Putting the Bite on Metals - Chelation

Free and coordinated ammonia and water molecules. The second lone pair of water is oriented in a direction prohibiting its interaction with the same metal centre as the first. However, it does have the potential, in principle, to use this lone pair to bind to a second metal centre in a bridging coordination mode. (Other groups bound to the metals are left off to simplify the views.) 

Diaminomethane, a molecule with two amine groups. Once the first is coordinated, the second lone pair from the other amine can be oriented in a direction more appropriate for bonding than is the case for two lone pairs on a single atom, with limited bond angle distortion permitting both to coordinate, illustrated at right, in a chelated coordination mode. 

Metal ion binding options for a carboxylate group, featuring various monodentate and didentate coordination modes. 

O returning us to the M, so four atoms are involved in the continuous ring, meaning it is a four-membered chelate ring. 

The stepwise process for chelation of diaminoethane. This features initial monodentate formation, rearrangement and orientation of the second lone pair, and its subsequent binding to form the chelate ring. s 

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