MOLYBDENUM(II) TRIFLUORO ACETATE DIMER

Abstract

Molybdenum(II) trifluoroacetate dimer, Mo₂(O₂CCF₃)₄, has been prepared by reaction of Mo₂(O₂CCH₃)₄ with a 10:1 mixture of CF₃COOH and (CF₃CO)₂O under nitrogen. An X-ray structure determination shows that the compound has the dinuclear, carboxylate-bridged configuration of essentially D_4h symmetry previously established for a number of other transition metal carboxylates. The Mo-Mo and average Mo-O distances of 2.090(4) and 2.06 (2) A are not significantly different from those found in molybdenum(II) acetate dimer [2.11(1) and 2.10(2) A]. The Mo-Mo stretching frequencies in the Raman spectrum are also similar for the two compounds: 406 cm⁻¹ for the acetate and 393 cm⁻¹ (389 in Et₂O soln.) for the trifluoroacetate. The mass spectrum of the trifluoroacetate shows a strong molecular-ion peak, and a fragmentation pattern characterized by successive net loss of CF₂CO₂ units. The infrared, Raman, electronic and mass spectra are discussed. The compound crystallizes in the triclinic space group P1 with unit-cell dimensions a = 8.392(8), b = 9.209(9), c = 5.568(5) A; α = 91.18(4), β = 100.561(7), γ = 89.670 (7) deg.; V = 423.0(8) A₃; ρ _obs = 2.528(5) g/cm³ for Z = 1; ρ _obs = 2.48(5) g/ml. The structure was determined from the intensities of 630 unique reflections collected with a counter diffractometer; it was solved by direct methods and refined by full matrix least squares to a conventional R = 0.093. and weighted R = 0.080. The molecule lies on an inversion center in the crystal. There is one intermolecular contact less than the sum of van der Waals radii: Mo-O = 2.72(1) A; Mo-Mo-O = 161.0(4)°.