The ownership of downtown Boston’s 711 Atlantic Ave. building has been restructured in a deal that has a group led by Brian Donaghy, president of contractor Structure Tone, taking control and assuming the $12.8m mortgage on the property. Structure Tone, which manages big-ticket remodeling projects inside skyscrapers throughout the country, already is a tenant inside the building. Donaghy’s Structure Tone Equities assumed the mortgage as part of a $17.8m sale agreement, according to the Suffolk County Registry of Deeds. The former owner was Lexham Atlantic of Connecticut. The principal of that entity was Marc K. Lewis, managing member of Lexham Private Investors, a commercial real estate firm.