Cis-platin is a neutral complex of platinum(II) with the chemical formula . It consists of a central platinum ion coordinated to two ammonia () ligands and two chloride () ligands.
Unlike many four-coordinate complexes that adopt a tetrahedral shape, cis-platin exhibits a square planar geometry. This occurs because the electronic configuration of favors a flat arrangement where the ligands occupy the corners of a square.
The bond angles in this square planar arrangement are exactly . This specific spatial orientation is critical for its biological activity and interaction with cellular targets.
The coordination number of the central platinum ion is 4, as it forms four dative covalent (coordinate) bonds with its surrounding ligands.
The primary goal of cis-platin is to trigger apoptosis (programmed cell death) in cancer cells by making their DNA unreadable and unreplicable. This is particularly effective against fast-growing tumors.
However, the drug is not perfectly selective. It also binds to the DNA of healthy cells that replicate quickly, such as those in hair follicles, the lining of the gut, and bone marrow.
This lack of total selectivity leads to common side effects including hair loss, nausea, and suppressed immune function. Modern research focuses on delivery systems that target the drug more specifically to malignant tissue.
| Feature | Cis-platin | Trans-platin |
|---|---|---|
| Ligand Arrangement | Identical ligands on the same side | Identical ligands on opposite sides |
| Biological Activity | Highly effective anti-cancer drug | Biologically inactive/ineffective |
| DNA Interaction | Forms intra-strand cross-links | Cannot form effective intra-strand links |
| Bond Angle (Cl-Pt-Cl) |
Drawing Structures: When asked to draw cis-platin, always ensure the two atoms are adjacent. Use wedges and dashes if necessary to show the flat plane, though a simple 2D square representation is often sufficient if labeled correctly.
Identifying Geometry: Remember that and complexes with four ligands are almost always square planar, not tetrahedral. This is a common trap in coordination chemistry questions.
Mechanism Steps: Be prepared to describe the sequence: 1. Diffusion into cell, 2. Substitution of by , 3. Binding to nitrogen on DNA bases.
Charge Awareness: Note that cis-platin itself is a neutral molecule (). The oxidation state of Pt is , which is balanced by the two charges of the chloride ligands.
