The five-coordinate Co(II) porphyrin, Co(1-Me-Im)(OEP), has been prepared and its structure determined from three-dimensional X-ray diffraction data. The complex crystallizes with four formula units in the monoclinic space group C2h5-P21/n with a = 14.049 (4) Å, b = 17.587 (8) Å, c = 14.331 (5) Å, and β = 95.20 (1)°. The cobalt atom is 0.16 (1) Å out of the mean plane of the porphyrin toward the imidazole ligand. The averaged Co-N(imidazole) and Co-N(porphyrin) bond lengths are 2.15 (1) and 1.96 (1) Å, respectively. The porphyrin itself is significantly nonplanar. Some of the β-C atoms of the ethyl groups are disordered. The structure suggests that the out-of-plane displacement of the cobalt atom in deoxycoboglobin is small compared with the displacement of the iron atom in hemoglobin and comparable with that in methemoglobin. In view of the fact that CoHb and met-Hb have differing quaternary structures, we conclude that structure of deoxy-CoHb is inconsistent with both the trigger mechanism of Perutz and the linear energy distribution model of Hopfield.
ASJC Scopus subject areas
- Colloid and Surface Chemistry