Question

Incorrect order of stability is:

• A. ${\left[Co\right(ox{)}_3]}^{3-}>{\left[Co\right(H_{2}O{)}_6]}^{3+}$
• B. ${\left[Pt{F}_6\right]}^{2-}>{\left[Ni{F}_6\right]}^{2-}$
• C. ${\left[\text{Ni(trien)}\right]}^{2+}>{\left[Ni\right(en{)}_2]}^{2+}$
• D. ${\left[Ni\right(N{H}_3{)}_6]}^{2+}>\left[{\text{Ni(dmg)}}_2\right]$

Answer 1

The correct option is D ${\left[Ni\right(N{H}_3{)}_6]}^{2+}>\left[{\text{Ni(dmg)}}_2\right]$

1. ${\left[Co\right(ox{)}_3]}^{3-}and{\left[Co\right(H_{2}O{)}_6]}^{3+}$
The first compound has chelation which makes it much more stable than the second one. Hence, the given order is correct.

2. ${\left[Pt{F}_6\right]}^{2-}and{\left[Ni{F}_6\right]}^{2-}$
$Pt$ is a $5d$ series element and $Ni$ is a $3d$ series element. Since $5d$ elements have a higher CFSE than $3d$ elements, we can safely say that the first compound is more stable than the second one. Hence, the given order is correct.

3. ${\left[\text{Ni(trien)}\right]}^{2+}and{\left[Ni\right(en{)}_2]}^{2+}$
Both complexes here have chelation. However, the first one has more rings and hence it is more stable than the second one. So, the given order is correct.

4. ${\left[Ni\right(N{H}_3{)}_6]}^{2+}and\left[{\text{Ni(dmg)}}_2\right]$
DMG leads to the formation of chelation while the same phenomenon is not observed in the first complex. Hence, the given order of stability is incorrect.