Why are `Ni^(2+)` compounds thermodynamically more stable than `Pt^(2+)` compounds while `Pt^(4+)` compounds are relatively more stable than `Ni^(4+)` compounds ?

Explanation

The thermodynamic stability of transition metal compounds can be easily predicted from the values of ionisation energies. The first four ionisation energy values of nickel and platinum are given below:
`{:((E_(1)+E_(2)),E_(3)+E_(4)to,Total (E_(1)+E_(2)+E_(3)+E_(4))),(Ni 2.49MJmol^(-1), 8.80 MJmol^(-1), 11.29 MJmol^(-1)),(Pt 2.66 MJmol^(-1),6.70 MJmol^(-1),9.36 MJmol^(-1)):}`
From these values, it is clear that `Ni^(2+)` compounds will be thermodynamically more stable than `Pt^(2+)` compounds whereas `Ni^(4+)` compounds are relatively less stable than `Pt^(4+)` compounds.