Stability of Cu(II)- and Fe(III)-porphyrins on montmorillonite clay: An X-ray absorption study

The Cu(II) and Fe(III) complexes of water-soluble tetrakis(N,N,N-trimethylanilinium)porphyrin (TTAP) and tetrakis(N-methylpyridyl)porphyrin (TMPyP) were placed within the interlayers of Ca(II)-montmorillonite through ion exchange. The free base forms of the porphyrins were also added to samples of Cu(II)- and Fe(III)-montmorillonites. X-ray absorption spectroscopy (XAS), both X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS), were used to monitor the fate of the metal ions. The Cu(II)-metalloporphyrins do not demetalate upon contact with the acidic montmorillonite support. The XAS data also suggest that Fe(III)-porphyrin complexes are stable on smectite supports. XANES data demonstrate that the free base porphyrin TTAP metalates on the surface of a Cu(II)-exchanged clay to form a stable Cu(II)-porphyrin-clay complex.