JEE Main · 2021 · 25 Jul 2021 · Shift 2 · Coordination Compounds

Which one of the following metal complexes is most stable? [coordination-complex formulas shown as options in source]

(A) $[Co (en)_{2} (N H_{3})_{2}] C l_{2}$
(B) $[Co (N H_{3})_{6}] C l_{2}$
(C) $[Co (en)_{3}] C l_{2}$ ✓ Correct
(D) $[Co (en) (N H_{3})_{4}] C l_{2}$

Answer: (C)

Solution

Stability of a complex rises with the number of chelate rings (chelate effect).

[Co (en)_{3}]^{2 +}

has three ethylenediamine chelate rings — the most of the four — so it is the most stable; the bis- and mono-en species have fewer rings and

[Co (N H_{3})_{6}]^{2 +}

has none.

JEE Main · 2021 · 25 Jul 2021 · Shift 2 · Single correct option

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