Preparation of the Oxotetrabromo-and Oxotetraiodomolybdenum (V) Ions from Dimolybdenum Tetraacetate. Structures by X-ray Crystallography

The [M0OBr₄(H²O)]-ion has long been known, but its structure has been determined only roughly. We have found that a number of compounds containing this ion are formed when Mo2(O2CCH3)4 reacts in the presence of oxygen with aqueous HBΔ. These preparative reactions are reported in detail and the crystal structures of two compounds, one of which contains two crystallographically independent [MoOBr4(H2O)] ions, reported. The structurally characterized compounds and their crystallographic properties are as follows. 1, (C5H5NH)5[MoOBr4(H2O)]3Br2: space group Pmma; a=21.875 (3), b=8.487 (1), c=13.724 (2) υ; V=2547.9 (1) υ3; the unit cell contains six [M0OBr₄(H²O)]-ions, four with m symmetry and two with mm symmetry. 2, (Et4N)[MoOBr4(H2O)]: space group Pnma; a=11.202 (2), b= 12.957 (3), c=11.523 (2) υ; V=1672.5 (1) υ3; Z=4. The compound (Et4N)[M0OI4(H2O)] (3), the first reported compound containing the oxoiodo ion, is prepared in a similar way. It is isomorphous with 2 with a = 11.592 (3) υ, b=13.623 (3) υ, c=11.898 (3) υ, and V= 1879 (1) υ3. The Mo=O distances in 1 are 1.61 (2) and 1.62 (2) υ, while those in 2 and 3 are 1.65 (1) and 1.65 (1) υ.