One of the largest real estate deals in Portland’s history closed this week, with the $66 million sale of One and Two Portland Square to a New York City investment group. North River Co., a New York City based commercial real estate development firm and an affiliate of Waterfront Maine, bought the two buildings and their parking lots which together cover 7 acres of downtown property, according to a release from CBRE | The Boulos Co., the real estate company that brokered the deal. “This particular property is significant not only because of its location, quality and size,” said Boulos’ Drew Sigfridson, who was the buyer’s adviser in the deal, in the release.