THE LAYERED COMPOSITE CRYSTAL-STRUCTURE OF THE TERNARY SULFIDE (BIS)(1.11)NBS2

Single crystals of a new mutually incommensurate composite crystal wit h layered structure, (BiS)(1.11)NbS2 were synthesized and the average substructures were studied by the single crystal X-ray diffraction met hod. The commensurate superlattice reflections along mutually incommen surate directions were observed for the BiS subsystem with the main di ffractions of the NbS2 subsystem. The NbS2 subsystem with a = 5.7504(9 ) Angstrom, b(1) = 3.3306(11) Angstrom, c = 23.0001(17) Angstrom, 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 subsy stem with a = 5.752(4) Angstrom, b(2) = 36.156(5) Angstrom, c = 23.001 (5) Angstrom, Z = 48, and space group F2mm has distorted two-atom-thic k double layers with an NaCl-type superstructure. The superstructure h as Bi-Bi bonds and nonbonded S-S pairs along mutually incommensurate d irections. The periodic length of b(2) is six times as large as those of simple NaCl-type arrangements. The Bi-Bi bonds are located in each half-length of b(2) in the BiS double layers. Each NbS2 sandwich and B iS double layer stack alternately to form a mutually incommensurate co mposite crystal with a layered structure. The structural relations amo ng (BiX)(x)TX(2) (T = Nb, Ta; X = S, Se) type compounds are also discu ssed. (C) 1995 Academic Press, Inc.