Is Citibank justified in sueing Wachovia?

Citibank has sued Wachovia for $ 60 bn. In the first place, are they justified in sueing Wachovia? If they are, is $ 60 bn. justified in a deal of $ 2 bn.? Moreover, the deal was yeat to be ped by the stockholders of Wachovia. Without it being ped, how can it have any legal effect?