X-ray diffraction study on the aggregate structure of 5,10,15,20-tetra(4-sulfophenyl)porphinatopalladium(II)(4-) in aqueous solution

Abstract

The aggregate structure of 5,10,15,20-tetra(4-sulfophenyl)porphinatopalladium(II) ion (PdTPPS^4–) in aqueous solution has been investigated in terms of the distance between the porphyrin monomers, by use of absorption spectroscopy, paramagnetic relaxation of NMR signals, and an isomorphic substitution method for X-ray diffraction of the solution. From absorption spectroscopy results it was concluded that the aggregate was regarded as a dimer arising from hydrophobic attraction between the porphyrin rings. Paramagnetic effects on the longitudinal relaxation time (T₁) for ¹³C NMR of PdTPPS^4– by the addition of 5,10,15,20-tetra(4-sulfophenyl)porphinatocopper(II)(CuTPPS^4–) suggested that the paramagnetic centre was located along a C₄-axis of PdTPPS^4– in a PdTPPS^4––CuTPPS^4– dimer. The dimer of PdTPPS^4– was determined to have a twisted face-to-face stacked structure (D_4d) at a distance of 4.1 Å by the isomorphic substituted X-ray diffraction study on PdTPPS^4– and CuTPPS^4– solutions.