(Updates after sale)
MADRID, April 18 (Reuters) - Spain's Santander said on Tuesday it had raised 750 million euros by selling perpetual bonds which are convertible into ordinary shares if the bank's capital cushion slips below a certain level.
Santander said earlier on Tuesday it aimed to sell bonds worth up to 2 billion euros ($2.1 billion) to institutional investors through an accelerated book-building process.
The euro zone's biggest bank by market value has been working on boosting its reserves of capital, partly to comply with tighter regulatory guidelines.
It said the bonds will pay a 6.75 percent coupon for the first five years after their issuance - in line with the price guidance a banker arranging the deal gave to Thomson Reuters IFR.
The bonds will convert into equity if the bank's Common Equity Tier 1 ratio - a closely-watched measure of balance sheet strength - drops below 5.125 percent. ($1 = 0.9395 euros) (Reporting by Paul Day; Additional reporting by Isla Binnie; Editing by Sonya Dowsett)