Isolation, X-Ray Crystal Structure and ⁵⁹Co Nuclear Magnetic Resonance Spectral Investigation of the Partially Nitrated Cobalt(III) Acetylacetonato Complex [Co(acac)₂(NO₂acac)]

Abstract

The complex [Co( acac )₂(NO₂acac)] has been isolated after fractional crystallization from a reaction mixture of [Co( acac )₃] and nitrating agent. The complex crystallizes in the triclinic space group P1, with c 14.557(2) Å , α 78.98(1), β 83.71(2), γ75.32(1)° and Z 2. The structure refined to a final R value of 0.074 for 2287 'observed' [I > 3 σ(I)] reflections. The structure consists of discrete complex molecules with the cobalt atom surrounded by six oxygen atoms at the corners of a distorted octahedron. The NO₂ group is twisted at 50.7º to the chelate ring on which it is situated and has little influence on the geometry, with intrachelate and interchelate oxygen-oxygen separations essentially the same as those found in [Co( acac )₃]. The ⁵⁹Co n.m.r. spectra of the [Co( acac )₂(NO₂acac)] complex, as well as [Co( acac )₃], [Co(NO₂acac)₃] and [Co( acac )(NO₂acac)₂], have been recorded, this resonance being particularly sensitive to substitution on they γcarbon atom of the acetylacetonato chelate ring. The ⁵⁹CO relaxation rates for the [Co( acac )₂(NO₂acac)] and [Co( acac )(NO₂acac)₂] complexes are faster than that displayed by the symmetric [Co(NO₂acac)₃] complex, (1948 ± 20, 2765 ± 30 and 1696 ± 20 s^-1, respectively). The results obtained for the relaxation rates for these complexes are compared with those obtained for similar halide-substituted complexes [Co( acac )₃-_n( Xacac )_n]   (X = Cl , Br, I; n = 0-3).