= Solution
<cisplatin> has <square planar molecular geometry> and a $5d^8$ <metal> centre. Choose $x$ and $y$ along the four Pt–donor directions. The strongly antibonding $d_{x^2-y^2}$ orbital is highest and remains empty; the other four <d orbitals> are doubly occupied. The <square-planar splitting> is represented by the conventional qualitative order
$$
(d_{xz},d_{yz})^4\,(d_{z^2})^2\,(d_{xy})^2\,(d_{x^2-y^2})^0.
$$
The ordering among the lower occupied levels can depend on the ligand set, and the cis arrangement removes exact fourfold symmetry. The robust result is the filled lower four levels and empty highest level.
<satraplatin> has approximately <octahedral molecular geometry> around Pt(IV), $5d^6$. Its large <octahedral splitting> favours a <low-spin complex>:
$$
\boxed{t_{2g}^6e_g^0.}
$$
All three $t_{2g}$ orbitals are paired. Mixed ligands remove exact degeneracies, but do not change this qualitative occupancy.
\Image[/past-exam-of-the-chemistry-b-course-of-the-university-of-cambridge/2023/paper-2-fields.png]
{title=Filled and empty d orbitals for the square-planar d8 and octahedral low-spin d6 platinum centres}
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