Molecular complexation of meso-tetraphenylporphyrins with SO2

When para-substituted meso-tetraphenylporphyrins were reacted with SO2, only 2:1 (donor:acceptor) molecular complexes were produced. 1H NMR, IR, UV–vis and elemental analysis indicated that the porphyrins act as electron donors and that two SO2 molecules (as electron acceptors) are bound to the lone electron pairs of the pyrrolenine nitrogens in the porphyrin. Two d orbitals of the sulfur atoms accept the nitrogen lone pairs and the two SO2 molecules are located above and below the porphyrin. There are two hydrogen bonds present between two pyrrole NH and SO2 molecules.