A Complex Reaction Product of Dimolybdenum Tetraacetate with Aqueous Hydrochloric Acid. Structural Characterization of the Hydrido-Bridged [MO₂C1₈H]^3-Ion, the [MO(0)C1₄(H₂0)]- Ion, and an H₅O₂⁺Ion with an Exceptionally Short Hydrogen Bond

From a solution prepared by dissolving Mo₂(O₂CCH₃)₄in 12 M HCI and heating to 70°C in air followed by addition of tetraethylammonium chloride, deep yellow crystals of [(C₂H₅)₄N]₃(H₅O₂)[Mo₂Cl₈H][MoCl₄0(H₂0)] are slowly deposited. This compound was identified and fully characterized by X-ray crystallography. It contains three entities of structural interest. First, the diaquahydrogen ion, H₅O₂⁺, occurs here with an O-H-O distance shorter by ca. 0.07 Å than any previously reported in this ion; indeed, at 2.34 (1) Å, it is comparable to the few shortest O-H-O bonds known. Second, the [Mo₂Cl₈H]^3-ion, with a μ-H atom, is here found in an ordered condition and the hydrogen atom has been located and refined in one of the bridging positions; the Mo-H distances are 1.73 Å. Third, a full structural description of the [trans-MoCl₄O-(H₂O)]- ion is given. The Mo=O distance is 1.66 (1) Å while Mo-OH₂is 2.33 (1) Å. This remarkable compound forms or-thorhombic crystals, space group Pnma, with a = 26.785 (7) Å, b = 10.454 (2) Å, c = 16.874 (4) Å, V = 4725 (2) Å,³and Z = 4. Using 1868 reflections having l>3σ(1) the structure was refined to discrepancy indices of R₁= 0.046 and R₂= 0.064 and a goodness-of-fit index of 1.35.