What is the hybridization of sb in the molecule sbcl52–? antimony (sb) can accept up to twelve electrons?

The valence electron configuration for antimony (Sb) is:

Sb = 5s²5p³5d⁰

In SbCl₅²⁻, antimony has a -2 charge i.e. it has 2 additional electrons

Sb²⁻ = 5s²5p⁵5d⁰

Following a two electron transition from p→d orbital we have:

Sb²⁻ = 5s²5p³5d²

There is a total of 5 unpaired electrons (3 in the p and 2 in the d) which can form five bonds with the 5 Cl atoms.

Thus the hybridisation of Sb in SbCl₅²⁻ is sp³d²