EXAFS STUDIES OF MOLECULAR GEOMETRIES OF SOME CO-II AND CO-III PORPHYRINS

Co K-edge EXAFS data of some (porphinato)cobalt(III) complexes with am ine ligands in chloroform solution are reported. Data for the followin g compounds were collected: chloro(tetraphenylporphinato)cobalt(III)) (TPPCoCl) complexed with pyridine (A), isoquinoline (B) and cyclohexyl amine (C) and 4-methylpiperidine complexed with the sterically hindere d hloro(tetra-o-dichlorophenylporphinato)cobalt(III) (TClPCoCl) (D) an d hloro(tetra-o-difluorophenylporphinato)cobalt(III) (TFPCoCl) (E). In addition to the four N atoms from the macrocyclic porphyrin ligand, t he cobalt atom is coordinated to either one amine and a chlorine atom (A and B) or two axial amine ligands with the chloride as a counterion (C-E). An interesting feature is the longer Co-Cl distances in A and B relative to those in the solid state. The Co-N distances are represe nted by a single composite distance ranging from 1.91(1) to 1.95(1) An gstrom. The Co-N bond lengths for the ortho-substituted porphyrins wer e found to be similar to those in the less hindered TPP complexes. The EXAFS for the cobalt(II) compounds TClPCo (F) and TFPCo (G) gave dist ances similar to those of the crystal structure of TPPCo. The equatori al Co-N distances depend more on the conformation of the porphyrin cor e than on the cobalt oxidation state, as demonstrated by the similarit y between the Co-III-N and Co-II-N distances.