JEE Main 2025 Apr 2 Shift 2, Chemistry Q2: Colour, Magnetism And Stability Of Co-ordination Compounds

JEE Main2025Apr 2, Shift 2Chemistry

The d-orbital electronic configuration of the complex among $[Co (en)_{3}]^{3 +}$ , $[Co F_{6}]^{3 -}$ , $[Mn (H_{2} O)_{6}]^{2 +}$ and $[Zn (H_{2} O)_{6}]^{2 +}$ that has the highest CFSE is :

A
$t_{2 g}^{6} e_{g}^{0}$
B
$t_{2 g}^{6} e_{g}^{4}$
C
$t_{2 g}^{3} e_{g}^{2}$
D
$t_{2 g}^{4} e_{g}^{2}$

Solution

CFSE is maximised when the metal centre has a $d^{6}$ configuration with a strong-field ligand (low spin), since all six electrons sit in the lower-energy $t_{2 g}$ set.

Among the listed complexes, ethylenediamine (en) is the only strong-field ligand; $F^{-}$ and $H_{2} O$ are weak-field.

$Co^{3 +}$ in $[Co (en)_{3}]^{3 +}$ has the configuration $[Ar] 3 d^{6}$ , and with the SFL en it pairs up completely:

$\Rightarrow t_{2 g}^{6} e_{g}^{0}$ (low spin).

The remaining complexes use WFLs and give high-spin configurations with smaller CFSE values.

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JEE Main 2025 Apr 2 Shift 2, Chemistry Q2: Colour, Magnetism And Stability Of Co-ordination Compounds

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