Aquo salts

Just as ammonia groups maybe replaced by acid, so ammonia groups may be replaced by water molecules. These aquo salts, as they arc called, were represented by Jorgensen 1 as oxonium salts. For instance, dichloro-tetrammino-cobaltic chloride is transformed into aquo-dichloro-triammino-cohaltic chloride by replacement of one ammonia, molecule by one water molecule, a reaction which was represented thus ... 

Aquo-pentammino - magnesium Chloride, [Mg(NH3)5H20]Cl2. —A colourless crystalline aquo salt is described which is produced by passing ammonia gas into an alcoholic solution of magnesium chloride at ordinary temperature.4... 

When aquo-pentammino-saits lose water the acid residue enters the complex, just as in the ease of loss of ammonia from the complex. For example, aquo-pentammino-chromie chloride, [Cr(NIi3)s(II20)]Cl3, on loss of water becomes ehloro-pentammino-ehromic chloride, [Cr(NH3)5Cl]Cl2. Other aquo-salts behave similarly, and almost any acidic radicle attached to the complex as a whole may in this way be caused to enter the complex itself. 

Aquo-pentammino-chromic Bromide, [Cr(NH3)5H20]Br3, is prepared from the chloride by treating an aqueous solution of the salt with hydrobromic acid. The solution is evaporated to dryness and the residue taken up in water, filtered to remove any bromo-pentammino-chromic bromide formed, and the filtrate treated with concentrated hydrobromic acid to precipitate the aquo-salt, which is then washed with alcohol. It forms a yellow crystalline powder, easily soluble in W ater, and much more stable than the corresponding chloride. At 100° C. it loses water, and is transformed into bromo-pentammino-cliromic bromide. 

Aquo-pentammino-chromic Nitrate, [Cr(NH3)5H20](N03)3, may be formed by a method similar to that for the bromide, or it may be produced by treating cliloro-pentammino-ehromie chloride in aqueous solution with 1-4 nitric acid and allowing the mixture to stand at 0° C. The solution is filtered and treated with a further portion of nitric acid and allowed to stand at 0° C., when the aquo-salt crystallises out.2 It is a yellowish-red crystalline salt, easily soluble in water, and decomposes if heated to 100° C. 

The oxalate, [Cr(NH3)4H20.Cl]C204, separates in violet-red crystals on the addition of potassium oxalate to a solution of the chloride. It is sparingly soluble in water, and the solution gives a precipitate of calcium oxalate with calcium chloride. A freshly prepared solution of the salt in nitric acid gives no precipitate with silver nitrate. The chlorine atom in the chloro-aquo-salts is within the complex, and hence silver chloride is not at first precipitated by silver nitrate on boiling with nitric acid and silver nitrate, however, chlorine is precipitated as silver chloride. 

The bromo-aquo-salts belong to the cis-series, as on treatment with potassium thiocyanate only m-dithiocyanato-chromic thiocyanate is obtained and no fraus-salt.3... 

The following scheme, given by Pfeiffer,1 shows the relationship between aeido-aquo-salts, oxalato-salts, and diaeido-salts —... 

No aquo-salts of this series are known, and only the ammino- and pyridino-derivatives have been prepared. 

A series of compounds is know ll belonging to the diaquo-series, w here ethylenediamine replaces ammonia, the diaquo-diethylenedi-amino-cobaltic salts, [Co en2(H20)2]R3. These exist in isomeric forms, intensely red a. s-diaquo-salts and browmish-red bvms-diaquo-salts. The irans-series may be produced from the eis-series by treating it with some potassium hydroxide and nibbing the brms-hydroxo-aquo-salt, [Co en2H20(0H)]R2, produced with concentrated mineral acid. 

Diaquo - dipyridino - diammino - cobaltie cliloridc, [Co py2 XII3)2 (H20)2]C13, is one of the most stable of the aquo-salts, and requires to be heated for a considerable time before it passes into dichloro-dipyridino-diammino-cobaltic chloride, [Co py2(NII3)2Cl2]Cl. The aquo-pentammino-cobaltic salts, on treatment with ammonia, may be changed into hydroxo-pentammino-cobaltic salts thus ... 

