sentences:  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 (Bi3+) counterions that provided high positive charge to stabilize the high negative charge of the heptadecavalent polyanion.The stability of the Keggin structure allows the metals in the anion to be readily reduced.