How many unpaired electrons are there in the strong-field complex ion, [Co(SCN)₄]²^-?

Question

Quizplus · Accepted Answer

The complex ion has a coordination number of 6 with a strong-field ligand (NCS-). Therefore, it's high-spin and we have to consider the electron configuration of cobalt as [Co(d7)]. The ion has three different types of ligands: S, P, and NCS-. The S ligands are strong-field and so contribute 2 electrons each, making a total of 4. The P ligand is weak-field and so does not split the d orbitals, contributing 0. The NCS- ligand is strong-field and donates a pair of electrons to the d orbital that is in the energy range of the NCS- lone pair. Therefore, there is one unpaired electron in the complex ion.

How Many Unpaired Electrons Are There in the Strong-Field Complex