In coordination compounds, There are two types of valences, primary and secondary.
primary valence is the number of negative ions which are required to satisfy the charge on the metal ion and it is written outside the coordination sphere. Primary valency is ionisable. while secondary valence are those which satisfy the coordination number of central metal ion and it is written in coordination sphere.
Take an example : [Cr(H 2 O) 6 ]Cl 3 .Here 3 chlorine atoms are outside the coordination sphere in form of 3Cl- .If the complex is ionized it will furnish Cl- as anion and Cr(H 2 O) 6 ]+3 as cation. which shows primary valency is ionisable.