Secondary Valence
In Werner's theory, the non-ionisable valence corresponding to the coordination number, satisfied by ligands in fixed spatial positions.
Unit
Dimensionless
In depth
Secondary valence is directional, which is why complexes have definite geometries and can show isomerism. It is satisfied by neutral molecules or anions inside the coordination sphere, and it remains constant for a given metal ion in a given oxidation state.
Examples in the real world
Cobalt(III)'s secondary valence of six, filled by six ammonia molecules in an octahedral arrangement.