  A quaternary compound Bi3O2S2Cl, which consists of novel [BiS2Cl]2-layers, is
reported. It adopts a layered structure of the space group I4/mmm (No. 139)
with lattice parameters: a = 3.927(1) {\AA}, c = 21.720(5) {\AA}. In this
compound, bismuth and chlorine atoms form an infinite planar layer, which is
unique among the bismuth halides. Superconductivity is observed in both
polycrystals and single crystals, and is significantly enhanced in the samples
prepared with less sulfur or at higher temperatures. By tuning the content of
sulfur, Bi3O2S2Cl can be converted from a semiconductor into a superconductor.
The superconducting critical temperature ranges from 2.6 K to 3.5 K. Our
discovery of the [BiS2Cl]2- layer opens another door in searching for the
bismuth compounds with novel physical properties.
