Effects of Axial Ligands on the Formation of a Layered Structure in Mono- and Di-Cationic Charged Tetraphenylporphyrinatoantimony(V)/Synthetic Clay Composites

Abstract

Abstract Novel metalloporphyrin–clay composites were prepared from a synthetic clay (Sumecton SA: SSA) and cationic tetraphenylporphyrinatoantimony(V) bromide (SbTPP, 1–4) having various axial ligands. Both the crystal structure for SbTPP–SSA composites and the adsorption behaviors of SbTPP into SSA sheets are investigated regarding the relation to the structure of an axial ligand at SbTPP by measuring the X-ray diffraction (XRD), IR, UV–vis, and fluorescence spectroscopy. The XRD analysis revealed that powdered SbTPP–SSA composites could take a layered structure for 1, and an amorphous structure for 2, respectively. The IR spectrum of naked SSA showed a broad absorption band around 3000–3600 cm−1, which can probably be assigned as some adsorbed water molecules onto SSA. The intensity of the broad absorption band became weaker with an increase of the loading level (%LL), which was defined as a ratio of the concentration of the cationic sites of 1–4 to the concentration of anionic sites of SSA. The band completely disappeared at 100%LL in both 2–SSA and 4–SSA composites with the amorphous structure, whereas the band remained even at 100%LL in both 1–SSA and 3–SSA composites with the layered structure. Information about an aggregation state of 1–4 into SSA was obtained by measuring both the UV–vis absorption spectra of 1–4 in an aqueous colloidal clay solution and the fluorescence spectra of SbTPP–SSA composites in the solid state by using a confocal laser scanning fluorescence microscope. Each spectral data indicated that the ammonium cationic part on an axial ligand of 1 only led to effective non-aggregated adsorption onto SSA sheets, while 2–4 were located with the aggregated state on SSA sheets. These results also support that an axial ligand structure can control not only the formation of the crystal structure, but also the adsorption behaviors with aggregation or non-aggregation onto SSA sheets.