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For the following coordination compounds, match each complex with the set of d-orbitals that have the highest energy in its crystal field splitting diagram. Complex: (A) [Ni(CN)4]²-, (B) [NiCl4]²-, (C) [Cr(en)3]Cl3, (D) [PtCl4]²-.

1. [Ni(CN)4]²- has d_xy and d_z² as highest energy orbitals
2. [NiCl4]²- has dₓ²-y² and d_z² as highest energy orbitals
3. [Cr(en)3]Cl3 has dₓ²-y² and d_z² as highest energy orbitals
4. [PtCl4]²- has d_xy, d_yz, d_xz as highest energy orbitals

Correct answer: [Cr(en)3]Cl3 has dₓ²-y² and d_z² as highest energy orbitals

Solution

Geometries and highest-energy d-orbitals: - [Ni(CN)4]²-: square planar (CN- strong field, Ni²+ d⁸). Highest energy: dₓ²-y² (only one orbital is highest in square planar). Not d_xy and d_z². - [NiCl4]²-: tetrahedral (Cl- weak field, Ni²+ d⁸). In tetrahedral field, the t2 set (d_xy, d_xz, d_yz) is higher; dₓ²-y² and d_z² are in the e set (lower). So option B is wrong. - [Cr(en)3]³+: octahedral (en strong field, Cr³+ d³). In octahedral field, e_g set (dₓ²-y², d_z²) are highest. Option C is CORRECT. - [PtCl4]²-: square planar (Pt²+ d⁸). Highest: dₓ²-y² alone, not d_xy, d_yz, d_xz.

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