Citigroup, the second biggest banking group in the US, is to receive a $7.5 billion injection from the Abu Dhabi government in a deal to strengthen its capital base in the face of the US housing slump and related credit squeeze. Citi said it had agreed to sell the Abu Dhabi Investment Authority $7.5 billion worth of "equity units", with mandatory conversion into common shares, swelling the ADIA's total holding in Citigroup to 4.9 per cent. "This investment, from one of the world's leading and most sophisticated equity investors, provides further capital to allow Citi to pursue attractive opportunities to grow its business," said Win Bischoff, Citigroup's acting chief executive in a statement. "This investment also enables us to access capital in an efficient manner, and is consistent with our strategy of maintaining a balance sheet that benefits from highly diverse sources of funding in terms of both geography and type of security," he added. ADIA displaces Saudi Prince Alwaleed bin Talal as Citi's largest shareholder. It has agreed to limit its holding to no more than 4.9 per cent, and it will not receive special rights of ownership or control, the banking group said in its statement. Earlier this month Citigroup revealed it was facing likely investment write-offs of between $8 to $11 billion, mostly related to losses in the sub-prime mortgage market. Charles Prince, the chairman and chief executive, resigned after reporting a 57 per cent drop in quarterly profits.