Hydrates ammines

Reversible decompositions complex salts hydrates, ammines etc. Alkaline earth carbonates. 

A second difference between ammines and hydrates, again arising from the small dipole moment of the ammonia molecule, is that strong bonds cannot be formed between these molecules they are therefore found in ammines only in a co-ordinating and never in a structural capacity. For this reason the ammine counterparts of hydrates with an odd number of water molecules do not exist, and it is interesting to note, as an example of this point, that cupric sulphate forms only the hydrated ammine Cu(NH3)4S04. H20 and not the compound Cu(NH3)4S04. NH3. 

Chemical analysis and i.r. spectra of the hydrolysis products of the ammine adducts of GaF3,3NHa and InF3,3NH3 show that they are ammonium di-hydroxotrifluoro-gallate and -indate, respectively, and not hydrated ammines of the corresponding fluorides. ... 

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. 

Solvates are perhaps less prevalent in compounds prepared from liquid ammonia solutions than are hydrates precipitated from aqueous systems, but large numbers of ammines are known, and their study formed the basis of Werner s theory of coordination compounds (1891-5). Frequently, however, solvolysis (ammonolysis) occurs (cf. hydrolysis). Examples are ... 

Uptake measurements were made [16] at several oxide/solution ratios, reported as surface loading (SL) or m2 oxide surface/liter of solution, as PdCl, 2 concentration was increased and pH was held constant at the optimal value (Figure 6.10a). Each SL indeed indicated a plateau near the steric value [16], For Pt and Pd ammine cations, the maximum surface density over many oxides appears to be a close-packed layer, which retains two hydration sheaths representative results for PTA uptake over silica from a recent paper [19] are shown in Figure 6.10b. The physical limit of cationic ammine surface density thus appears to be 0.84 pmol/m2, or about 1 cationic complex/2 nm2. Cationic uptake, therefore, is inherently half of anion uptake in many cases. 

The measured uptake of CPA and PTA over the three activated carbons [55] is shown in Figure 6.28, and the trends predicted by the RPA model in Figure 6.27 are at least qualitatively observed. However, at high pH, over the two highest-surface-area carbons (CA and KB), uptake is about half of that predicted by the RPA model. The discrepancy was explained [55] by steric exclusion of the large Pt ammine complexes, believed to retain two hydration sheaths [15,19], from the smallest micropores of the high-surface-area activated carbon. 

Figure 10. Plots of the normalized selectivity coefficient (K ) for Cu in zeolite X (, o), Y (A,A) and mordenite (t,v). Empty symbols hydrated ion filled symbols amminated copper. Reproduced with permission from Ref. 123. Copyright 1980, Heyden Son Ltd.

It forms a hydrate, CoFa.2Ha0. Ammine complexes can be prepd from the hydrate Refs 1) Sax (1968), 580-L 2) CondChem-... 

ZnO films for use as buffer layers in photovoltaic cells (see Chap. 9) have been chemically deposited from aqueous solutions of ZnS04 and ammonia [57]. The solution was heated to 65°C, and adherent, compact Zn(OH)2 + ZnO films were formed after one hour. Low-temperature annealing converted the hydroxide to oxide. The solution composition will be important in this deposition. On one hand, increased ammonia concentration will increase the pH and therefore the homogeneous Zn(OH)2 precipitation in solution. However, further increase in ammonia concentration will redissolve the hydroxide as the ammine complex. There will clearly be an optimum ammonia (and zinc) concentration where Zn(OH)2 does form, but slowly enough to prevent massive homogeneous precipitation. The use of ammonia in (hydr)oxide deposition derives, in part at least, from its gradual loss by evaporation if the system is not closed [58], Any open solution of an ammonia-complexed metal ion (which forms an insoluble hydroxide or hydrated oxide) should eventually precipitate the (hydr)oxide for this reason alone. 

Isomerism in the Metal-ammines.—Werner claimed for the coordination theory that in certain cases isomerism should occur, that isomerism being brought about by different causes. lie divided isomerism in the ammines into five groups, namely, structure isomerism, ionisation isomerism, hydrate isomerism, polymerism, and stereoisomerism. 

Hydrate Isomerism.—As its name implies, this depends on the position of water in the molecule, just as in the case of the acido compounds. If two or more molecules of water are present in a molecule of ammine, the water may be present within the co-ordination complex or outside of it. For instance, the compound Cr en2.(H20)2.Br3 exists in isomeric forms. It may have all the water within the complex, in which case the formula will be [Cr en2(H20)2]Br3. In solution the whole of the bromine is precipitated by silver nitrate. On the other hand, the compound may have one molecule of water in the complex and the other outside, in which case the formula is [Cr en2(IT20)Br]Br2.H20, and only two-thirds of the bromine are precipitated by silver nitrate. Another example of this kind occurs in the cobalt series chloro-aquo-tetrammino-cobaltic chloride, [Co(NTI3)4Cl.H20]Cl2, is violet in colour, and is isomeric with dichloro-tetrammino-cobaltie chloride monohydrate, [Co(N1I3)4CI2]C1.H20, which is green. 

Although beryllium and magnesium salts do not form stable mctal-ammines yet they unite with ammonia, forming additive compounds of the hydrate type which are sometimes referred to as ammoniates or ammonio-compounds. These appear to be of the same type as the metal-anunines, and the difference seems to be merely one of stability. The ammonio-compounds are formed by the addition of ammonia gas to dry or fused salt, and most of them decompose with liberation of ammonia when dissolved in water. 

In 1893 Werner founded his new constitutional formula for inorganic compounds, applied the theory to the systematic classification of the chromi-ammines, and found that all the chromi-ammines which had been investigated could be fitted in to his system of classification. Since then the chemistry of the chromi-ammines has been further developed hv Werner, Pfeiffer, and many others relationships have been traced between chromi-ammines, complex salts, and chromic salt hydrates, and numerous cases of isomerism have been discovered in this series of ammines. 

The chromi-ammines show - very clearly the parallelism between hydrated salts and ammino-salts. It has been proved that water may be gradually substituted for ammonia in the metal-ammines, and in the hexammino-salts of chromium all degrees of substitution, with, the... 

Ammino-ferrous Sulphate.—When hydrated ferrous sulphate is heated to 115° C. it loses six molecules of water, leaving a pale yellow substance, the monohydrate, FeS04.H20. This salt readily absorbs ammonia gas, becoming reddish brown in colour with formation of pentammino-ferrous sulphate, [Fe(NH3)5]S04.H20. In vacuo the pent-ammine loses two molecules of ammonia and is converted into the diammine, [Fe(NH3)2]S04.H20. The diammine, on exposure to more ammonia, gives a triammino-derivative, [Fe(NH3)3]S04.H20, but no further absorption of ammonia takes place.2... 

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 ... 

Isomerism in Metal-Ammines—Structure Isomerism—Ionisation Isomerism— Hydrate Isomerism—Polymerism—Stereo-isomerism. 

In the single crystal absorption spectra of CrF2 and CrCl2 the pattern of spin-allowed (quintet-quintet) bands for the ammines and hydrates is repeated. Gaussian analysis of the higher wavenumber bands has allowed assignments of all three transitions and calculation of... 

Claus first postulate was vigorously attacked by Karl Weltzien (1813—1870),40 while Hugo Schiff (1834—1915)43 attacked not only Claus first postulate but also his second. All of Claus three postulates reappeared modified almost four decades later in Werner s coordination theory. Claus third postulate closely adumbrates Werner s concepts of the coordination number and of the transition series between metal ammines and metal salt hydrates. 

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