The Layered Composite Crystal Structure of the Ternary Sulfide (BiS)1.11NbS2

Abstract

Single crystals of a new mutually incommensurate composite crystal with layered structure, (BiS)1.11NbS2 were synthesized and the average substructures were studied by the single crystal X-ray diffraction method. The commensurate superlattice reflections along mutually incommensurate directions were observed for the BiS subsystem with the main diffractions of the NbS2 subsystem. The NbS2 subsystem with a = 5.7504(9) Å, b1 = 3.3306(11) Å, c = 23,0001(17) Å, Z = 4, and space group F2mm takes the form of 2H-type NbS2 sandwiches with Nb atoms trigonal-prismatically coordinated by S atoms. The BiS subsystem with a = 5.752(4) Å, b2 = 36.156(5) Å, c = 23.001(5) Å, Z = 48, and space group F2mm has distorted two-atom-thick double layers with an NaCl-type superstructure. The superstructure has Bi-Bi bonds and non-bonded S-S pairs along mutually incommensurate directions. The periodic length of b2 is six times as large as those of simple NaCl-type arrangements. The Bi-Bi bonds are located in each half-length of b2 in the BiS double layers. Each NbS2 sandwich and BiS double layer stack alternately to form a mutually incommensurate composite crystal with a layered structure. The structural relations among (BiX)xTX2 (T = Nb, Ta; X = S, Se) type compounds are also discussed.