Aquo compounds, ammonia

Water and ammonia, therefore, behave similarly in the formation of substitution compounds, and there is gradation from ammino-salt through aquo-ammino- to purely aquo- or hydrated salt further, the entrance of water in place of ammonia does not alter the ionic nature of the acidic radicles outside the complex. 

Corresponding to the aquo-tetrammino-derivatives a series of compounds are known containing two molecules of ethylenediamine in place of ammonia. 

The corresponding pyridino-compound, [Cr py2(H20)(OH)3], is obtained by suspending dihydroxo-aquo-dipyridino-chromic sulphate, [Cr py2(0H)2(H20)2]2S04.12H20, in water and adding concentrated aqueous ammonia. The whole goes into solution, and then crystallises in pale violet leaflets which are insoluble in water and decompose on treatment with mineral acids.5... 

The hexammino-salts are yellow or brownish compounds, easily crystallised and fairly stable. They withstand the action of boiling water for some time, and can therefore be crystallised from aqueous solution if crystallisation be carried out quickly. Acid solutions of the salts are very stable, but alkaline and neutral solutions are decomposed on heating. The salts are more soluble than the corresponding aquo-pentammino-salts, and their solutions are brownish yellow in colour. The hydrated salts effloresce in air and become opaque and reddish brown in colour. On heating they lose ammonia, leaving eobaltic oxide and a cobaltous salt. In cold solution they give no precipitate with sodium hydroxide, ammonium hydroxide, or alkali... 

The name roseo-cobaltic salts was given to the series by Fremy, but it is due to the research of later investigators, notably Jorgensen, that the roseo-salts were shown to be derived from the hexammino-compounds by replacement of ammonia by water. The salts are clearly marked off from those of the acido-pentammino-series, the purpureo-salts, where acid radicle replaces ammonia in the complex ion. The valency of the complex in the aquo-pentammino-salts is not changed by the entrance of water in place of ammonia. 

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. 

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. 

Bratsch SB, Lagowski JL (1986) Actinide thermodynamic predictions. 3. Thermodynamics of compounds and aquo-irms of the 2+, 3+, and 4+ oxidation states and standard electrode potentials at 298.15 K. J Phys Chem 90 307-312 (1987) Predicted and expraimcaital standard electrode potentials in liquid ammonia at 25°C. J Solution Chem 16 583-601... 

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