Synthesis of hybrid organo-mineral materials: Anionic tetraphenylporphyrins in layered double hydroxides

meso-Tetrakis(p-carboxyphenyl)porphyrin in (pTCPP), the atropoisomer (alpha alpha alpha alpha) of meso-tetrakis(o-carboxyphenyl) porphyrin (oTCPP), and the ammonium salt of the meso-tetrakis(p-sulfonatophenyl)porphyrin (noted pTSPP) were intercalated into [Zn-Al] layered double hydroxide (LDH) using different preparative methods. Coprecipitation at constant pH in a porphyrinic solution of zinc and aluminum salts or anionic exchange of pTCPP on a [Zn-Al-Cl] precursor led to pure LDH phases, while products obtained from the calcination-reconstruction method on a [Zn-Al-Cl] precursor contain a significant amount of ZnO. Powder X-ray diffraction and UV-visible diffuse reflectance spectroscopy of LDH intercalated with pTCPP, oTCPP, and pTSPP show complete intercalation. Interlayer spacing ranging from 18.54 Angstrom for [Zn-Al-oTCPP] to 22.91 Angstrom for [Zn-Al-pTSPP] and 22.73 Angstrom for [Zn-Al-pTCPP], determined from PXRD patterns, reveal different orientations of the anionic macrocyles between the hyroxylated layers. This selective arrangement is discussed in terms of layer charge density, isomeric substitution of the anionic groups on the meso tetraphenylporphyrins, and guest molecules and host matrix interactions.