Why do we want to know the structure for a coordination compound? The compound's structure (i.e., how the ligands are arranged around the metal atom) determines its physical and chemical properties. For example, a tetrahedral compound will behave differently than a square planar compound that contains the same metal atom and the same ligands.
Consider the complex ion, [CoCl4]2-. The coordination number of [CoCl4]2- is equal to 4; thus, the structure of [CoCl4]2- might be:
|A Comparison of Tetrahedral and Square Planar Structures|
CN = 4
ligands attached at the corners of a tetrahedron
CN = 4
ligands attached at the corners of a square
Coordination numbers range from 1 to 12, with 2, 4 and 6 being the most common. Linear and octahedral are the most common structures for coordination numbers 2 and 6, respectively.
|A Comparison of Linear and Octahedral Structures|
CN = 2
ligands and metal atom connected in a straight line
CN = 6
ligands attached at the corners of an octahedron