Cobalt ammines structure

TABLE 2.2 Chain Theory Structure Predictions for a Series of Cobalt Ammine Complexes Based on the Number of Reactive Cl-... 

In 1995, Morgan et al. synthesized a layered aluminophosphate compound by using a chiral cobaltammine complex as the template for the first time.[61] Recently, the Jilin group has synthesized a number of 2-D layered and 3-D open-framework metal phosphates by using a racemic mixture or an optically pure chiral metal complex as the template, and has systematically studied the chirality transfer from the guest chiral complex templates to the host inorganic open frameworks.1901 Table 7.15 lists some metal phosphates and oxides with open-framework structures templated by optically pure or racemic cobalt ammine complexes. 

Xanthocobalt—see Cobalt, nitropentaammine-Xenon, pentafluoro-lone electron pair structure, 50 Xenon, trifluoro-structure, 45 Xenon(IV) complexes six-coordinate compounds structure, 53 Xenon hexafluoride geometry, 37 stereochemistry, 74 X-ray diffraction cobalt ammines, 13 configuration, 16 crystal structure, 15 Xylenol orange metallochromic indicator, 557... 

Alfred Werner developed the modern picture of coordination complexes in the 20 years that followed 1893, when, as a young scientist, he proposed that the well-known cobalt ammines (ammonia complexes) have an octahedral structure as in 1.3 and 1.6. 

For example, cobalt-ammine-chloride compounds of formulae Co(NH3)xCl3 were known for x = 3,4,5 and 6, all of different colors. Cobalt was considered to be trivalent, which was taken to mean that it could only bond to three entities how could that be made compatible with the known compositions Before Werner, the dominant model was that of J0rgensen, who had proposed the chain structures shown in Fig. 2.3. These did correctly capture some of the known chemical... 

These electrons may be regarded as taking part in six a bonds between the d sp hybrid orbitals of cobalt and the sp orbital of nitrogen the remaining six electrons will form three ir bonds. The structure of the complex ammine containing two atoms of cobalt,... 

The chemistry of non-peroxo polynuclear cobalt(III) ammines is reviewed with particular emphasis on Werner s major contributions. Modern work in this area has shown that Werner s conclusions regarding the structures of these compounds are substantially correct in spite of the relatively primitive techniques he had available. There is much current interest in polynuclear cobalt(III) complexes because of their relationship to oxygen carriers and intermediates in electron transfer reactions. Modern techniques such as spectroscopy and x-ray diffraction have been used to determine the electronic and molecular structures of these compounds. 

In the first decade of the 20th century, Werner published a series of 10 papers in which he reported the results of extensive investigations on the preparations and structures of a large variety of polynuclear cobalt (III) ammine complexes 29-3J, 36-38, 40). In the last paper of this series 29), Werner reviewed the results of his investigations by summarizing the results which led to his proposed structures. 

In spite of the many modern techniques available to the chemist, the known chemistry of polynuclear cobalt (III) complexes is essentially that deduced by Werner 60 years ago. Since his work, no new polynuclear cobalt complexes have been prepared and characterized and no new reactions uncovered. Modem work in this area is being aimed at attaining a better understanding of the electronic structures inherent in polynuclear ions, which would be of value in a variety of active fields. The chemistry of polynuclear complexes is important in such new areas as synthetic oxygen carriers, electron transfer reactions, and transition metal catalysis. The fact that these new investigations are solidly based on Werner s pioneer investigations testifies to the genius with which he opened up a new area of coordination chemistry, with only the simple chemical techniques available to him. His work in the area of polynuclear cobalt(III) ammine complexes should continue to serve as a model of solid research for some time to come. 

Any detailed description of the mechanism of an octahedral substitution must also account for the stereochemical changes that accompany reaction. Werner recognized this and made use of it in his discussions of the stereochemistry of reactions of cobalt(III) complexes. The available experimental results can be explained on the basis of possible molecular rearrangements and some cautious predictions can even be made. The base hydrolysis of cobalt III)ammines appears to be unique in that it often occurs with rearrangement it also affords the few known examples of optical inversion. These results can be explained by formation of a 5-coordinated species with a trigonal bipyramidal structure. Optically active metal complexes racemize by either an intramolecular or an in-termolecular process. Substitution reactions of platinum metal complexes often occur with retention of configuration. 

Joyner [76], reviewing a series of comparable kinetic studies of four solid cobalt(III) ammine azides, discussed the factors that determine the two alternative decomposition processes that yield either product CoN or cobalt(II) complexes. He concluded that the mechanisms are "independent of the nature of the cation, the nature of the salt and properties dependent on crystal structure." From a very careful appraisal of the evidence, he concluded that the course of the reaction is determined by "the very early interplay between the CoN and cobalt(II) reactions." This conclusion emphasizes the subtlety of the factors controlling decomposition behaviour. 

Attempts at identifying the influence of structme on stability have generally been inconclusive. For example, some alkali metal permanganates with comparable stmctures show similarities of decomposition behaviour [29], while, in contrast, the decompositions of several cobalt(lll) ammine azides show little evidence of structural influences [76], Significant differences in behaviour were found for the various crystal forms of the LiK tartrate hydrates [87] and, also, for the dehydrations of the isomorphic alums [20,43], However, some reactants, for example those prepared by the dehydration of hydrated metal carboxylates [5], may be amorphous to X-rays, thus preventing recognition of any control of stability by crystal structure. 

The ammines of chromium were first obtained by E. Fremy i in 1858, and they were soon afterwards studied by P. T. Cleve, and then by J. Morland, A. Eeineoke, and S. M. Jorgensen. A. Werner showed that as in the case of the cobalt, and platinum ammines, most of the chromium ammines fitted into the system based on his co-ordination theory—-8. 49, 19. I. I. ChernyefE studied the inner structure of the chromium ammines. Extensive investigations on the chromium ammines have been made by P. Pfeiffer and his fellow-workers, and the following summary is based on his reports ... 

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