The preparation,structure and spectra properties of dual μ3-oxo bridged tetranuclear complexes containing the (CrFe4-nO2]8+ core (n =0, 2, 4)

The preparation and characterization of Cr_nFe_4-nO₂(O₂CMe)₇(bipy)₂]Cl (1, n=0; 2, n=2; 3, n=4, bipy=2,2'-bipyridine) are described. The three complexes (1, 2 and 3) are obtained by bipyridine-mediated conversion of trinuclear Cr_nFe_3-nO(O₂CMe)₆(H₂O)₃]⁺(1, n=0; 2, n=1; 3, n=3), and crystallized as three of approximate isomorphs. Crystal 2 is monoclinic with space group C2/c, a=27.454(5)Å, b=11.789(1)Å, c=16.570(3)Å, β=118.78(1)°, V=4700.8ų, z=4, μ(MoK)=11.64cm^?1, F(000)=2056, final R=0.058 and R_w=0.066 for 3479 reflections with I ? 3σ(I). The Fe and Cr atoms in the cation are all +3 oxide state and disordered in the lattice, which is also supported by its Mossbauer studies. The Cr₂Fe₂O₂]⁸⁺ core can be thought of as being derived from two edge-sharing M₃O units (M=Fe or Cr), and as a butterfly-like structure. The cations' structure of all three crystals are similar to each other and have C₂ symmetry. The species are characterized by IR spectra and magnetic techniques, with particular emphasis on differentiation of coordination bond strengths and electronic environment of metal atoms in these complexes.