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What is the correct electronic configuration of the central atom in K 4 [ F e ( C N ) 6 ] K_4[Fe(CN)_6] K 4 [ F e ( CN ) 6 ] based on crystal field theory?
medium
Coordination Compounds
2019
chemistry
t 2 g 4 e g 2 t_{2g}^4 e_g^2 t 2 g 4 e g 2
t 2 g 6 e g 0 t_{2g}^6 e_g^0 t 2 g 6 e g 0
Explanation To determine the electronic configuration of the central atom in K 4 [ F e ( C N ) 6 ] K_4[Fe(CN)_6] K 4 [ F e ( CN ) 6 ] based on crystal field theory, we need to follow these steps:
\newline 1. Identify the oxidation state of the central metal atom (Fe):
\newline
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e g 3 t 2 g 3 e_g^3 t_{2g}^3 e g 3 t 2 g 3
e g 4 t 2 g 2 e_g^4 t_{2g}^2 e g 4 t 2 g 2
• In
K 4 [ F e ( C N ) 6 ] , K_4[Fe(CN)_6], K 4 [ F e ( CN ) 6 ] , the overall charge of the complex is 0.
• Potassium (K) has a charge of +1, and there are 4 K atoms, contributing a total charge of +4.
• Cyanide (CN) is a monodentate ligand with a charge of -1, and there are 6 CN ligands, contributing a total charge of -6.
• Let the oxidation state of Fe be
The equation is:
x + 4 ( + 1 ) + 6 ( − 1 ) = 0 x + 4 − 6 = 0 x = + 2
\newline x + 4(+1) + 6(-1) = 0
\newline x + 4 - 6 = 0
\newline x = +2
\newline x + 4 ( + 1 ) + 6 ( − 1 ) = 0 x + 4 − 6 = 0 x = + 2 Therefore, the oxidation state of Fe is +2.
2. Determine the electronic configuration of Fe in the +2 oxidation state:
• The atomic number of Fe is 26, so its electronic configuration is
[ A r ] 3 d 6 4 s 2 . [Ar] \, 3d^6 \, 4s^2.
\newline [ A r ] 3 d 6 4 s 2 . • In the +2 oxidation state, Fe loses 2 electrons, resulting in
[ A r ] 3 d 6 . [Ar] \, 3d^6.
\newline [ A r ] 3 d 6 . 3. Analyze the ligand field:
• CN is a strong field ligand, which causes pairing of electrons in the d orbitals.
4. Determine the crystal field splitting and electron configuration:
• In an octahedral field, the d orbitals split into
and
levels.
• Strong field ligands like CN cause a large splitting, leading to pairing of electrons in the
orbitals.
• The 6 electrons will fill the
orbitals completely:
t 2 g 6 e g 0 . t_{2g}^6 \, e_g^0.
\newline t 2 g 6 e g 0 . Therefore, the correct electronic configuration of the central atom in
K 4 [ F e ( C N ) 6 ] K_4[Fe(CN)_6] K 4 [ F e ( CN ) 6 ] is
t 2 g 6 e g 0 . t_{2g}^6 \, e_g^0.
\newline t 2 g 6 e g 0 . This corresponds to Option 2.