founded by Don Fausto de Elhuyar (2). The professorship of mineralogy was therefore offered to Senor del Rio, who had previously declined that of chemistry. Early in August, 1794, he set sail from Cadiz on the warship San Pedro Alcantara, taking with him a servant and a supply of apparatus for the School of Mines. Eleven weeks later he disembarked at Vera Cruz (3). 

The trinitro-triammine cobalt has practically no conductivity.3 Werner s theory is further supported by the fact that by the introduction of a fourth molecule of ammonia into the triacido-triammine compound the solution becomes once more conducting, as one (N02) group is displaced from the co-ordination complex. The eobalt-ammino-compounds, therefore, containing fewer than three ammino-radicles, contain non-ionisable acidic radicle, and those containing more than three contain ionisable acidic radicles. The generalisation made in connection with the triammino-eompounds led, therefore, to the establishment of the constitution of other ammino-derivatives, and also to the constitution of some of the ammino-salts of divalent and tetravalent metals. 

Werner s Theory—Nomenclature—Stability of Metal-Ammines. 

The double fluorides of vanadium and other double halogen salts in most cases can be regarded as in accordance with Werner s theory of co-ordinated compounds. The vanadium has a co-ordination number six. 

Potassium-ammonium double salts have also been prepared. The first two series can be looked upon as derivatives of the co-ordinated silico-acid, H8[SiIV06] the last two series cannot be formulated in accordance with Werner s theory.1... 

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... 

Friend88 specifically criticized Werner s theory and emphasized the differences between his own latent valencies and Werner s Nebenvalenzen. He applied his new theory of valency to ammonium salts, metal ammines and halide double salts , and he proposed that for hexacoordinate central atoms a hexatomic shell forms around the metal but that all the elements or groups are joined together by latent valencies and not necessarily to the metal itself. In 1916, Friend applied his cyclic theory of complexes in detail to the structures of the chlorides of hexaamminecobalt(III), chloro-pentaamminecobalt(III) and dichlorotetraamminecobalt(III) and emphasized four basic differences between his theory and Werner s.89... 

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. 

It may be added that A. Werner s theory furnishes an interesting explanation of the apparent isomorphism of such pairs of compounds as K2SnCl4.2H20... 

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. 

According to Werner s theory (see this series, Vol. X.), the formulae of hydrogen ferro- and ferri-cyanide should be written [Fe(CN)6]H4 and [Fe(CN)6]H3 respectively, the six cyanogen groups being co-ordinated with the iron atom, and constituting the nucleus around which hover the replaceable hydrogen 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. ... 

Werner s theory abraptly broke with classical theories of valence and structure, postulating two types of valence primary or ionizable valence (Hauptvalenz) and secondary or nonionizable valence (Nebenvalenz). Every metal in a given... 

In a 1908 article Friend criticized Werner s theory, differentiated between his latent valencies and Werner s... 

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... 

Bloch, E., Alfred Werner s Theorie des Kohlenstoffatoms und die Ster chemie der karbocyklischen Verbindungen, Carl Fromme, Kaiserl. und konigl. Hof-Buchdruckerei und Hof-Verlags-Buchhandlung, Vienna Leipzig, 1903. 

While Werner s ideas of primary and secondary valence were not well received during his lifetime, shortly after his death (1920) they were confirmed by Kossel, who laid the foundation for the electronic theory of valence. Furthermore, at about the same time, Wyckoff and Dickinson both confirmed Werner s theory by x-ray diffraction studies of these types of compounds. 

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