Ligand Analogy

Constructing a Ligand is a lot like building a vehicle.  Each vehicle has a particular purpose.  If you want to go fast, you build a racecar.  If you want to carry a lot of stuff, you build a dump truck.  If you want to knock something over, you build a bulldozer.  If you want to fly, you build an airplane.  If you want to go underwater, you build a submarine. 

Yet, none of those vehicles can do what they are designed to do without a driver/pilot.  This is similar to the relationship between a ligand and a metal ion.  We spend a lot of time and effort designing ligands to have certain properties.  But, much like a car without a driver, the ligand is not going to be able to do its job without the metal ion.  So, designing and synthesizing a ligand is much like designing and building a car.  The ligand can’t do its ultimate job until the metal takes its place in the “driver’s seat”. 

In addition, not any old driver will do.  If you want your airplane to fly to the best of its designed abilities, not any old pilot will do; you need a top gun.  For your racecar to win the Indianapolis 500, someone off the street isn’t going to do it.  You need a professional driver.  The same is true for ligands.  You can put lots of different metals into most ligands.  Yet, only one or two will give the maximum performance for any one job.  Interestingly, some ligands will be very good at one job (reaction) with one metal ion, but can be very good at another reaction with a different metal ion.