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Introduction. Several modifications [see Hulliger (1976) for a review] are known for tantalum disulfide, the forms extensively studied being 1T-TaS2, space group P3ml [Cd(OH)2-type structure], with Ta in octahedral coordination by S, and 2H-TaS2, space

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Single-crystal X-ray data of the mixed layer compound La32Nb28S88 reported by Meerschaut, Rabu & Rouxel [Jr. Solid State Chem. (1989), 78, 35-45] in an orthorhombic supercell, a=23.216, b = 5.806, c= 23.031 ,A,, space group Bbcb, were analyzed in terms of a composite crystal (LaS)~.~4NbS2, consisting of an LaS part with a=5. 325with Nb in trigonal prisms of S atoms (as in 2H-NbS2). NbS2 sandwiches lc apart are displaced with respect to each other by over ½b. The composition of the compounds is determined by the ratio a/a" and the number of formula units per unit cell of the two sublattices. The symmetry of the complete structure, including the effect of the mutual modulation, is analyzed in terms of a four-dimensional superspace group.

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SnS),,,TiS, is a misfit layer compound built of alternately double layers of SnS with distorted rocksalt-type structure and sandwiches of Tis2 slightly distorted compared with those of 1T-TiS2. For comparison with other misfit layer compounds the triclinic subsystems are described in centred unit cells: for the SnS part, a, = 5.683( 1) A, b , =5.832( 1)A, c , = 11.680(5) A, LY, = 95.85(3)", p , = 94.78(33", y , = 90.03(2)', the space group is C i and Z = 4; for the TisI part. a2 = 3.412(1) A, b2 = 5.835(1) A. cz = 23.289(3) A, n2 = 95.86(1)",~2=90.30(1)',~i=90.01(1)0,thespacegroupis~andZ=4.Inrealspace,o, and a2 as well as b , and b2 are parallel while the c axe3 diverge. In reciprocal space both sublattices have the (b'. c') plane in common. Refinements were performed of the SnS part using 1351 independent reflections (Rr= 0.087) and of the Tis2 part using 714 reflections (RF = 0,080). Each Sn atom is coordinated to five S atoms ofthe SnS double layer with SnS distancesof2.610(3), 2.864(4),2.873(4).2.911(4) and2.976(4) A, and at largerdistances to S of Tisi. The Ti-S distances of the distorted Tis, octahedra with symmetry i are 2.417(2), 2.429(1) and 2.428(1) A. Sn atoms are between rows of sulphur along a of S of Tis?. The structural relationship with other misfit layer compounds is discussed.