Synthesis and structure of 3,5-dimethylpyrazolyl iron and cobalt dinitrosyl dimers

Abstract

The synthesis and characterization of two 3,5-dimethylpyrazolyl metal dinitrosyl dimers [(N2C5H7)M(NO)2]2 (where M = Fe or Co) are described and their X-ray crystal structures detailed. Both complexes crystallize in the monoclinic space group C2/c, a = 23.848(2), 23.722(4), b = 10.7775(7), 10.6888(6), c = 14.764(1), 14.712(2) Å, β = 117.366(6), 117.094(7)°, Z = 8 (for the iron and cobalt complexes respectively). The structure of the iron complex was solved by Patterson and Fourier syntheses. The cobalt complex is isomorphous with the iron analog. Both structures were refined by full-matrix least-squares procedures to R = 0.028 and 0.035 for 4251 and 3376 reflections with I ≥ 3σ(I) respectively. Both complexes adopt a boat conformation for the central M—(N—N)2—M ring and display significantly non-linear M—N—O groups. The coordination geometry about the metal atoms is distorted tetrahedral. Important molecular dimensions (distances corrected for libration) are: mean Fe—N(pyrazolyl), 2.009(5), mean Fe—NO, 1.696(2) Å, Fe—N—O, 158.5(3)–168.2(2)°, mean Co—N(pyrazolyl), 1.992(7), Co—NO, 1.646(3)–1.680(3) Å, and Co—N—O, 161.6(3)–173.5(3)°. The iron complex is paramagnetic with formally "17-electron" iron atoms. Both structures are compared with similar four-coordinate metal dinitrosyl compounds.