Sm₃S₃BO₃: The First Sulfide Borate without S–O and B–S Bonds

An unprecedented quaternary sulfide borate, Sm₃S₃BO₃ (1), was obtained via a high-temperature solid-state synthesis method. It crystallizes in the triclinic space group P1̅, and its 3D structure features a 2D (Sm₂S₂)_∞ wrinkled layer and a 1D (SmS)_∞ ladderlike chain bridged by trigonal-planar (BO₃)^3– through Sm–O bonds, demonstrating the first sulfide borate without S–O and B–S bonds. Its optical energy gap is measured to be around 2.5 eV and verified by electronic structure calculation.