Reactions of main group homopolynuclear cations with transition-metal carbonyls. Stabilisation of µ-Se22+ and η3-Te32+ dicationic ligands and crystal structures of [Mo(Te3)(CO)4][SbF6]2 and [FeW(Se2)(CO)8][SbF6]2

Abstract

Two tetrahedrane-like clusters, [FeW(Se₂)(CO)₈][SbF₆]₂ and [Mo(Te₃)(CO)₄][SbF₆]₂, have been prepared by reaction of the metal carbonyls [Fe₂(CO)₉], [W(CO)₆], and [Mo(CO)₆] with the homonuclear cations Se₄²⁺ and Te₄²⁺. The compounds contain the entities Se₂²⁺ and Te₃²⁺ which are stabilised by the presence of metal carbonyl fragments. The selenium compound is monoclinic, a= 15.251(4), b= 12.267(3), c= 12.047(3)Å, β= 92.047(3)°, space group P2₁/c; the tellurium compound is orthorhombic, a= 15.177(5), b= 8.367(4), c= 14.590(4)Å, space group Pnma. The geometry of the two clusters, their formation, and bonding are described.