Stability of a compound can be explanined on the basis of its lattice energy `(Delta_(U)H^(Θ))` which is inversely proportional to the sum total of the radius of cation and anion.
Lattice energy `prop (1)/(r_(o+)+r_(Θ))`
Since `Li^(o+)` ion is exceptionally small in size, it will form stable complexes with small size anion, due to high lattice energy of the compound formed, whereas compound of `Li^(o+)` ion with large size anion `CO_(3)^(2-)` and `NO_(3)^(Θ)` are relatively less stable due to the less lattice energy.