Question

Why platinum forms the square planar while chromium and nickel forms tetrahedral?

Answer 1

A good general rule is that if you have either square planar or tetrahedral, a low-spin complex generally forms square planar, and a high-spin complex generally forms tetrahedral. Platinum is not an exception to that statement.

     Platinum has bigger  d -orbitals than nickel does, which can hold more electron density more capably, because the electron density can be more spread out in a larger  d -orbital.

Therefore, platinum can support a higher-energy structure such as the square planar structure.

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