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Among the following complexes, which one exhibits synergic bonding and also satisfies the Sidgwick EAN rule? (a) K[PtCl3(C2H4)] (b) K3[Fe(CN)6] (c) [Fe(H2O)5NO]SO4 (d) [Fe(CO)4]²-

1. K[PtCl3(C2H4)]
2. K3[Fe(CN)6]
3. [Fe(H2O)5NO]SO4
4. [Fe(CO)4]²-

Correct answer: K[PtCl3(C2H4)]

Solution

Synergic bonding is characteristic of pi-acceptor ligands such as CO, C2H4, and NO. Zeise's salt [PtCl3(C2H4)]- has ethylene as a synergic ligand. Whether it satisfies EAN depends on the electron count at Pt(II).

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