Citigroup (C) shares closed at $4.06 Thursday. But the United Arab Emirates will soon buy $7.5 billion in shares of the company -- for $31.83 each.

That's gotta hurt. The lesson here? Don't ink any deals right before the financial world falls off a cliff.

The UAE thought it was getting a great score in November 2007, according to The Wall Street Journal. Citigroup was in serious money trouble, and the Abu Dhabi Investment Authority (the UAE's sovereign fund) came to the rescue with a $7.5 billion check.

In return, Abu Dhabi agreed to receive an 11% annual dividend for about two years. After that, it would get its investment back in the form of Citigroup stock.

The fatal mistake here was that Abu Dhabi agreed to a stock price of $31.83. That was close to Citigroup's stock price back then, and Abu Dhabi likely figured that shares would grow in value. If that happened, $31.83 looked like a great deal.

"This investment reflects our confidence in Citi's potential to build shareholder value," Abu Dhabi's managing director said at the time, according to the Journal.

So, unless Citigroup shares make a remarkable turnaround, the bank stands to sell its stock to Abu Dhabi at seven times the market price, the Journal reports.