Ammonia ligand

Water has two lone pairs of electrons. Once one of these is used to form the cr-bond to the metal ion, the second may be used to form a iT-bond. This causes the f2g set of orbitals to move up in energy, making A() smaller therefore, water is a weak-field ligand. Ammonia does not have this extra lone pair of electrons and consequently cannot function as a tt-donor ligand. 

A species that bonds to a metal cation to form a complex is known as a ligand. Any species that has a lone pair of electrons has the potential to be a ligand, but in this section, we confine our description to a few of the most common ligands ammonia, compounds derived from ammonia, cyanide, and halides. We describe additional examples in Chapter 20 which addresses the chemistry of the transition metals. 

In addition to water molecules the coordination chemistry of leaching generally involves simple inorganic anionic ligands, ammonia, or acetonitrile. Many of the well-established processes (see Table 2) were considered in CCC (1987),4 and are also described in a recent comprehensive text on hydrometallurgy.2... 

The initial entry of Chapter 3 proves that sophisticated ligands are not a requirement for useful coordination complexes. An alternative synthesis is offered for cisplatin, the widely used anticancer chemotherapeutic agent which contains the ultimate neutral ligand, ammonia. The coordination complexes of Chapter 3 traverse the periodic table and provide a number of... 

Among N-donor ligands, ammonia, aliphatic, aromatic, and heterocyclic amines are widely used as ligands at present (see Sec. 2.2.4.2). Amine complexes are obtained by direct (immediate) interaction of ligands and metal salts, for example (3.8) [8] ... 

An important application of the trans effect is the synthesis of specific isomers of coordination compounds. Equations (3) and (4) show how the cis and trans isomers of Pt(NH3)2Cl2 can be prepared selectively by taking advantage of the trans effect order Cl > NH3. This example is also of practical interest because the cis isomer is an important antitumor drug, but the trans isomer is ineffective. In each case the first step of the substitution can give only one isomer. In equation (3) the cis isomer is formed in the second step because the Cl trans to Cl is more labile than the Cl trans to the lower trans effect ligand, ammonia. On the other hand, in equation (4) the first Cl to substitute labilizes the ammonia trans to itself to give the trans dichloride as final product. 

Rule 4. Order within Classes of Ligands. Ammonia is listed last among the neutral groups. 

Rgure 1.Two ligands (ammonia) each donate a pair of electrons to bond with a silver ion. (N = nitrogen, H = hydrogen, Ag = silver.) Illustration Hans Cassidy. Courtesy of Gale Group. 

Molecules that exhibit stereochemical non-rigidity are said to display fluxional character. All molecules undergo vibrations about an equilibrium position that does not alter their average spatial location for a limited number, however, rearrangement that changes the configuration can occur. One of the commonest ligands, ammonia, is a simple example of the concept (Equation 5.49), since as a pyramidal molecule it can invert. 

OSO3NR NH3 and OSO3NR, and the pre-equilibrium reaction of OSO3NR with the model ligand ammonia (AG). 

The formation of silver oxide and its dissolution in the presence of ammonia is slightly more complicated than the preceding case. The ligand ammonia NH3 is basic. Not only does the superimposition of precipitation and complexation phenomena occur,... 

A chloride ligand in rrans-[Co(en)2Cl2]CI (Sec. 14.8.1) can be readily replaced by other ligands. Ammonia or nitrite can easily replace the chloride. Since they are both higher in the spectrochemical series, the ligand exchange is accompanied by a change in the absorption spectrum and the colour of the complex. 

The reader s indulgence is asked for the inclusion here of an inor-ganic reaction, illustrating the effect of JV-deuteration in an ammonia molecule that remains bound during the reaction. Complete deutera-tion of the ligand ammonia molecules in the aquation reaction ... 

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