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Among the following four nickel and zinc complexes, three share the same geometry. Which one has a geometry different from the other three?

1. [NiCl4]²-
2. Ni(CO)4
3. [Ni(CN)4]²-
4. [Zn(NH3)4]²+

Correct answer: [Ni(CN)4]²-

Solution

[Ni(CN)4]²- adopts a square planar geometry (dsp² hybridization) because CN- is a strong-field ligand that pairs all d electrons in Ni²+ (d⁸). The other three complexes — [NiCl4]²-, Ni(CO)4, and [Zn(NH3)4]²+ — are all tetrahedral (sp³).

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