Cisplatin is an anticancer drug. It is a complex of platinum(II) with the formula [Pt(NH3)2Cl2].The platinum has four ligands: two ammonia molecules and two chloride ions. Each ligand donates a lone pair to the Pt2+ ion, forming a co-ordinate bond, so the co-ordination number is 4. The complex is square planar, with bond angles of 90°.
• in the cis isomer (cisplatin) the two Cl ligands are next to each other, at 90°
• in the trans isomer (transplatin) they are opposite each other, at 180°Only the cis isomer is an effective anticancer drug. Its two Cl ligands are on the same side of the platinum, which lets it bind to DNA in the particular way needed. Transplatin cannot do this and is not used as a drug.Worked example. Show that platinum is in the +2 oxidation state. Each NH3 is neutral and each Cl− has a charge of 1−. The complex has no overall charge, so Pt + 2(0) + 2(−1) = 0, giving Pt = +2.Worked example. Calculate Mr of cisplatin (Pt = 195.1, N = 14.0, H = 1.0, Cl = 35.5): 195.1 + 2(14.0 + 3.0) + 2(35.5) = 195.1 + 34.0 + 71.0 = 300.1.
• in the cis isomer (cisplatin) the two Cl ligands are next to each other, at 90°
• in the trans isomer (transplatin) they are opposite each other, at 180°Only the cis isomer is an effective anticancer drug. Its two Cl ligands are on the same side of the platinum, which lets it bind to DNA in the particular way needed. Transplatin cannot do this and is not used as a drug.Worked example. Show that platinum is in the +2 oxidation state. Each NH3 is neutral and each Cl− has a charge of 1−. The complex has no overall charge, so Pt + 2(0) + 2(−1) = 0, giving Pt = +2.Worked example. Calculate Mr of cisplatin (Pt = 195.1, N = 14.0, H = 1.0, Cl = 35.5): 195.1 + 2(14.0 + 3.0) + 2(35.5) = 195.1 + 34.0 + 71.0 = 300.1.