Chicago’s gentrifying River North neighborhood is a gritty mix of older commercial and newer residential buildings. Among these is 747 North Clark Street, a 22,000-square-foot condominium completed last year. The seven-story structure fills a midblock lot only 40 feet wide by 100 feet deep, with its lot-line walls, flanked by buildings of only two stories, mostly blank. But its facade is an eye-catcher: glass in a black-steel frame whose elegant proportions recall Mies van der Rohe’s archetypal Lake Shore Drive apartment towers. It pays fitting homage to Chicago’s modernist heritage.