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Anionic Halomolybdate(III) Chemistry. Tetrahydrofuran Loss from [MoX3Y(THF)2]- (X, Y = Cl, Br, I), Preparation and Properties of [Mo3X12]3- (X = Br, I), and Crystal Structure of the Edge-Sharing Trioctahedral [PPh4]3[Mo3I12]

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journal contribution
posted on 04.12.1996, 00:00 by James C. Fettinger, John C. Gordon, Sundeep P. Mattamana, Charles J. O'Connor, Rinaldo Poli, Ghadi Salem
By interaction of MoX3(THF)3 with [Cat]X in THF, the salts [Cat][MoX4(THF)2] have been synthesized [X = I, Cat = PPh4, NBu4, NPr4, (Ph3P)2N; X = Br, Cat = NBu4, PPh4 (Ph3P)2N]. Mixed-halide species [MoX3Y(THF)2]- (X, Y = Cl, Br, I) have also been generated in solution and investigated by 1H-NMR. When the tetraiodo, tetrabromo, and mixed bromoiodo salts are dissolved in CH2Cl2, clean loss of all coordinated THF is observed by 1H-NMR. On the other hand, [MoCl4(THF)2]- loses only 1.5 THF/Mo. The salts [Cat]3[Mo3X12] (X = Br, I) have been isolated from [Cat][MoX4(THF)2] or by running the reaction between MoX3(THF)3 and [Cat]X directly in CH2Cl2. The crystal structure of [PPh4]3[Mo3I12] exhibits a linear face-sharing trioctahedron for the trianion:  triclinic, space group P1̄; a = 11.385(2), b = 12.697(3), c = 16.849(2) Å; α = 76.65(2), β = 71.967(12), γ = 84.56(2)°; Z = 1; 431 parameters and 3957 data with I > 2σ(I). The metal−metal distance is 3.258(2) Å. Structural and magnetic data are consistent with the presence of a metal−metal σ 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 [Mo3X12]3- ions reacts with phosphines (PMe3, dppe) to form products of lower nuclearity by rupture of the bridging Mo−X bonds.