Joymark Realty Trust has acquired two adjacent properties on Newbury St. in the city's Back Bay from The Mount Vernon Co. The retail/office building at 276 Newbury sold for $5.9 million. The four-story property totals 5,467 s/f and has street level retail space. The 10-unit multifamily property at 278 Newbury traded for $3.75 million. That property totals 4,912 s/f. Both buildings sold vacant. Joymark plans to knock down the adjoining walls and combine the properties to use as a corporate office. Both parties were self-represented in the deal.