Ammines, chromium cobalt

These hydroxo-salts are all sulphur-yellow crystalline substances. The acid residues are hydrolysable and hence outside the co-ordination complex, and the aqueous solutions, unlike the hydroxo-salts of chromium-and cobalt-ammines, are neutral to litmus, a fact which Werner suggests is due to the smaller tendency of the hydroxo-radicle attached to ruthenium to combine with hydrogen ions. This tendency is much less than in the case of the ammines of cobalt and chromium, but that it still exists is indicated by the increased solubility of these hydroxo-compounds in water acidified with mineral acids, and from such solutions aquo-nitroso-tetrammino-ruthenium salts are obtained thus ... 

Ammonia forms a great variety of addition or coordination compounds (qv), also called ammoniates, ia analogy with hydrates. Thus CaCl2 bNH and CuSO TNH are comparable to CaCl2 6H20 and CuSO 4H20, respectively, and, when regarded as coordination compounds, are called ammines and written as complexes, eg, [Cu(NH2)4]S04. The solubiHty ia water of such compounds is often quite different from the solubiHty of the parent salts. For example, silver chloride, AgQ., is almost iasoluble ia water, whereas [Ag(NH2)2]Cl is readily soluble. Thus silver chloride dissolves ia aqueous ammonia. Similar reactions take place with other water iasoluble silver and copper salts. Many ammines can be obtained ia a crystalline form, particularly those of cobalt, chromium, and platinum. 

Much less is known about photoinitiated ligand exchange reactions of coordination complexes of cobalt(III) and other de ions than is the case for chromium(III). With the exception of the cobalt(III) ammines, however, available data suggest that photochemical ligand exchange reactions of cobalt(III) and d6 systems involve the thermally equilibrated 17 g and/or 37, states of the complex as intermediates. The reasoning is completely analogous to that described earlier with respect to chromium(III) photochemistry. 

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. 

All three elements form complex ammino-derivatives. Those of osmium have been very little investigated those of iridium are analogous to the anunino-derivatives of platinum on the one hand and to the ammincs of cobalt and chromium on the other whilst the platinum derivatives resemble those of cobalt, save that the metal in the platinic derivatives is tetravalent and not trivalent as in the cobalt-ammines. 

Ammonia unites readily with iridium salts, giving rise to complex ammino-derivatives. The first compounds described appear to be ammines analogous to those of palladium and platinum, to which they were compared by Berzelius 8 and Skoblikoff.4 A further series were described by Claus 5 wliich he represented like those of ammino-rhodium salts, as they bore a marked resemblance to these. After Jorgensen had established the constitution of the ammines of rhodium, cobalt, and chromium salts, Palmaer gave similar constitution to the iridium compounds. 

Platinum forms both platinous and platinie salts, in which the metal is divalent and tetravalent respectively. Both series of salts are capable of uniting with ammonia, forming complex ammines. The co-ordination number in the platinous series is four and in the platinie series six. The latter series correspond in many respects to the chromic and cobaltic ammino-salts, but as the metal is tetravalent, the maximum number of radicles outside the complex is four instead of three. Also, the ammino-bases from which the salts are derived are much more stable than those of chromium or cobalt. 

The electrical conductivity.—E. Klein10 showed that if there is a difference between the conductivity of a mixture of salts in soln. and the mean conductivities of the separate constituents, a double salt is probably formed. The molecular conductivity of a salt, and if possible of its components at different dilutions, has been employed to determine the number of component ions in a soln. it was used, for example, by A. Werner (1893-1901) with the cobalt, chromium, platinum, and other ammines.11 In moderately cone. soln. the double salts are but little ionized, and the difference between the conductivities of eq. soln. of potassium zinc chloride, ZnCl2.2KCl, and of the sum of the constituents amounts to nearly 36 per cent., a value which is greatly in excess of that whieh would be due to the mutual influence of salts with a common ion. Tables of the molecular conductivities of salts show that with very few exceptions, at a dilution of 1024 litres and 25°, most salts have conductivities approximating those indicated in Table XIX. 

Methods for the preparation and purification of salts of the dimeric complex ions di-/i-hydroxo-bis[tetraamminechromium(III)] and di-p-hydroxo-bis [bis-(ethylenediamine)chromium(III)] and of the two corresponding cobalt(III) species are presented. The two ammine complex dimers are isolated as bromide and perchlorate salts. The two ethylenediamine complexes are isolated as dithionate, bromide, chloride, and perchlorate salts. All four dimers have been obtained by heating the corresponding cis-aquahydroxo complexes as the dithionate salts. 

As examples of series of related reactions, compensation effects have been described [53] for the thermal decompositions of [CoXj (aromatic amine)2] type complexes (7 reactions) and also for a series of cobalt (III) and chromium (III) complexes (22 compounds studied in which two compensation trends were identified). Later work [54] examined the dehydrations and deamminations of dioximine complexes (two compensation trends identified), and [Co(NCS)2(ammine)2]-type complexes (three compensation trends identified). The systems involving larger entropy changes required less energy for activation [53]. Separate compensation plots for the dehydrations and the decompositions of eleven alkali and alkaline-earth metal dithionates were described by Zsako et al. [55]. 

The color and solubilities of these chromium(III) ammines are very similar to those of the corresponding cobalt(III) complexes.5 The chlorides, bromides, nitrates, and perchlorates in the acidopentamminechromium(III) series are not very soluble in water, whereas the analogous aquopentamminechromium(III) salts are soluble. In aqueous solutions, these chromium(III) ammines are much more readily decomposed than the corresponding cobalt(III) ammines. Decomposition may be perceptible within a few minutes. The absorption spectra of aqueous solutions of some acidopentamminechromium(III) salts have been studied.6,7... 

The techniques of HTRS and DRS were used by Wendlandt and co-workers (46-49) in the investigation of reactions between chromium(III) and cobalt-(III) ammine complexes and ammonium salts (thermal matrix reactions). Such a reaction is illustrated by (46). 

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