NEW YORK CITY — California-based investment firm Avanath Capital Management has purchased 7 Dekalb, a 251-unit apartment building in Brooklyn, for $101.2 million. The 18-story building, which features mix of market-rate and affordable housing units, is located within the City Point mixed-use development. Amenities include a fitness center, rooftop deck, children’s play area, tenant lounge and a cinema room. Newmark represented the seller, The Brodsky Organization, in the transaction. Avanath plans to introduce new social services programs for residents, including afterschool care, professional development workshops and health classes.