Trinuclear Mo-Mo-Bonded Cluster Cation with One Oxygen Atom Cap and One Ethylidyne Cap

The compound [ 3(µ3-O) (#.3-CCH3) (O2CCH3)6(H2O)3] BF4-9H2O has been prepared and thoroughly characterized by a variety of physical measurements, including a complete X-ray crystallographic structure determination. It crystallizes in space group Pmn21 with Z = 2 and the following unit cell dimensions: a = 11.140 (1) Å, b = 7.939 (1) Å, c = 20.297 (3) Å, V = 1795.1 (7) Å3. The cation resides on the crystallographic mirror plane but has C3. symmetry within experimental error, with the following important mean distances: Mo-Mo, 2.752 (1) Å; -(µ3-0), 1.983 (4) Å; Mo-CCH3, 2.044 (7) Å; Mo-O(acetate), 2.12 (1) Å; Mo-0(H20), 2.164 (4) Å. The compound is diamagnetic and exhibits well-resolved and 13C NMR spectra completely consistent with the proposed structure. 13C tracer study shows that the ethylidyne group arises by reduction of the acetate group. The bonding in the trimolybdenum cluster can be described as three Mo-Mo bonds of order 1.