By interaction of MoX(3)(THF)(3) with [Cat]X in THF, the salts [Cat][MoX(4)(THF)(2)] have been synthesized [X = I, Cat = PPh(4), NBu(4), NPr4, (Ph(3)P)(2)N; X = Br, Cat = NBu(4), PPh(4)(Ph(3)P)(2)N]. Mixed-halide species [MoX(3)Y(THF)(2)](-), Y = Cl, Br, I) have also been generated in solution and investigated by H-1-NMR. When the tetraiodo, tetrabromo, and mixed bromoiodo salts are dissolved in CH2Cl2, clean loss of all coordinated THF is observed by H-1-NMR. On the other hand, [MoCl4(THF)(2)](-) loses only 1.5 THF/Mo. The salts [Cat](3)[Mo(3)X(12)] (X = Br, I) have been isolated from [Cat][MoX(4)(THF)(2)] or by running the reaction between MoX(3)(THF)(3) and [Cat]X directly in CH2Cl2. The crystal structure of [PPh(4)](3)[MO(3)I(12)] exhibits a linear face-sharing trioctahedron for the trianion : triclinic, space group P (1) over bar; a = 11.385(2), b = 12.697(3), c = 16.849(2) Angstrom; alpha = 76.65(2), beta = 71.967-(12), gamma = 84.56(2)degrees; Z = 1; 431 parameters and 3957 data with I > 2 sigma(I). The metal-metal distance is 3.258(2) Angstrom. Structural and magnetic data are consistent with the presence of a metal-metal sigma bond order of 1/2 and with the remaining 7 electrons being located in 7 substantially nonbonding orbitals, The ground state of the molecule is predicted to be subject to a Jahn-Teller distortion, which is experimentally apparent from the nature of the thermal ellipsoid of the central Mo atom. The [Mo(3)X(12)](3-) ions reacts with phosphines (PMe(3), dppe) to form products of lower nuclearity by rupture of the bridging Mo-X bonds.