The increasing order of stability for the following complexes will be:
A. \([Cu(NH_3)_4]^{2+}\)
B. \([Cu(CN)_4]^{2-}\)
C. \([Cu(en)_2]^{2+}\)
D. \([Cu(H_2O)_4]^{2+}\)
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → \(D < A < C < B\)
The stability of a complex of the same metal ion depends on how strongly the ligands bind to it. Two points decide the order here:
Ligand strength: \( \ce{H2O} \) is a weak ligand; \( \ce{NH3} \) is a stronger σ-donor; \( \ce{CN^{-}} \) is a strong-field ligand that forms very strong bonds (it is also a π-acceptor).
Chelate effect: ethane-1,2-diamine (en) is a didentate ligand; two en molecules bind through four N atoms and close two five-membered rings. A chelate is more stable than a complex with the same donor atoms from unidentate ligands, so \( \ce{[Cu(en)2]^{2+}} \) is more stable than \( \ce{[Cu(NH3)4]^{2+}} \).