Step 4. Build PtCl₄H₂^2-

The following is a picture of the whole molecule. The colors of the Cl-atoms have been changed for clarity:

To make this molecule, an easy way is to start with an octahedral complex to ensure symmetry. Next make changes to get this molecule, ending with a geometry optimization with ADF:

Build an octahedral metal complex using the Structures button
  (Metal Complexes>ML6 octahedral)
Change the central atom into a Pt atom
Change four dummies in a plane into Cl atoms
Change the Cl atom color (use the pop-up menu)
Remove one of the remaining dummies
Change the remaining dummy in OH
  (this will ensure the final two H's do not break symmetry)
Change the O atom into an H atom

(optionally) Preoptimize

Choose the 'Geometry Optimization' Preset
Set the total charge to -2 (in the Charge and Spin panel)
Select the scalar ZORA relativistic option (in the Relativity panel)

Run

When the run has finished, click 'yes' to import the optimized coordinates
Save