NH3 Complex

EDTA Must Compete with Other Ligands To maintain a constant pH, we must add a buffering agent. If one of the buffer s components forms a metal-ligand complex with Cd +, then EDTA must compete with the ligand for Cd +. For example, an NH4+/NH3 buffer includes the ligand NH3, which forms several stable Cd +-NH3 complexes. EDTA forms a stronger complex with Cd + and will displace NH3. The presence of NH3, however, decreases the stability of the Cd +-EDTA complex. 

Table 5 Calculated intermolecular distances R(Y-N) [A] of the XY- NH3 complexes as obtained with different methods applying the aug-cc-pVTZ basis set ...

Other key properties of these complexes relevant for comparison with experiment are the nuclear quadrupole coupling constants. Theoretical NQCC values, as calculated via electric field gradients, are discussed exhaustively in several recent theoretical investigations [26,28,30,33,34] and in experimental work [4-11]. BH HLYP/aug-cc-pVTZ calculated NQCCs [30,34], as evaluated for XY- -NH3 complexes, are listed in Table 10. 

Zn(H20)4+ reacts with ammonia to form the Zn(NH3) + complex ion according to the following equation ... 

There are ammoniates of PtCl2, of halides of other platinum metals and of cobalt and nickel, too, some of which have been mentioned before in, Section 50. The cobalt complexes clearly show the importance of the completed d shells for the stability of the complex. Non complex compounds of trivalent cobalt are very unstable. Solutions of divalent cobalt in ammonia, however, are readily oxidized by air, because the NH3 complex of trivalent cobalt Co(NH3)6 3+ClT has eighteen electrons used in bond formation, whereas the ion Co(NH3) + would have nineteen electrons. 

In (a) the amino groups are between 4 and 6 and between 3 and 5 in (b) they are between 4 and 5 and between 6 and 3. The broad lines represent the NH2.CH2 CH2.NH2 groups. From this it can be concluded that the six NH2 groups must octahedraliy surround the Co atom. In this way, the structure of the NH3 complexes was determined, long before the application of x-rays to structural analysis. 

Water, in its reaction with the alkali- and alkaline-earth metals, resembles ammonia, but the complexes with the halides of the platinum metals are different. The water molecule has two lone pairs of electrons, but these pairs seem to be less active in complex formation. There are many cases in which from the magnetic moment it can be concluded that the hydrates are still ionic, whereas in the corresponding NH3 complex there is covalency, the NH3 molecules sharing their lone electron-pairs with the metal atom. 

As noted by the solubility rules, most hydroxides are only slightly soluble and would be prepared as in method 1 for a salt NaOH, KOH, and NH3 are commonly available, but the choice of base must take into account the possibility that soluble OH- or NH3 complexes may form (see Table 25-1)... 

Band emission due to a Cd(3P0)-NH3 complex has been observed by Morten et al. (719) and similar bands with water, alcohols, and ethers have been observed by Yamamoto et al. (1059). 

Complexation of a C02 carbon with a free radical is a possibility, but intrinsic frequencies as high as 2346.6 cm "1 have been observed in spectra of ABP at temperatures where radical pairs have already collapsed. This does not disprove the existence of complexation in Species A1 for example, but it does show that high frequency bands can occur in the absence of radicals. Spectra of v2 provide some evidence for complexation, but analogous effects on v3 spectra have not been observed. For example, Semple has found an abnormally low bending frequency in early spectra of bis(ll-chloro-undecanoyl) peroxide, suggesting complexation between the carbon of C02 and a primary radical, but the stretching band shows no unusual shift to high frequency (T. G. Semple, personal communication). These observations are commensurate with measurements on H20 and NH3 complexes of C02 discussed in Section IV.C.3.b. 

A few crystal structures are known for Zn, i.e. Zn(N3)2(pyridine)2325 and the corresponding NH3 complex.326 In analogous Cd(N3)2(pyridine)2327 the N3 ligand is l,3-/x bridging which leads to the polymeric structure observed. The Cd center has an octahedral coordination geometry, whereas that of Zn is tetrahedral. 

It was recently reported that the nucleophilic aromatic substitution of equation 11 occurs efficiently within the photoionized van der Waals complex C6H5C1—NH3 52, an interesting case of intracluster reaction (see Section II.A.3.c). Thus, selective ionization of the van der Waals complex C6H5C1—NH3 prepared in a supersonic molecular beam led to the efficient production of C6H5NH3 and Cl via the intermediate C6H5Cl+ -NH3 complex. 

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