The aquo-salts generally readily pass into the acido-ammino salts for example, aquo-pentammino-eobaltic chloride and diaquo-tetram-mino-cobaltic chloride are transformed into ehloro-pentammino-cobaltic chloride and dichloro-tetrammino-cobaltie chloride respectively on leaving concentrated aqueous solutions to stand for some time. 

The hydroxo-pentammino-salts are obtained from the aquo-pent-ammino-salts, [Co(NH3)5H20]R2, on treatment with aqueous ammonia, and they pass quickly into the aquo-salts again on treating with acid thus ... 

It is fairly soluble in water, giving a bluish-red alkaline liquid, which gives no precipitate with silver nitrate. When added to ammonium salts, ammonia is liberated and the aquo-salt formed thus ... 

The bromide, [Co(NH3)5OH]Br,.H20, is prepared from the corresponding aquo-salt in the same manner as the chloride, and separates from alcohol and water as a violet powder. The iodide, [Co(NHs)5OH]I2, is obtained from the chloride by dissolving it in aqueous ammonia and adding solid potassium iodide. The dithionate, [Co(NH3)5OH]S206. H,0, obtained from the chloride by treating it with ammonia and sodium dithionate, crystallises in short red prisms or leaflets. 

The salt is a reddish-violet crystalline substance which is slightly soluble in cold water, but easily soluble in hot water containing nitric acid, forming the aquo-salt. 

Aquo - derivatives of nitrato - pentammino - salts are known. For example, nitrato-aquo-tetrammino-cobaltic nitrate, [Co(NH3)4 (H20)(X03)](X03)2, is prepared from carbonato-tetranunino-eobaltic nitrate, [Co(XH3).1(C03)]N03,a by treating it in aqueous solution with concentrated nitric acid, when the aquo-salt is precipitated. 

They are isomeric with chloro-nitro-tetrammino-cobaltic chloride, [Co(NH3)4(N02)C1]C1.H20, and bromo - nitro - tetrammino - cobaltic bromide, [Co(NH3)4(N02)Br]Br.H20, the substances originally described by Jorgensen as aquo-salts. These salts are red, whereas all the aquo-nitro-salts are yellow in colour. Both salts are easily transformed into the isomeric nitro-halogeno-compounds on treatment with water.3... 

The salts were at first described by Jorgensen as aquo-salts, as they are formed from aeido-nitro-salts by the action of dilute aqueous ammonia but this was contradicted by Werner, who showed that they contain a hydroxo-group in the nucleus.4... 

That is, a mixture of 1-, 2-diaquo-tetrammino-cobaltic chloride and 1-, 2-diehloro-tetranimino-cobaltic chloride is formed. The aquo-salt is readily soluble in water but the diehloro-salt sparingly so. The last named forms intense blue crystals which are contaminated with small quantities of the praseo-salt, from which it may be freed by transforming it into the dithionate. The dithionate is practically insoluble, but the chloride may be regenerated from it by rubbing it with ammonium chloride. The bromide, the iodide, and the nitrate have all been prepared. 

The chloride crystallises with H20, which may be removed on heating the salt to 60° C. The other salts are anhydrous. All are intensely blue in colour, and their solutions in water are less stable than the praseo-salts. Even at 0° C. the solutions rapidly change to reddish violet, due to formation of chloro-aquo-salts. If suspended in concentrated hydrochloric acid the chloride is converted into the praseo-salt. 

The corresponding chloride, [Co(NH3)4Br2]Cl.H3G, is produced by treating the bromide with concentrated hydrochloric acid. It crystallises in green prismatic needles which are soluble in water and quickly hydrolyse in solution at ordinary temperature, with formation of the aquo-salt. 

