Syntheses, structures and electrochemistry of two complexes containing quadruply bonded dimolybdenum atoms

The syntheses, electrochemistry and structures of Mo2(O2CCH2-p-C6H4OH)4, (1·2THF), and Mo2(O2CC(OH)(C6H5)2)4, (2·4THF), as determined by single-crystal X-ray diffraction, are reported. Both molecules crystallized with two axially coordinated THF molecules and 2 contained two additional THF molecules hydrogen bonded to two of the OH groups on the benzilato ligands. Complex 1 crystallized in an extended geometric arrangement involving hydrogen bonds between layers of molecules. The MoMo distance in 1 at 2.0972(8) Å is shorter than that in 2 at 2.1044(10) Å. There was also a large difference in the oxidation potentials of these two compounds with 1 and 2 exhibiting E1/2 (ox) of 526 and 820 mV, respectively. These effects are attributed to differences in the electron donation ability in the ligands (p-hydroxy phenylacetic and benzilic acids) as assessed by their pKa values.