A 12-room duplex at 950 Fifth Avenue, a vertical bastion of billionaires with just seven residences and an infinitely selective co-op board, sold for $22 million and was the most expensive sale of the week, according to city records. The original asking price for No. 5/6 was $27.5 million, and last fall a deal for the apartment fell through, according to a broker who was not involved in the transaction. The monthly maintenance is $19,516, and a maid's room, No. 8, transferred with the residence. With opulent interiors designed by Mica Ertegun and Chessy Rayner of MAC II, the four-bedroom, five-and-a-half-bath apartment has 11-foot ceilings, ample Central Park views, parquet de Versailles floors, and retains its original handmade wrought-iron-and-gilt banister on the sweeping staircase that leads to the private bedroom quarters on the upper level, where there is also a small kitchen for nighttime convenience. The dramatic corner living room has a wood-burning fireplace and adjoins a cozy library that has a fireplace as well as a powder room and dry bar. The formal dining room, which has travertine floors and another marble fireplace, faces south. The eat-in kitchen was fully renovated with SieMatic cabinetry, marble countertops, a Garland range and a double oven, and its adjacent breakfast room overlooks the cityscape and the Carlyle Hotel. Besides its park views and a hidden fireplace, the corner master suite has two of everything - two bedrooms, two bathrooms, two walk-in closets. There are two additional guest bedrooms, both with en-suite baths. The building was designed by the renowned James E.R. Carpenter in 1926 and its power broker residents past and present include Mortimer Zuckerman, the uber-media and real estate mogul; Howard Schultz, the chief executive of Starbucks; L. Dennis Kozlowski, the disgraced former head of Tyco; and Robert Hurst, the former president of the Whitney Museum. Mr. Zuckerman presides from the penthouse, and all seven residents sit on the board. The sellers, Jerome and Joan Serchuck, were represented by Cindy Kurtin and Jessica Vertullo Maher of Stribling & Associates. The new buyer opted for anonymity through a limited liability company, JIE Trust. Big Ticket includes closed sales from the previous week, ending Wednesday.