Solution

The anticancer drug cisplatin is cis-diamminedichloridoplatinum(II), cis-$[Pt(NH_3)_2Cl_2]$.
It is a square planar complex in which the two $NH_3$ ligands are adjacent (cis) and the two $Cl^-$ ligands are adjacent.
Inside the cell the Cl ligands are replaced by water, and the platinum binds to two neighbouring guanine bases of DNA. This cross-linking distorts the DNA and stops replication of the rapidly dividing cancer cells.
The trans isomer cannot bind to two neighbouring bases in this way and is not an effective anticancer drug.
$[PtCl_4]^{2-}$ and Zeise's salt anion $[PtCl_3(C_2H_4)]^-$ are not used as anticancer drugs.
So the anticancer species is the cis isomer of $[Pt(NH_3)_2Cl_2]$ (cisplatin).

Concept Cisplatin as anticancer drug

Coordination Compounds in past papers

104 questions from this chapter have appeared across 27 exam years.