Silver coordination number

In a linear complex, the coordination number is 2, corresponding to one group on each side of the central atom. The silver-ammonia complex, which generally forms when a very slightly soluble silver salt such as silver chloride dissolves in aqueous ammonia, is an example, as shown in Figure 22-6. Another example of a linear com-... 

Other Covalent Radii. In Cu20 and Ag20 each metal atom is equidistant from two nearest oxygen atoms, the interatomic distances corresponding to the radius values 1.18 and 1.39 A for Cu1 and Agl with coordination number two. In KAg(GN)2, in which each silver atom is similarly attached to two cyanide groups1), the effective radius of Agl is 1.36 A. It has been pointed out to us by Dr. Hoard that the work of Braekken2) indicates the presence of strings —Ag—G=N—Ag—G... 

Among the compounds that form complexes with silver and other metals are benzene (represented as in 9) and cyclooctatetraene. When the metal involved has a coordination number >1, more than one donor molecule participates. In many cases, this extra electron density comes from CO groups, which in these eomplexes are called carbonyl groups. Thus, benzene-chromium tricarbonyl (10) is a stable compound. Three arrows are shown, since all three aromatic bonding orbitals contribute some electron density to the metal. Metallocenes (p. 53) may be considered a special case of this type of complex, although the bonding in metallocenes is much stronger. 

Although 6 Is most prevalent, a coordination number of 4 Is also common, and several important complexes have a coordination number of 2. In addition, a few complexes display coordination numbers of 3, 5, and 7. Examples of coordination number 2 include the silver-ammonia complex and the gold-cyanide complex, both described in Chapter 18. To minimize ligand-ligand repulsions, a complex with a coordination number of 2 is invariably linear, as Figure 20-6 shows. 

Mononuclear silver(I) complexes with nitrogen ligands can have several coordination numbers, the simplest is dicoordinated and compounds of the type [AgL2]+ occur for a variety of ligands... 

The nitrogen in the ammonia and the oxygen in the water are the donor atoms. They are the atoms that actually donate the electrons to the Lewis acid. The coordination number is the number of donor atoms that surround the central atom. As seen above, the coordination number for Cr3+ is 6. Coordination numbers are usually 2, 4 or 6, but other values can be possible. Silver (Ag ) commonly forms complexes with a coordination number of 2 zinc (Zn2+), copper (Cu2+), nickel (Ni2+), and platinum (Pt2+) commonly form complexes with a coordination number of 4 most other central ions have a coordination number of 6. 

The small difference in energy between the s, p and d states leads to the efficient formation of s/d or s/p hybridizations, which are important for explaining the pronounced tendency of gold(I) to form linear two-coordinate complexes. This tendency for two coordination is much greater than for other isoelectronic centers, such as platinum(O), silver(I), or mercury(II), which normally yield compounds with higher coordination numbers. 

In the following presentation, solid-state structures documented hitherto for halogenocuprate(I) and halogenoargentate(I) ions are described in order of increasing coordination number of the metal, Possible correlations between the coordination number of copper(I) or silver(I) in the anion and properties of the cation with which it is coprecipitated, such as size, shape, and exposure of the positive charge, are then discussed. 

Fig. 16. The silver(I) coordination number as a function of the concentration of the halogenide ligand (mol dm3) in halogenoargentates(I) crystallizing with symmetrically substituted quaternary ammonium, phosphonium, and arsonium cations.

The properties of the N-heterocyclic complexes of silver(II) have recently been reviewed and it was found that in most complexes square planar coordination occurs about the central ion although higher coordination numbers are known.496... 

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