Question

Explain the application of VBT to hexamine cobalt $(III)$ ion ${{[Co{{(N{{H}_{3}})}_{6}}]}^{3+}}$

Answer 1

Valence bond theory is a theory which is used to explain chemical bonding. It tells us about how the atomic orbitals combine to give individual chemical bonds. Strongest bond is formed when there is a maximum overlap of atomic orbitals.

Complete step by step answer:
As you can see that, ${{[Co{{(N{{H}_{3}})}_{6}}]}^{3+}}$ , it is a metal amine complex, in which cobalt ion is attached with six ammonia ligands.
Valence bond theory says that a formation of covalent bond takes place between the overlapping of two atoms, having half – filled valence atomic orbitals, in which each atom contains one unpaired electron.
As you can see that, ${{[Co{{(N{{H}_{3}})}_{6}}]}^{3+}}$ , coordination number of central metal ion is six. Coordination number six results in two possible hybridization, that are, ${{d}^{2}}s{{p}^{3}}$ and $s{{p}^{3}}{{d}^{2}}$ . Both the hybridization gives octahedral geometry. $N{{H}_{3}}$ is a strong ligand, ${{[Co{{(N{{H}_{3}})}_{6}}]}^{3+}}$ is an inner orbital complex. In this complex, the six valence electrons of cobalt will occupy $3d$ orbital, whereas these ligands will occupy $3d,4s$ and $4p$ orbitals, that gives ${{d}^{2}}s{{p}^{3}}$ hybridization.
As we know that, electronic configuration of $Co$ is $Ar\,3{{d}^{7}}\,4{{s}^{2}}$
Electronic configuration of $C{{o}^{+3}}$ is $Ar\,3{{d}^{6}}$
In presence of strong ligands $N{{H}_{3}}$ it will attract an inner $d$ orbital for bonding. As we discussed, the coordination number of $C{{o}^{+3}}$ is six, so it will require six empty atomic orbitals to receive coordinated lone pairs of electrons. Hence, two $3d$ orbitals, three $4p$ orbitals, and one $4s$ orbital are combined to give ${{d}^{2}}s{{p}^{3}}$ hybridization.

So, the correct answer is Option A .

Note: 1.In ${{[Co{{(N{{H}_{3}})}_{6}}]}^{3+}}$ , oxidation state of cobalt is $+3$ .
2.$N{{H}_{3}}$ is a strong ligand, which causes the pairing and cobalt undergoes ${{d}^{2}}s{{p}^{3}}$ hybridization.
3.Here, the electronic configuration of cobalt is ${{d}^{6}}$ .
4.This molecule is diamagnetic because six pairs of electrons from each ammonia molecule occupy six hybrid orbitals.