AMORPHOUS PRECURSORS FOR LOW-TEMPERATURE PREPARATION OF CHEVREL PHASES M(X)MO(6)S(8) AND THEIR TUNGSTEN ANALOGS

High-yield preparations of the amorphous ternary salts Na-2x(Mo6S8)Sx . yMeOH (with x = 1.0 to 1.5, y = 4 to 5) and Na-2.1 (W6S8)S-1.05. 5.4MeOH have been devised by reaction of M(6)Cl(12) (M = Mo or W) with NaSH and NaOBu in various ratios in refluxing n-BuOH for M = Mo and in refluxing MeCN for M = W. Characterization of these amorphous materials by chemical and spectroscopic methods (IR, Raman, PES) shows that the (M(6)S(8))(0) cluster units are present. Vacuum thermolysis of the amorphous Na-2x(Mo6S8)S-x . yMeOH first produces poorly crystalline NaMo6S8 by disproportionation at 800 degrees C and well-crystallized NaMo6S8 at greater than or equal to 900 degrees C. The amorphous tungsten compound disproportionates to W and WS2 at greater than or equal to 200 degrees C. Ion exchange of the sodium material in methanol with soluble M(2+) and M(3+) salts (M = Sn, Co, Ni, Pb, La, Ho) produces the M(2x/n)(n+)(Mo6S8)S-x . yMeOH compounds. For tungsten, only exchange with SnCl2 in THF was examined and resulted in Sn-x change with SnCl2 in THF was examined and resulted in Sn-x (W6S8)S-x . yMeOH. Conversion of Sn-x(Mo6S8)S-x . yMeOH to poorly crystalline Chevrel phase, SnMo6S8, was achieved by reduction under H-2 at 600 degrees C. Well-crystallized SnMo6S8 resulted at higher temperatures. Conversion of Sn-x(W6S8)S-x . yMeOH to SnW6S8 was not successful. (C) 1995 Academic Press, Inc.