Ternary Molybdenum Sulfides of the Heavy Alkali Metals Monika Kümpers and Robert Schöllhorn* Anorganisch-Chemisches Institut Der Universität Münster

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Ternary Molybdenum Sulfides of the Heavy Alkali Metals Monika Kümpers and Robert Schöllhorn* Anorganisch-Chemisches Institut der Universität Münster,

Gievenbecker Weg 9, D-4400 Münster (pm)

Z. Naturforsch. 35b, 929-930 (1980); 442 received April, 1980 Ternary, Molybdenum Sulfides, 440 Molybdenum Disulfide 438 Two series of ternary molybdenum sulfides, 270 290 310 330 ASMO4S6 (A = K, Rb, Cs) and A2M015S20 d (pm) (A = K, Rb), were prepared by reduction of molybdenum disulfide with alkali metals in Fig. 1. Ternary alkali molybdenum sulfides Aa;Mo4S6: alkali halide melts at 1100-1300 K. All com- dependance of hexagonal lattice parameters on cation pounds are hexagonal and show electronic diameter d. conductivity; structural characteristics suggest isolated [Mo/S]^ chains as lattice elements for From Fig. 1 it can be seen that the a axis varies AzMo4S6. linearly with the cation diameter, while the c axis remains almost constant. This fact along with the observation of strongly anisometric crystal mor- Ternary molybdenum sulfides A^Mo^Sz with the phology, high elasticity and perfect cleavage of the oxidation state of molybdenum < + 6 are of actual crystals parallel to the hexagonal c axis suggests a interest with respect to their structural features and structure consisting of isolated rigid (Mo4Se)Sö one" their unusual physical properties [1-3]. Whereas dimensional matrix units held together by the alkali compounds with transition and post transition cations. All single crystals investigated so far elements have been studied rather thoroughly, the exhibited specific structure defects, however, and a information on ternary molybdenum sulfides with complete structure determination will have to wait strongly electropositive elements is much less satis- for crystals of better quality by improved growth factory. Metastable alkali phases AJMoSa with techniques. Preliminary studies on the physical layered structures [2, 4, 5] and AZMOÖSS with frame- properties of these phase indicate a rather high work structure [6] can be obtained at ~300 K via electronic conductivity which is likely to be due to chemical or electrochemical intercalation. Com- metal-metal bonding. pounds prepared at high temperatures have been Extended reaction times at 1300 K led to the described by several authors [7-9]; their detailed formation of additional molybdenum rich phases in structures are, however, unknown so far. We report KCl and RbCl melts which crystallize as compact here on the formation and characterization of two brittle grey needles with hexagonal cross section and new series of ternary molybdenum chalcogenides metallic lustre. The stoichiometry of the potassium w hich were obtained from alkali halide melts. compound (electron microprobe data using K2Pd3S4 The reduction of M0S2 with the corresponding as reference sample) was found to correspond to alkali metal in molybdenum autoclaves at 1100 to K0.4MO3S4. X-ray powder diagrams can be indexed 1300 K under argon atmosphere in KCl, RbCl and hexagonally; lattice parameters are given in Table I. CsCl melts results in the formation of whisker-like The density observed for Ko.3Mo3S4 is equivalent to grey needles with metallic appearance up to 5 mm q = 3.89 g/cm3; the calculated value amounts to in length. They are stable towards air and H2O and q = 4.11 g/cm3 with Z = 5, i.e. a stoichiometry of were isolated from the salt matrix by washing with K2M015S20 per unit cell. The rubidium phase was water; the analytical composition corresponds to found to be isomorphous with the potassium com- AZM02S3 with x ~ 1/3. X-ray powder diagrams and pound (Table I). Although symmetry and lattice single crystal Weissenberg photographs revealed that the three compounds are isomorphous with Table I. Hexagonal lattice parameters of alkali molyb- hexagonal symmetry and the space group P63/m; denum sulfides A*MO4S6 and A2MOISS2O- lattice parameters are given in Table I. The ex- perimental density observed for the Cs+ compound Ternary phase a [pm] c [pm] (x = 0.33) corresponds to £ = 3.49 g/cm3; the calculated density with Z — 2 amounts to q = 3.35 g/cm3. KsMo4S6 873.8 441.3 RbaMo4S6 895.9 441.2 CszMO4S6 928.8 441.0 * Reprint requests to Prof. Dr. R. Schöllhorn. K2M015S20 922.7 1181.0 0340-5087/80/0700-0929/$ 01.00/0 Rb2Moi5S2o 923.6 1174.1 930 Notizen. parameters suggest a structural similarity to the Table II. Orthorhombic lattice parameters of hydrated well-known ternary molybdenum sulfides TxMoeSs layered alkali molybdenum sulfides [1], intensity values and systematic extinctions do Aa:+(H20)2/[MoS2?-. not agree with this assumption. It is more likely A a [pm] b [pm] c [pm] that these sulfides are structurally related to In3Moi5Sei9 which shows both MoöSeg and MogSen Na 655.1 1137.2 2492.9 building blocks [10]. The minor quality of single K 648.4 1122.9 1842.3 crystals isolated so far prevented a complete X-ray Rb 648.7 1124.1 1875.7 structure analysis. With decreasing reaction temperature the ap- Cs 649.4 1125.3 1915.3 pearance of layered alkali molybdenum sulfides AxMoS2 is observed which exhibit a distorted M0S2 related layered binary and ternary dichalcogenides sublattice with considerable stacking disorder. As [3, 11]. described by us earlier these compounds easily According to electron diffraction and X-ray undergo topotactic solvation [9]. Electron diffrac- powder data the hydrogen bronze H0.3M0S2 [9] was tion studies on hydrated samples of improved found to exist in two modifications: (i) ortho- crystal quality now indicate that their symmetry is rhombic, a = 647 pm, b — 1120 pm, c = n • 599 pm not hexagonal as reported originally but ortho- (n = 1, 2, 3); (ii) hexagonal, a = 560 pm, c — rhombic (Table II) with the following correlation: n • 599 pm. Both phases show considerable stacking disorder. ao = 2 ay, bo = 2 an • YS; Co = cy

The orthorhombic distortion of the [MoS2]x_ sub- The authors are grateful to Dr. G. A. Wiegers, lattice is supposedly due to the formation of metal- Groningen, for discussions on defect structure prob- metal chains similar to those found for a series of lems.

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