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Issue 42, 2007
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Molecular magnetic properties of heteroporphyrins: a theoretical analysis

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B3LYP/6-31G(d) optimization of porphyrin, tetraphenylporphyrin and their 21,23-diheteroatom substituted derivatives with O, S, and Se heteroatoms was performed. A planar macrocycle was found in all cases except 21,23-dioxatetraphenylporphyrin which presents only slight deviations from planarity. A Bader analysis uncovers the presence of S–S and Se–Se interactions in the four corresponding heteroporphyrins, which appreciably distort the original unsubstituted macrocycles. In the minimum energy structures of heterotetraphenylporphyrins the four meso phenyl groups slant alternatively to right or left so that the two pairs of opposite phenyls present a staggered conformation. The π current induced by a perpendicular magnetic field in porphyrin bifurcates across both types of pyrrole subunits but the presence of O, S and Se heteroatoms in 21,23-diheteroporphyrins causes a diminution of the current density through the inner section of the two heterorings and, consequently, the current path goes then through the outer section of these rings. The NICS values at the ring critical points of the heterorings are much larger (in absolute value) than those at the pyrrole ring critical points but appreciably smaller than that at the ring critical point of a pyrrole molecule. In agreement with experimental data the 1H NMR present appreciable downfield shifts for the β H atoms of the heterorings in the 21,23-heterosubstituted molecules.

Graphical abstract: Molecular magnetic properties of heteroporphyrins: a theoretical analysis

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The article was received on 18 Jun 2007, accepted on 24 Aug 2007 and first published on 07 Sep 2007

Article type: Paper
DOI: 10.1039/B709198B
Citation: Phys. Chem. Chem. Phys., 2007,9, 5644-5648
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    Molecular magnetic properties of heteroporphyrins: a theoretical analysis

    P. Campomanes, M. I. Menéndez, G. I. Cárdenas-Jirón and T. L. Sordo, Phys. Chem. Chem. Phys., 2007, 9, 5644
    DOI: 10.1039/B709198B

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