28.5.1—Stability constant, Kstab, of a complex

The stability constant, Kstab, is the equilibrium constant for forming a complex ion from its constituent metal ion and ligands in a specified solvent.

A larger Kstab means the equilibrium lies further towards the coordinated complex under the stated conditions. It is an equilibrium measure, not a statement that formation is infinitely fast.

For M²⁺ + 4NH₃ ⇌ [M(NH₃)₄]²⁺, Kstab compares the equilibrium amount of the ammine complex with the free metal ion and ammonia concentrations.

Do not confuse Kstab with a rate constant or with the overall charge of the complex; a stable complex can still undergo ligand exchange.