Molybdenum(II) acetate explained

Molybdenum(II) acetate is a coordination compound with the formula Mo₂(O₂CCH₃)₄. It is a yellow, diamagnetic, air-stable solid that is slightly soluble in organic solvents. Molybdenum(II) acetate is an iconic example of a compound with a metal-metal quadruple bond.^[1]

Structure

Like several other transition metal carboxylate complexes, Mo₂(O₂CCH₃)₄ adopts a Chinese lantern structure.^[2] Each Mo(II) center in Mo₂(O₂CCH₃)₄ has four d valence electrons. These eight d-electrons form one σ, two π bonds, and one δ bond, creating a bonding electron configuration of σ²π⁴δ². Each of these bonds are formed by the overlapping of pairs of d orbitals.^[3] The four acetate groups bridge the two metal centers. The Mo-O bond between each Mo(II) center and O atom from acetate has a distance of 2.119 Å, and the Mo-Mo distance between the two metal centers is 2.0934 Å.

Preparation

Mo₂(O₂CCH₃)₄ is prepared by treating molybdenum hexacarbonyl (Mo(CO)₆) with acetic acid. The process strips CO ligands from the hexacarbonyl and results in the oxidation of Mo(0) to Mo(II).^{[4] [5]}

2 Mo(CO)₆ + 4 HO₂CCH₃ → Mo₂(O₂CCH₃)₄ + 12 CO + 2 H₂Trinuclear clusters are byproducts.^[6]

The reaction of HO₂CCH₃ and Mo(CO)₆ was first investigated by Bannister et al. in 1960. At the time, quadruple metal-metal bonds had not yet been discovered, so these authors proposed that Mo(O₂CCH₃)₂ was tetrahedral.^{[7] [8]} This perspective changed with Mason's characterization.^[9]

Applications

Mo₂(O₂CCH₃)₄ is generally used as an intermediate compound in a process to form other quadruply bonded molybdenum compounds. The acetate ligands can be replaced to give new compounds such as [Mo₂Cl₈]⁴⁻ and Mo₂Cl₄[P(C₄H₉)₃]₄.^{[10] [11]}

Notes and References

1. Girolami, G. S.; Rauchfuss, T. B. and Angelici, R. J., "Synthesis and Technique in Inorganic Chemistry third edition", University Science Books: Mill Valley, CA, 1999,
2. Cotton, F. A.; Hillard, E.A.; Murillo, C. A.; Zhou, H.-C. "After 155 Years, A Crystalline Chromium Carboxylate with a Supershort Cr-Cr Bond" J. Am. Chem. Soc., 2000, 122, 416-417. .
3. Blaudeau, J. P.; Pitzer, R. M. “ Ab Initio Studies of Ligand Effects on the Metal-Metal Bond in Dimolybdenum Complexes” J.Phys. Chem. 1994, vol. 98, pp. 4575-4579.
4. Brignole, A.G.; Cotton, F.A., “Rhenium and Molybdenum compounds containing quadruple compounds” Inorg. Synth. 1972, volume 13, pp. 81-89.
5. Pence, L. E.; Weisgerber, A. M.; Maounis, F.A.; “Synthesis of Molybdenum-Molybdenum Quadruple Bonds” J. Chem. Educ., 1999, vol. 76, 404-405.
6. Bino, A.; Cotton, F.A.; Dori, A.; J. Am. Chem. Soc. 1981, vol. 103, pp. 243-244. “A Aqueous New Chemistry of Organometallic, Trinuclear Cluster Compounds of Molybdenum”.
7. Bannister, E.; Wikinson, G. “Molybdenum(II) carboxylates” Chem. Ind. 1960, 319.
8. Stephenson, T.A.; Bannister, E.; Wilkinson, G. “Molybdenum(II) Carboxylates” J. Chem. Soc., 1964, pp. 2538.
9. D. Lawton, R. Mason "The Molecular Structure of Molybdenum(II) Acetate"J. Am. Chem. Soc. 1965, vol 87, pp 921–922.
10. Tsai, Y.C.; Chen H.Z.; Chang, C.C.; Yu, J.K.; Lee, G.H.; Wang, Y.; Kuo, T.S. “Journey from Mo-Mo Quadruple Bonds to Quintuple Bonds” J. Am. Chem. Soc., 2009, 131, 12534-12535.
11. Handa, M.; Mikuriya, M.; Kotera, T.; Yamada, K.; Nakso, T.; Matsumoto, H.; Kasuga, K. “Linear Chain Compounds of Molybdenum(II) Acetate Linked by Pyazine, 4,4’-Bipyridine, and 1,4- Diazabicyclo[2.2.2]octane” Bull. Chem. Soc. Jpn., 1995,68, 2567-2572.