The penthouse at 50 United Nations Plaza in Turtle Bay, after more than a decade on the market and significant price reductions, finally found a buyer. Initially listed for $70 million in 2013, the 9,700-square-foot duplex sold for just under $40 million, making it Manhattan’s top contract last week. The luxurious unit features four bedrooms, seven bathrooms, and a 33-foot swimming pool. The building, developed by Zeckendorf Development and Global Holdings, houses diplomats and politicians. The second priciest contract was a $14 million condo at 111 West 57th Street.