Aquo-salts of the dichloro-series are known. These appear to exist in isomeric forms. The constitution of the salts was proved by Werner and Jorgensen.1... 

These aquo-derivatives are typical aquo-salts, and behave like the aquo-salts of the single cobalt-ammines. In aqueous solution they are further hydrated thus ... 

The acido-aquo-salts can change into diacido-salts on treatment with acid. For example, if chloro-aquo-octammino-/i-amino-dieobaltie chloride be treated with concentrated nitric acid the molecule of water is replaced by the nitrate radicle, giving chloro-nitrato-octaminino- -amino-dieobaltic nitrate,... 

The salts of the series are bright red crystalline bodies. They are soluble in water, neutral in reaction, and dilute mineral acids do not transform them into aquo-salts. The least soluble member of the series is the sulphate [(NH3)4Co (OH)2 Co(NH3)4](S04)a.2H30, which is prepared by heating hydroxo-aquo-tetrammino-cobaltic sulphate at 100° C. till it is constant in weight. The mass is extracted with water and the sparingly soluble sulphate collected and dried. The crude product so obtained is converted into the chloride and an aqueous solution of this then treated with a solution of sodium sulphate, when a crystalline precipitate of the diol-sulphate is obtained. It is collected, washed with water, alcohol, and finally with ether. It forms small red needle-shaped crystals which contain two molecules of water of hydration. 

This series of compounds, if decomposed by the halogen acids, gives quantitative yields of triammino-cobaltic salts hence three ammonia molecules are attached to each cobalt atom. The acid residues in the salts are readily ionised, and each salt may be transformed into the other by double decomposition. These compounds are not aquo-salts, and their aqueous solutions are neutral in reaction. 

This was rejected by Werner,2 as it did not agree with the properties of the substances. Thus, the salts do not yield aquo-salts on heating with dilute mineral acids, therefore the hydroxyl group cannot be directly united to cobalt as in the hydroxo-salts. The chloride of the series cannot have chlorine in the complex, otherwise the salt could not... 

The true nature of the hydroxo-compounds is further proved by the fact that the halogen salts are less soluble in acetic acid than in pure water, hence acetic acid is not a sufficiently strong acid to form aquo-salts. 

The aquo-salts are extremely easily hydrolysed, and even moistening with water causes them to decompose, with formation of the less soluble liydroxo-salts. Alcohol also causes hydrolysis of the compounds. The behaviour of the salts towards water resembles that of the diaquo-dipyridino-diammino-cobaltic salts. Thus, the bromide, HaO py2 i... 

The sulphate, [Rh(NH3)5H20]2(SQ4)3.2H20, is produced from the hydroxide on treatment with dilute sulphuric acid and precipitation with alcohol. It separates in small white oetahedra, and, unlike the other aquo-salts, is not converted into the sulphato-salt on boiling with water. It crystallises in large quadratic prisms, and at 100° C. rapidly loses water. 

Aquo -pentammino -iridium Chloroplatinate, [Ir(NH3)5H20]2 (PtCl6)3, is produced by the addition of chloroplatinic acid to any of the aquo-salts. It separates as a yellow crystalline precipitate. 

Aquo - pentammino - iridium Ferricyanide, [Ir(NH8)6H20] [Fe(CN)e], is precipitated as a reddish-brown crystalline powder on the addition of potassium ferricyanide to the aquo-pentammino-salts. All the aquo-salts yield violet-coloured solutions with chlorine, due probably to the formation of iridic compounds. 

Nitrato-pentammino-iridium Nitrate, [Ir(NH3)5N03](N03)2, is also produced by heating the corresponding aquo-salt to 100° C. It separates in microscopic quadratic plates, is soluble in water, and explodes on heating.2... 

The dihydroxo-salts show little tendency to form aquo-salts. Thus the chloride if mixed with hydrochloric acid yields hydroxo-aquo-tetrammino-platinic chloride, but the substance is so unstable that atmospheric moisture converts it quickly into the dihydroxo-chloride and hydrochloric acid.1... 

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