JEE Main 2020 — Coordination Compounds Question with Solution

(I) [Cr(H₂O)₆]Br₂

H₂O is weak field ligand so it can not pair up all the electrons.

Cr²⁺ : [Ar] 4s⁰3d⁴ ($$t_{2g}^{3}e{g}^1$$)

Unpaired e^– = 4

Magnetic moment = $$\sqrt{24}$$ = 4.89 BM

(II) Na₄[Fe(CN)₆]

CN^- is strong field ligand so it pair up all the electrons.

Fe²⁺ = [Ar] 4s⁰3d⁶ ($$t_{2g}^{6}e{g}^0$$)

Unpaired e^– = 0

Magnetic moment = 0 BM

(III) Na₃[Fe(C₂O₄)₃]

As $$\Delta$$₀ $$>$$ P, so pairing of electrons happens.

Fe³⁺ = [Ar] 4s⁰3d⁵ ($$t_{2g}^{5}e{g}^0$$)

Unpaired e^– = 1

Magnetic moment = $$\sqrt{3}$$ = 1.73 BM

(IV) (Et₄N)₂[CoCl₄]

Cl^-is weak field ligand so it can not pair up all the electrons.

Co²⁺ = [Ar] 4s⁰3d⁷ ($$e{g}^4{t}_{2g}^3$$)

Unpaired e^– = 3

Magnetic moment = $$\sqrt{15}$$ = 3.87 BM

Hence order of magnetic moment is
I > IV > III > II