Other Ammine Complexes

2 Effect of methanol cosolvent on the energetics of the activated complex in the reduction of the complex by ascorbic acid in methanol/aqueous solution As discussed in Sec. 13.7.3, can be calculated from energetics of a reaction in 2 solvents and from AG r, for the reactants from one solvent to another. When a series of mixed solvents are used, the trend in the stabilisation/destabilisation of die transition state compared to the reactants can be determined. This may shed some light on the transition state. 

The kinetics of the reactions in methanol/water mixtures can be followed in the same way as the reduction in water discussed above. Prepare solutions of the complex and of ascorbic acid in the following solvents 25% v/v methanol in water, 40% v/v methanol in water, 50% v/v methanol in water and 40% v/v ethanol in water. Use a temperature range of 10 C-20 C and calculate the free energy of activation in each case and compare it with the corresponding value in water. 

Determination of the solubility of ascorbic acid in the above solvents Since Mn(HI) sulphate solutions react rapidly with ascorbic acid solution (Sec. 12.4.1), the solubility of ascorbic acid can be determined by titrating a known volume of the saturated solution at 298 K. 

Numerous complexes of Co(III) containing en as the only ligand or with other ligands have been prepared and studied. Similarly other diamines form complexes with Co(III), the nearest to en is pn (1,2-propanediamine). 

---

Table 111-2. Infrared Frequencies of Other Ammine Complexes (cm" )... 

When ammonia is added to a solution of a copper(II) salt, there is a rapid reaction in which water coordinated to Cu is replaced by ammonia. Although the product of this reaction is normally represented as [Cu(NH3)4], in fact, a variety of products result, the relative amount of each species depending upon the concentrations of copper(n) ion and ammonia reactions (1) to (4). Figure 5.1 is a plot of the percentage of each copperfll) ammonia species in solution against the concentration of free ammonia. This plot indicates that [Cu(NH3)4(H20)2] is the predominant complete ion in solutions containing 0.01 to 5 M free ammonia. Outside this range, however, the other ammine complexes are more abundant. 

The ir spectra are reported in the above references. The ir spectrum of [Ni(NH3)6] will be similar to other ammine complexes. 

Simple nickel salts form ammine and other coordination complexes (see Coordination compounds). The octahedral configuration, in which nickel has a coordination number (CN) of 6, is the most common stmctural form. The square-planar and tetrahedral configurations (11), iu which nickel has a coordination number of 4, are less common. Generally, the latter group tends to be reddish brown. The 5-coordinate square pyramid configuration is also quite common. These materials tend to be darker in color and mostiy green (12). 

Cobalt exists in the +2 or +3 valence states for the majority of its compounds and complexes. A multitude of complexes of the cobalt(III) ion [22541-63-5] exist, but few stable simple salts are known (2). Werner s discovery and detailed studies of the cobalt(III) ammine complexes contributed gready to modem coordination chemistry and understanding of ligand exchange (3). Octahedral stereochemistries are the most common for the cobalt(II) ion [22541-53-3] as well as for cobalt(III). Cobalt(II) forms numerous simple compounds and complexes, most of which are octahedral or tetrahedral in nature cobalt(II) forms more tetrahedral complexes than other transition-metal ions. Because of the small stabiUty difference between octahedral and tetrahedral complexes of cobalt(II), both can be found in equiUbrium for a number of complexes. Typically, octahedral cobalt(II) salts and complexes are pink to brownish red most of the tetrahedral Co(II) species are blue (see Coordination compounds). 

Compounds of Tl have many similarities to those of the alkali metals TIOH is very soluble and is a strong base TI2CO3 is also soluble and resembles the corresponding Na and K compounds Tl forms colourless, well-crystallized salts of many oxoacids, and these tend to be anhydrous like those of the similarly sized Rb and Cs Tl salts of weak acids have a basic reaction in aqueous solution as a result of hydrolysis Tl forms polysulfldes (e.g. TI2S3) and polyiodides, etc. In other respects Tl resembles the more highly polarizing ion Ag+, e.g. in the colour and insolubility of its chromate, sulfide, arsenate and halides (except F), though it does not form ammine complexes in aqueous solution and its azide is not explosive. 

It exists as optical isomers and was first resolved by Alfred Werner. The route to the bis complexes generates the ammine in situ and is applicable to other ammines (tren, trien, etc.) yielding principally the trans-isomer... 

The soft Au+ forms relatively few complexes compared with those of phosphines. Complexes with ammines, nitriles and diazoles like Au(NH3)2 and Au(RCN)2 are known but little studied. In linear Au(NH3)2, Au-N is 2.01-2.03 A [70a], [Au(NCPh)2]+ has been used as a labile source of other gold complexes [70b]. AuCl(piperidine) is a monomer with weak tetra-meric association in contrast AuX(py) (X = Cl, Br, I) are [Aupy2]+[AuX2] with a chain structure in the solid state (and Au-Au interactions), suggesting a close balance between factors for molecular and ionic structures [70c] (note also the tetrahydrothiophene complexes in section 4.10.6). 

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. 

On the other hand, reduction of (H20)5Cr(NC5H4X) by Ru(bpy)3 has an associated value for p of 1.1, the same as for the Co and Ru ammine complexes and therefore a similar mechanism. For other applications of Hammett LFER see Refs. 141-144. 

Large cations, such as the afore mentioned ammine complexes or organic cations like tetraphenylarsonium or tetrabutylammonium, have practically no influence on the internal vibrations of the anion. On the one hand the classical polarizing effect of the cation would be decreased because of the greater radius on the other hand, the large volume of the cation screens the anion so that all the lattice interactions would be decreased. Usually, in such cases, sharp and very clear anion bands are found, indicating screening (110, 115). 

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 ... 

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 ... 

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. 

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)... 

Many analogues of the dinuclear ammines (Table 47) are known in which ammonia molecules may be considered replaced by ethylenediamine and other bidentate ligands (Table 52). The inter-relations among the complexes are similar to those in Schemes 35 and 36. There are additional examples in the review by Gamer and House302 and other bridged complexes are covered in Sections 35.4.1.1, 35.4.2.3.vi, 35.4.2.4, 35.4.2.5, 35.4.4.2, 35.4.4.10, 35.4.7.4 and 35.4.8.3. Cyano-bridged complexes are listed in Table 45. 

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 chlorides of the other polyhasic ammine complexes with cobalt described in (II) may easily be prepared in solution by a similar procedure, but only the ethylenedi-amine compound can be directly isolated as a solid. The other chlorides must be made indirectly from the nitrates, bromides, or iodides of the respective series,... 

Hydrolysis of ammonia or amines is often observed, but only in a few cases have such reactions proved to be useful synthetically. Base hydrolysis (aqueous NH3) of the so-called rhodo ion, (NH3)5Cr(OH)-Cr(NH3)55 +, yields the so-called cis hydroxo erythro ion, cis-(NH3)5-Cr(OH)Cr(NH3)4(OH)4+, and both this ion and its corresponding acid form, cis aqua erythro have been isolated as salts (227, 252, 253). The hydrolysis is complete within minutes, and unlike the hydrolysis of many other ammine chromium(III) complexes, is quite a clean reaction, at least in solutions of moderate alkalinity (225). The corresponding trans aqua isomer has been prepared by heating the solid... 

---