ISOLATION, X-RAY CRYSTAL-STRUCTURE AND CO-59 NUCLEAR-MAGNETIC-RESONANCE SPECTRAL INVESTIGATION OF THE PARTIALLY NITRATED COBALT(III) ACETYLACETONATO COMPLEX [CO(ACAC)2(NO2ACAC)]

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 P1BAR, with a 7.651(1), b 8-353(1), c 14.557(2) angstrom, alpha-78.98(1), beta-83-71(2), gamma-75.32 (1)-degrees and Z 2. The structure refined to a final R value of 0 - 074 for 2287 'observed' [I > 3-sigma(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 50.7-degrees 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 Co-59 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 the gamma-carbon atom of the acetylacetonato chelate ring. The Co-59 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).