Explain the bonding in coordination compounds in terms of Werner's postulates.
Main postulates of Werner's theory are:
(i) In coordination compounds metals show two types of linkages (valencies) - primary and secondary.
(ii) The primary valencies are normally ionisable and are satisfied with negative ions.
(iii) The secondary valencies are non-ionisable. These are satisfied by neutral molecules or negative ions. The secondary valency is equal to the coordination number and is fixed for a metal.
(iv) The ions/groups bound by the secondary linkages to the metal have characteristic spatial arrangements corresponding to different coordination numbers.
e.g., Structure of [CoCl2(NH3)4]+Cl− is as follows: Co has 3 as Primary valency and 4 as Secondary valency.