STRUCTURAL CHARACTERIZATION OF BI-NUCLEAR COBALT(III) AXIAL-METHYL ALCOHOL-HYDROCHLORIC ACID TETRAPHENYL-PORPHYRIN COMPLEX

Abstract

Simple modification(s) of the conventional preparation of Co(II)TPP led to a new cobalt complex. Structural investigation of the new complex was carried-out by using elemental analysis, physicochemical and spectroscopic techniques. (1) The EDXRF spectrum indicates the presence of Cl⁻ in 1 :1 ratio with the cobalt ion. (2) IR analysis indicates that; (i) No changes in the main aromatic moieties of the ligand H₂TPP after chelation. (ii) The cobalt-ion is sited in the porphyrin core. (iii) The oxygen of methyl alcohol is attached to a non-carbon atom. (iv) Cobalt-nitrogen bonds are coordinate bonds. (3) UV results show a Co(III) metal ion is significantly changed by the nature of the axial ligands with only one band at 1525 nm. The split Soret band at 1395 and 1411 nm without shoulders could ensure the axiality of H-ĉl and (H-O-Cĥ₃) as electron withdrawing ligands. (4) Measurement of the magnetic suscepti[bcirc]ility indicates that + 3 is the oxidation state of the central cobalt ion of the prepared complex. (5) TGA analysis ensured that one Co(III) ion is chelated with one TPP² -dianion to produce one mole of complex. (6) X-ray diffraction analysis reveals that the main porphyrin core is preserved. However, due to metallation, the length of the Co-Co bond in a binuclear structure, via lateral overlap of d_π-d _π orbitals to achieve back-donation, is estimated as (3.06–3.22 Å). (7) NMR spectra of both H₂TPP and the prepared complex ensured removal of NH protons with characteristic bonds for both phenolic and pyrrolic protons. Although, the rotar protons of H₃COH appear upfield, the hydrochloric acid proton is assigned downfield. The number of protons detected by NMR, is in agreement with that predicted by elemental analysis. The final structure of the synthesized complex is predicted according to the C, H and N analysis as C₄₅H₃₃N₄ OClCo in a binuclear form. The above analysis indicates that the binuclear structure is dominant in the solid phase; the charged structure is preferred in solution.

Key Words:

• Cobalt(III)
• Porphyrins
• suprabiotic catalyst
• binuclear