Question

Nickel doesn't for low spin octahedral complexes why

Answer 1

first case: when the ligand is weak then there is no pairing up of electrons in the d-orbital hence there is no d-orbital for acquiring the d2sp3 hybradisation.hence low spin complexes are not formed.

second case:when the ligand is strong there is a pairing up of electrons.but there is only one vacant d-orbital available for hybradisation.so here also d2sp3 hybradisation is not formed.hence low spin octahedral complex is not formed.
thus we can concluded that nickel doesn't forms low sin octahedral complexes.

hope this helps