Metal ions coordination numbers

Compound Ref. Average M—C Bond Length (A) Formal Metal ) Ion Coordination Number Metal lonict) Radius (A) Efiective COT Ionic Radius (A)... 

Metal ion Coordination number Polyhedron type Schematic presentation... 

FIGURE 15.6. Some coordination polyhedra. M = metal ion, L— ligand. Shown are polyhedra for metal ions coordination number 2 (linear), 3 (trigonal planar, trigonal pyramidal), 4 (tetrahedral, square planar), 5 (square pyramidal, trigonal bipyrami-dal), 6 (octahedral, trigonal biprismatic), 7 (pentagonal bipyramidal) and 8 (square antiprismatic). 

Table 1. Metal Ion Coordination Number, Ionic Radius, and Charge Density.

The D and A pathways proceed through intermediates of reduced and increased coordination numbers, respectively. The I mechanisms are characterized by the lack of an intermediate with a modified metal ion coordination number in the reaction. When bond breaking is more important than bond making the mechanism is Id the transition state has a reduced coordination number. In an Ia mechanism bond making is more important than bond breaking the transition state has an increased coordination number. 

Metal Ion Coordination Number Geometry Ligand Atom D<... 

The lowest line is formed by the MO2 oxides of electron metals with Cap2-type cubic structure with metal ion coordination number 8. The parameters a and 3 of the linear functions ... 

Studies of metal ion coordination with anion ligands in mixed organic/aqueous solvent systems have provided novel information about the metal ion coordination numbers and mechanism of crystallization processes from Raman spectroscopy. Also, thermodynamic parameters such as enthalpy of band formation or breakage have been evaluated from Raman spectra of solution studied over a range of temperatures. 

Many other shapes are possible for complexes. The simplest are linear, with coordination number 2. An example is dimethylmercury(O), Hg(CI l,)2 (4), which is a toxic compound formed by bacterial action on aqueous solutions of I Ig ions. Coordination numbers as high as 12 are found for members of the / block, but they are rare in the d block. One interesting type of d-mctal compound in which there are 10 links between the ligands and the central metal ion is ferrocene, dicyciopentadi-enyliron(O), [Fe(C5H5)2] (5). Ferrocene is an aptly named sandwich compound, with the two planar cyclopentadienyl ligands the bread and the metal atom the filling. The formal name for a sandwich compound is a metallocene. 

Much of what has been said so far in this chapter applies equally well to complexes of second- and third-row transition metals. However, there are some general differences that result from the fact that atoms and ions of the second- and third-row metals are larger in size than those of first-row metals. For example, because of their larger size (when in the same oxidation state as a first-row ion), ions of metals in the second and third rows form many more complexes in which they have a coordination number greater than 6. Whereas chromium usually has a coordination number of 6, molybdenum forms [Mo(CN)8]4 and other complexes in which the coordination number is 8. Other complexes of second- and third-row metals exhibit coordination numbers of 7 and 9. 

Rationalization of the detailed geometry of the particular halogeno-cuprate(I) or halogenoargentate(I) ion in terms of the influence of cation shape or positive charge distribution is, however, much more complex. Whereas it has proved possible to employ cations predictively for anion design in series of compounds containing comparable cations, e.g., symmetrically substituted tetraalkylammonium and phosphonium analogs (cf. 60, 71, 72), it seems doubtful that cations of disparate shape can be used as other than predictors of metal(I) coordination number. 

Another term you should be familiar with is the coordination number of the metal ion. This number refers to the total number of bonds formed with the ligands. In the Fe(CN)e4- ion, iron has formed 6 bonds (one with each cyanide), so the coordination number of iron in this complex is 6. 

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