Na6Si3S8O: the first example of a sulfide silicate exhibiting unusual tri-polymerized [Si3S8O]6− units without S–O bonds

Abstract

Generally, sulfur is inclined to combine with oxygen to form sulfate ions in a solid-state reaction. Interestingly, an extraordinary sulfide silicate, Na₆Si₃S₈O, was successfully obtained in a vacuum-sealed silica tube for the first time. Its crystal structure features novel 1D straight chains formed by the interconnection of tri-polymerized [Si₃S₈O]⁶⁻ and [Na₄S₅O]¹¹⁻ units, demonstrating the first sulfide silicate exhibiting S–Na–O and S–Si–O connections without S–O bonds. Moreover, Na₆Si₃S₈O is also verified as a promising birefringent material owing to its large birefringence (Δn = 0.215–0.094 from 0.3 to 4.0 μm).