Ammine complexes chromium

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. 

Chromium compds, listing 3 C300—C302 chromium acetylacetone 1 A53 3 C300 chromium acetylide 1 A72 chromium (III) ammine complexes 1 A277 3C300... 

The solution of chromic salt is heated to boiling and stirred continuously while concentrated ammonia water is added slowly from a tap funnel or burette. About 40ml are required to give a slight excess of the reagent. Avoid adding too much ammonia because chromium tends to form complex ammines. 

Chromium (III) ammine Complexes. These include Triazido-triamminechromium(III),... 

Chromium (ill) ammine Complexes, These include Tfiazido-triamminechromium(III), Aquopentamminechromiuni(III) Perchlorate, Azidopentamminechromium (III) Perchlorate, Chiocopentamminechromium (III) Azide, Hexamminechromium (III) Azide, Hexammine-chromium (III) Nitrate and Hexamminechromium (III) Perchromate described in Vol I, pA277... 

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 chromium (III) ammines closely resemble the corresponding cobalt(III) complexes in many respects. For example, analogous compounds in the two series are usually isomorphous and of similar color. While the preparative methods used for cobalt (III) ammines can sometimes be employed for the preparation of the corresponding chromium (III) ammines, other methods are usually preferred. Thus a mixture of a chromium (II) salt and ethylenedia-mine absorbs atmospheric oxygen even more readily than does a mixture of a cobalt (II) salt and the base. The procedure for preparing tris(ethylenediamine)chromium(III)... 

I Care should be taken to have only a slight excess of ammonia present because of the tendency of chromium to form soluble complex ammine compounds. Vigorous boiling of the solution until only a faint odor of ammonia is perceptible will prevent this. 

Recently c/ -activation has been recognized as playing an important part in chromium(m) substitutions whenever potentially chelating co-ordinated oxoanions are present e.g. NOs , SOa, AcO, S04 ). This makes it important that the correct counterion is chosen in studies of substitution reactions of cationic complexes. For example, replacing nitrate ion by perchlorate ion makes a significant difference to the rates of acid hydrolysis of some chromium(m) ammines. ... 

Ab initio calculations have also been carried out on the photochemistry of chromium(III) ammine complexes. Both ab initio calculations and the angular overlap model show that ligand rearrangements are confined to the original plane of excitation, and that the stereomobility required to obtain the predicted isomeric product can be modeled. ... 

Kinetic studies of the loss of ammonia or of chelating amines from cobalt(m) complexes by aquation are rare. Parallel loss of ammonia and halide from chromium(m)-ammine-halide complexes is not uncommon, but ammonia is very much more reluctant than halides to depart from cobalt(ra). In fact the potential field of kinetic studies of the loss of ammonia from cobalt(m) is small, and further restricted by the propensity of cobalt(m) to oxidize co-ordinated water. The [Co(NH3)(OH2)5] + cation, on warming in IM-HCIO4 for twelve hours, gives [Co(NHa)2(OH2)4] + and cobalt(ii). The... 

Table 7 Kinetic parameters for ammonia loss from chromium(iii)-ammine complexes... 

Jorgensen, E. and B)errum, J. (1958) Kinetics of complex formation. IV. Rates of decomposition and transformation mechanisms of chromium(III) ammines in aqueous solution. Acta Chem, Scand, 12, 1047-1061. 

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. 

Thermally, ammine complexes of chromium(III) containing a coordinated ligand X (where X is CL, CNS , etc.) undergo substitution of X by H20 in aqueous solution with retention of stereochemistry ... 

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. 

Chromium in the trivalent state forms a variety of salts, the most important and the simplest being the violet salts, which liberate in aqueous solution chromium cation Cr" A green series of chromic salts, isomeric with the violet salts, liberate in aqueous solution some chromium cation, whilst part of the chromium is present as a complex ion. With weak acids, sulphurous, hydrocyanic, or thiocyanic acids, the chromic ion forms complex ions of great stability. Finally, a very large group of salts exists where chromium associated with ammonia forms the complex ion, the chromi-ammines. 

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 ... 

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. 

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