Blomstrand’s chain theory

Comparison of Blomstrand s Chain Theory and Werner s Coordination Theory... 

Chemie (Newer Views in the Field of Inorganic Chemistry). Levi Tansjd s article, While Waiting for Werner Chemistry in Chains, which appears in this symposium volume, briefly discusses Die Chemie der Jetztzeit and Blomstrand s chain theory. 

The principal thoughts in Christian A ilhelm Blomstrand s chain theory of so-called complex inorganic compounds are briefly outlined. This theory held sway for roughly three decades until it was superseded by Alfi-ed Werner s coordination theory. 

Blomstrand s chain theory was adopted, modified and developed by his close fiiend in Copenhagen, Sophus-Mads Jorgensen (1837-1914) (7), who brilliantly defended it until Werner in 1907 - ten years after Blomstrand s death - synthesized c/5-tetraamminedichlorocobalt(ni) chloride (cis-[CoC 20 tl2) C ) (8). Then, with the words "Nu er striden afgjort" (Now the battle is over), Jorgensen graciously conceded defeat (9). 

Whereas Kekule disposed of complex compounds by banishing them to the limbo of molecular compounds , other chemists developed highly elaborate theories to explain their constitution and properties. The most successful and widely accepted of such pre-Werner theories was the chain theory,47 advanced by Christian Wilhelm Blomstrand (1826-1897)4 and developed by Sophus Mads Jorgensen (1837—1914).46 49 50 Although Werner s ideas eventually triumphed, this did not invalidate Jorgensen s observations. On the contrary, his experiments have proven completely reliable and provided the experimental foundation not only for the Blomstrand—Jorgensen chain theory but also for Werner s coordination theory. 

Table 1 A Comparison of Blomstrand—Jorgensen s Chain Theory with Werner s Coordination Theory2...

Table 1 A Comparison of Blomstrand-Jorgensen s Chain Theory with Werner s Coordination Theory. (Ref. 2b. Reproduced by permission of Dover Publications, Inc.)...

The compound C0CI3 2en (en = NH2CH2CH2NH2) contains only one chloride ion that will be precipitated immediately upon addition of silver ion. a) Draw the structure of this compound on the basis of the Blomstrand-JQrgensen chain theory of bonding. (6) Draw the structure on the basis of Werner s coordination theory, (c) Explain how each theory accounts for there being only one ionic chloride, d) Explain why the chain theory cannot account for the stereochemistry of the compound. 

The supersession of the most successful pre-Werner theory of the structure of coordination compounds, the so-called Blomstrand-J0rgensen chain theory, by Alfred Werner s coordination theory constitutes a valuable case study in scientiffc method and the history of chemistry. The highlights of the Werner-J0rgensen controversy and its implications for modem theories of chemical structure are Wretched in this article. 

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. 

The Blomstrand-Jorgensen chain theory was the most successful of the early theories that attempted to explain the known series of cobalt ammonates. This theory combined trivalent cobalt atoms, divalent ammonia radicals, and monovalent chlorides to produce structures that accounted for some of the formulas, conductivities, and reactions of these compounds. However, when an analog of a critical compound was finally synthesized, the chain theory s prediction was wrong, and it started to lose favor. 

Table 9.1 illustrates how chain theory and Werner s coordination theory predict the number of ions afforded by dissociation by various cobalt complexes. Blomstrand s theory allowed dissociation of chlorides attached to ammonia but not of chlorides attached to cobalt. Werner s theory also included two kinds of chlorides. The first kind were attached to the cobalt (these metal-bound chlorides were believed not to dissociate) these plus the number of ammonia molecules totaled six. The other chlorides were considered less firmly bound, permitting their dissociation. 

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... 

Jdrgensen s work on amine displacement constituted the groundwork for Alfred Werner, who showed that, upon further replacement of amines with anions X-, these new substituents also exhibited properties as if bound to the metal atom. Werner concluded that ammonia molecules could not exist in the chains suggested by the Blomstrand-J0rgensen theory and proposed an alternative way of viewing metal ammine bonding. Pfeiffer in 1928 described this transforming event ... 

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