Coordination Number 4

Two different geometries are possible. The tetrahedron is the more common while the square planar is found almost exclusively with metal ions having a d⁸ electronic configuration.

• Tetrahedral Geometry: The chemistry of molecules centered around a tetrahedral C atom is covered in organic courses. To be politically correct, please change all occurrences of C to Co. There are large numbers of tetrahedral Cobalt(II) complexes known.

Figure 1: CoCl₂pyr₂

• Square Planar Geometry: This is fairly rare and is included only because some extremely important molecules exist with this shape.

Figure 2: cisplatin - cis-PtCl₂(NH₃)₂