Ammonia ammine complexes

The participation of Cd(OH)2 in the deposition of CdS (and other metal chalcogenides) has been demonstrated or suggested on many occasions. Kitaev et al. presented a theoretical thermodynamic treatment of the Cd " /ammonia/ thiourea system to show when Cd(OH)2 should be present as a solid phase in the deposition solution [36]. A graphical representation of this analysis is shown in Eigure 3.1. This graph is based on two equilibria the solubility product of Cd(OH)2 and the stability constant of the ammonia (ammine) complex of Cd. Consider first the former ... 

Direct Titrations. The most convenient and simplest manner is the measured addition of a standard chelon solution to the sample solution (brought to the proper conditions of pH, buffer, etc.) until the metal ion is stoichiometrically chelated. Auxiliary complexing agents such as citrate, tartrate, or triethanolamine are added, if necessary, to prevent the precipitation of metal hydroxides or basic salts at the optimum pH for titration. Eor example, tartrate is added in the direct titration of lead. If a pH range of 9 to 10 is suitable, a buffer of ammonia and ammonium chloride is often added in relatively concentrated form, both to adjust the pH and to supply ammonia as an auxiliary complexing agent for those metal ions which form ammine complexes. A few metals, notably iron(III), bismuth, and thorium, are titrated in acid solution. 

Copper hydroxide is almost iasoluble ia water (3 p.g/L) but readily dissolves ia mineral acids and ammonia forming salt solutions or copper ammine complexes. The hydroxide is somewhat amphoteric dissolving ia excess sodium hydroxide solutioa to form ttihydroxycuprate [37830-77-6] [Cu(011)3] and tetrahydroxycuprate [17949-75-6] [Cu(OH) ]. ... 

We conclude with a consideration of a few other cobalt self-exchange reactions. The reaction in Eq. (9.33) is faster than that involving the ammine complexes (Eq. 9.30) because the water is a weaker-field ligand than ammonia. Thus, the activation energy for the formation of the electronically excited states is lower, as is the change in Co-ligand distances in the two oxidation states. 

Kolis et al. reported the synthesis of some metal sulfide salts of homolep-tic lanthanide ammine complexes using supercritical ammonia as a reaction medium (Scheme 12) [49]. They proposed that these reactions proceed via a... 

Whereas ligand exchange reactions in aquated complexes of Li+ have been studied extensively, the corresponding ammine complexes have so far received very little attention. The interaction of an ammonia molecule (belonging to the second coordination sphere) with [Li(NH3)4]+ is weaker than in the... 

In fact, the ammination reaction forming [Cu(NH3)4]2+ occurs stepwise, with first one ammonia ligand bonding to the copper ion, then a second, and so forth until the tetra-amminated complex is formed. And if there are four separate reaction steps, then there are four separate kinetic steps - one for each ammination step, with each reaction having its own rate constant k - we call them k(i), k(2), k(3 and k(4. This observation helps explain why the increase in reaction rate is not 16-fold when we double the concentration of ammonia. 

The ammine complexes of Co3+ are prepared by adding excess ammonia to a solution of cobalt salt followed by air oxidation and boding. The brown solution turns pink on boiling. The cyanide complexes are made by adding excess potassium cyanide to a solution of cobalt salt. Acidification of the solution with a small amount of acetic or hydrochloric acid followed by boiling yields K3Co(CN)6. The aquo-halo mixed complexes are formed by stepwise substitution of H2O molecule with halide ion in the coordination sphere. In general, a mixed complex may be prepared by substitution with a specific anion. 

Photoreduction of ammine complexes containing aliphatic amines instead of ammonia does not lead to production of molecular nitrogen instead, a variety of other ligand oxidation products are formed. Moeller and co-workers have studied three such systems in 3M HC1 solution 58 59 rather similar results have been obtained in more dilute acid solutions.55... 

Concentrated ammonium hydroxide is added to a stock solution of CdS04 (or other Cd salt). Initially, Cd(OH)2 precipitates, but this redissolves in excess ammonia to give the cadmium ammine complex ... 

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. 

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. 

Azides of complex salts with ammonia ( ammines ) are described below (p. 231). 

CA 35, 1636(1941)(Biasting expls contg AN and ammine complexes are prepd by interaction of inorg nitrates, other than those of alkali metals, with ammonia) 28)T.W, Hauff H.H.Holmes, USP 2,222,175(1940)... 

These have been known for many years.1052-1054 Chromium(III) is approximately octahedral ( ie(f = 3.69-4.1 BM) the compounds have a layer structure. In the chloride, r(Cr—Cl) is 5.76 A between layers and 3.46 A within layers. The iodide is isomorphous with the chloride and the bromide has a similar but distinct structure. All may be prepared by the direct halogenation of the metal. Other methods are available, e.g. CrCl3 may be prepared by heating Cr203-xH20 in CCU vapour at 650 °C.1055 The anhydrous halides are insoluble in water, however reducing agents such as zinc catalyze dissolution. The trichloride reacts with liquid ammonia to form ammine complexes. 

The reactions of chlorobenzene and benzaldehyde with ammonia over metal Y zeolites have been studied by a pulse technique. For aniline formation from the reaction of chlorobenzene and ammonia, the transition metal forms of Y zeolites show good activity, but alkali and alkaline earth metal forms do not. For CuY, the main products are aniline and benzene. The order of catalytic activity of the metal ions isCu> Ni > Zn> Cr> Co > Cd > Mn > Mg, Ca, Na 0. This order has no relation to the order of electrostatic potential or ionic radius, but is closely related to the order of electronegativity or ammine complex formation constant of metal cations. For benzonitrile formation from benzaldehyde and ammonia, every cation form of Y zeolite shows high activity. 

Jones and Landis (12) assumed the formation of the ammine complexes and their participation in the reaction of toluene with ammonia to form benzonitrile over a variety of transition metal-exchanged X zeolites. 

With this situation in mind, the formation constant (ft) of the first ammonia molecule making the coordination bond with metal cations was taken as the measure of the ease of ammonia adsorption on metals. The values of (ft) were taken from Ringbom s table (H). The plot of the catalytic activity against formation constants of ammine complexes is shown in Figure 2. The correlation is good except for CdY. Again, the metals with lower formation constant (Na+, Ca+, Mg2+) have no activity for chlorobenzene reaction. 

The reaction of PtX and liquid ammonia gives mixtures of haloammine complexes [PtX (NH3)6 ]X4 n (X = Cl, Br, I n = 3, 2, 1, 0). The salts Pt(NH3)6]X, may be isolated as the main product only after several weeks of reaction. Interactions at room temperature of PtCl -and PtBr salts with liquid ammonia yield the dinuclear p-amido ammine complex [(NH3)4Pt(/i-NH2)2Pt(NH3)4]X6 quantitatively.1033 The structure shows a Pt-Pt separation of 3.16(1) A. 34 Interaction of PtXg with liquid or gaseous ammonia followed by addition of excess KNH2 yields the hexakis(amido) complex K2[Pt(NH2)6] (equation 333).1033 Complexes of the anionic ligand NC12 bonded to platinum(IV) have also been prepared. One method is by treatment of [PtCl(NH3)s]CI3 with chlorine (equation 334).1035... 

A wide variety of zinc and cadmium complexes are formed from these ligands and in some cases, e.g. that of ammonia and the ammine complexes, they have a long history.2,3 6 8 They have been widely studied both in the solid state and in solution.6,23,24 Here attention is drawn to some recent developments.9 15,1468c h... 

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