INCOMPLETE CUBANES M₃X₄⁴⁺. Alan Hazell^a, Michael Brorson^b, Claus Jacobsen^b, Birgitte Jespersen^b and Iver Schmidt^{b a}Chemistry Dept. Aarhus University, DK-8000 Århus C, Denmark. ^bHaldor Topsøe A/S, Nymøllevej 55, DK-2800 Lyngby, Denmark.

Cluster compounds of the type M₃X₄⁴⁺ and M₃X₄M'⁴⁺ (M = Mo,W; X = O,S; M' = Co,Ni,Fe) are being studied as catalysts for homogeneous hydrosulphurization e.g.

C₄H₈S + 2H₂--> C₄H₁₀ + H₂S

The structures of two such compounds have been studied:

1 (NH₄)_4-xK_x[Mo₃O₄(CHOO)8*(H₃O)*(CHOO)*H₂O (x = 0.80) and

2 K₅[W₃S₄(CHOO)₉]*(CHOO)*3H₂O.

1 is triclinic, space group P-1 with a = 11.011(2), b = 13.310(2), c =9.993(1)Å, [[alpha]] = 106.817(7), [[beta]] = 91.651(9), [[gamma]]= 88.340(9)deg., Z = 2, R(F) = 0.026 for N_o = 3972 and N_v = 451. 2 is monoclinic, space group C2/m with a = 19.606(6), b = 14.348(7), c = 13.627(5)Å and [[beta]] = 118.94(2)deg., Z = 4, R(F) = 0.049 for N_o = 2656 and N_v = 226.

1 contains isolated [Mo(iv)₃O₄(CHOO)₈]^4- anions with one of the formate ions bridging two molybdenum atoms whereas in 2 all nine monodentate formate ions are bound to a W(iv)₃S₄ cluster. In both compounds there is a free formate ion. In 1 two of the cation sites are disordered and are occupied by either potassium or ammonium ions. 2 is either disordered or has a lower symmetry than C2/m, but refinement in lower symmetry space groups did not give a lower R-value.