Changing the size of the incoming ligand in a coordination complex can significantly affect the rate of substitution. This effect is closely related to the steric hindrance of the complex.Steric hindrance refers to the spatial constraints that arise due to the size and shape of molecules, which can limit their reactivity. In the context of a coordination complex, steric hindrance can affect the ability of an incoming ligand to approach and interact with the central metal ion.When the size of the incoming ligand increases, the steric hindrance also increases. This can lead to a decrease in the rate of substitution, as the larger ligand may have more difficulty approaching and interacting with the central metal ion. The increased steric hindrance can also cause the reaction pathway to change, potentially leading to different products or reaction mechanisms.Conversely, if the size of the incoming ligand decreases, the steric hindrance will decrease, potentially leading to an increase in the rate of substitution. Smaller ligands can more easily approach and interact with the central metal ion, allowing for faster substitution reactions.In summary, the size of the incoming ligand can significantly impact the rate of substitution in a coordination complex due to its effect on steric hindrance. Larger ligands generally lead to increased steric hindrance and slower substitution reactions, while smaller ligands can result in decreased steric hindrance and faster reactions.