Due to the similar aqueous chemistries of aluminium and iron, it has been long thought that an analogous iron polycation should be isolatable from water. Moreover, in 2007, the structure of ferrihydrite was determined and shown to be built of iron Keggin ions. This further captured scientists' imagination and drive to isolate the iron Keggin ion. In 2015, the iron Keggin ion was isolated from water, but as a polyanion with a −17 charge; and protecting chemistry was required. Iron-bound water is very acidic; so it is difficult to capture the intermediate Keggin ion form without bulky and nonprotic ligands instead of the water that is found in the aluminum Keggin ion. However, more important in this synthesis was the bismuth () counterions that provided high positive charge to stabilize the high negative charge of the heptadecavalent polyanion.