Density functional theory calculations involving various transition metal porphyrin complexes and their oxygen adducts

• Main Author: Quevada, Nikko P.
• Format: text
• Published: Animo Repository 2009
• Subjects: Density functionals; Porphyrins; Chemistry
• Online Access: https://animorepository.dlsu.edu.ph/faculty_research/13138
• Institution: De La Salle University

We conducted a theoretical investigation of the geometric, vibrational, and electronic structures of seven transition metal porphyrins and their oxygen adducts using Density Functional Theory (DFT). The values of various geometric parameters that we calculated agree reasonably well with the experiment and calculated values previously reported by various groups. No significant change in the porphyrin geometry was observed whether or not its core contains a metal atom. In general, the porphyrin moiety itself remains planar regardless of the type of metal center. The metalloporphyrins exhibit an unexpected charge distribution in that, considering the apparent symmetry of the porphyrin complexes, not every atom type has the same charge: one carbon atom in the ring may be negatively-charged while another is positively-charged. However, each pair of carbons, nitrogens, and hydrogen atoms on opposite sides of the porphyrin ring have the sam change in the metal center from left to right in the fourth row of the periodic table regardless of the spin state of the metal atom. The total energy also becomes more negative as one goes up the column (from Os to Ru to Fe) in the periodic table for both the singlet and triplet states. Both Mn (quartet) and Fe (triplet) porphyrins are found to contribute to both the HOMO and LUMO. In contrast to Tsuda et al.'s results, the Co d electrons contribute to both the HOMO and LUMO. Also, not only do both Co and Fe contribute to the LUMO, but their HOMOs are both purely metallic in character. Among the seven metalloporphyrins, Ni(singlet)-Por imparts no metal d electron contribution to the HOMO, while Co (quartet), Ni (triplet), and Ru (singlet) have very little metal d electron contribution to the HOMO. These metal porphyrins are thus expected to be relatively weaker catalysts than, say, the Mn(II)Por and Fe(II)Por metal porphyrins. In contrast, each metal center in Cr(II)Por, Mn(II)Por, Fe(II)Por, and Os(II)Por contributes d electrons to both the LUMO and HOMO, suggesting good catalytic potential in oxygen reductions for these metalloporphyrins.