The Co(NH₃)₆³⁺ ion is diamagnetic, but Fe(H₂O)₆²⁺ is paramagnetic. Explain.

Interpretation: An explanation corresponding to the fact that Co(NH3)63+ ion is diamagnetic, but Fe(H2O)62+ is paramagnetic is to be stated.

Concept introduction: If a molecule contains unpaired electrons, then, it is said to be paramagnetic, whereas if a molecule does not contain any unpaired electron, then, it is said to be diamagnetic.

Weak field ligand that has small crystal field splitting energy gives high spin due to the presence of maximum unpaired electrons in lower energy t2g orbitals and higher energy orbitals.

Strong field ligand that has large crystal field splitting energy gives low spin due to the presence of maximum paired electrons in lower energy t2g orbitals.

To determine: An explanation corresponding to the fact that Co(NH3)63+ ion is diamagnetic, but Fe(H2O)62+ is paramagnetic.

Explanation

In complex ion Co(NH3)63+ , NH3 is a strong field ligand and its oxidation state is zero.

It is assumed that the oxidation state of metal ion Cobalt (Co) is x .

The given complex compound contains six Ammonia molecules. Since, the overall charge on  the complex ion is +3 . Therefore,

6(0)+x=+3x=+3

Therefore, the oxidation state of Cobalt is +3 .

Complex ion Co(NH3)63+ is diamagnetic because it does not contain any unpaired electron.

The atomic number of Cobalt (Co) is 27 and its electronic configuration is,

[Ar]3d74s2

It loses three electrons to acquire three positive charge and becomes Co3+ . The electronic configuration of Co3+ is,

[Ar]3d6

The Co3+ ion contains six d orbital electrons. Since, strong field ligand gives low spin due to the presence of maximum paired electrons in lower energy (t2g) orbitals and higher energy (eg) orbitals. Therefore, electron distribution of Co(NH3)63+ is,

t2g6eg0

It does not contain any unpaired electrons. Hence, Co(NH3)63+ is diamagnetic.

The oxidation state of Iron in Fe(H2O)62+ is +2