The exhibition of the highest co-ordination number depends on the availability of vacant orbitals in the central atom. Which of the following elements is not likely to act as central atom in MF₆^3-?

The element M in the complex-ion MF₆^3- has a coordination number of six.

Boron has only s- and p-orbitals and no d – orbitals.

Therefore, at the maximum, it can show a coordination number of 4. Thus, B cannot form a complex of the type MF₆^3-.