Configuration cobalt ammines

The diol-compounds are readily decomposed by concentrated hydrochloric and hydrobromic acids, yielding a mixture of m-diaquo-tetram-mino-cobaltic and cis-diacido-tetrammino-cobaltic salts, a reaction which has proved useful in determining the configuration of stereo-isomeric cobalt-ammines. 

As in the case of the mononuclear cobalt salts, the configuration of the compounds suggests that some should exist in optically active forms. Several cobalt-ammines of the polynuclear series have been resolved into their optically active isomers. 

Let us now examine the means used by Werner to establish the configuration of cobalt ammines.S3 Hie technique of isomer counting that Werner used as a means of proving configuration... 

The technique of isomer counting used by Wemer to prove the configuration of cobalt-ammines and other complexes did not originate with him, but had been used earlier by Wilhelm Kdmer for benzene derivatives in 1874, and was also suggested by Jacobus Henricus van t Hoff in 1875. However, the technique of comparing the number and type of isomers actually prepared with the number and type theoretically predicted for different configurations probably attained its zenith with Wemer. Not only did he use this method to discredit completely the chain theory bnt also to... 

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... 

After the resolution of 1-2-chloro-ammino-diethylenediamino-cobaltie chloride many analogous resolutions of optically active compounds of octahedral symmetry were carried out, and active isomers of substances containing central cobalt, chromium, platinum, rhodium, iron atoms are known. The asymmetry is not confined to ammines alone, but is found in salts of complex type for example, potassium tri-oxalato-chromium, [Cr(Ca04)3]K3, exists in two optically active forms. These forms were separated by Werner2 by means of the base strychnine. More than forty series of compounds possessing octahedral symmetry have been proved to exist in optically active forms, so that the spatial configuration for co-ordination number six is firmly established. 

The procedure described here is based on the observation that amine monohydroxo complexes of cobalt(III), rhodium(IIl), and iridium(III) react directly with carbon dioxide to form the corresponding carbonato complexes,2 3 without effect on the configuration of the amine ligands.4 The amine monoaqua complex is allowed to react with lithium carbonate or carbon dioxide gas at room temperature at pH 8.0 for a few minutes, and the carbonato complex is isolated by adding alcohol. The procedure has been used to prepare salts of the following cations pentaammine(carbonato)-cobalt(III),2 ds-ammine(carbonato)bis(ethylenediamine)cobalt(III),5 trans-... 

Mast and Sykes (15) have recently investigated the kinetics of interconversion reactions of some binuclear cobalt(III) ammines. They have reported both chemical and kinetic evidence for the existence of the diaquo complex [(H20)(NH3)4CoNH2Co(NH3)4(H20)]+ a complex not previously prepared. Garbett and Gillard have reported similar interconversions with ethylenediamine ligands (8) and have assigned optical configurations ( ). 

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. 

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