Stepwise Formation Constant
The equilibrium constant for the addition of one further ligand to a partially formed complex.
Formula / equation
K₁, K₂, K₃ …
Unit
Various
In depth
Complexes build up one ligand at a time, and each step has its own constant. Successive values almost always decrease, because statistical factors and increasing steric and electrostatic crowding make each additional ligand harder to attach than the last.
Examples in the real world
For [Cu(NH₃)₄]²⁺ the four constants fall from about 10⁴·¹ to 10²·⁰.