Factors Affecting The Stability Of Complexion

(a) Nature of central metal ion:

The higher the charge density on the central metal ion, the greater is the stability of the complex. In other words, the greater the charge and smaller the size of an ion (i.e. charge/radius of an ion), the greater is the stability of its complexes. For example, the stability constant of is much greater than the stability constant of [Fe(CN) ₆ ] ^4- .

; K = 1.8 ×

Fe ³⁺ + 6CN ^- K = 1.2 ×

(b) Nature of the ligand:

Greater the base strength of a ligand, the greater is the ease with which it can donate its lone pair of electrons and therefore, greater is the stability of the complexes formed by it.

For example, ; K = 4.5 ×

; K = 2.0 ×

These values suggest that stability constant of is more than that of because CN− is strongly basic ligand than the NH3.

(c) Presence of Chelate Ring:

Chelating ligands form more stable complexes as compared to monodentate ligands.

For example,

Ni ²⁺ + 6NH ₃

[ Ni(en) ₃ ] ²⁺ ; k =4 × 10 ⁸

The above values clearly indicate that chelated complexes are much more stable than non−chelated complexes.

Also Check

• Co-Ordination Chemistry
• Transition Elements