Complex sentence: During their first 50 years, the Seven Buildings were some of the most fashionable addresses in the city, hosting congressmembers, cabinet officers, admirals, generals and diplomats, but by the 1890s, they were being used as commercial structures rather than homes.
Split into simpler sentences: During their first 50 years, the Seven Buildings were some of the most fashionable addresses in the city. But by the 1890s, they were being used as commercial structures rather than homes.