Chlorophyll is a coordination compound of magnesium (Mg) responsible for photosynthesis in plants.HaemoglobinIt is a coordination compound of iron (Fe) and it regulates the respiration process. Haemoglobin and hemoglobin–like molecules are also found in many invertebrates, fungi, and plants.
When the metal in the coordination compound (in solution) retains its identity, the compound is called metal complex. For example, copper in hydrated tetra-amino cuprous sulphate solution.
Stability of compounds:
It is referred to the degree of association between metal and ligands at equilibrium.
Example: Formation of cuprammonium ion.
The addition of four amine groups to copper takes place in four stages. The change in concentration of solution at each stage is given by formation constant [Kx] and is expressed as log Kx where x denotes number of stage. The corresponding formation constants calculated on experimental data are: log K1 = 4, log K2 = 3.2, log K3 = 2.7 and log K4 = 2. The overall stability of metal complex is given by association constant (β).
The summation of individual formation constants gives degree of associatino, a measure of stability of complex. log β = Σ log Kx = 11.9.
The reciprocal of formation constant gives dissociation constant (measure of instability) of coordination complex.