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Herein we present the first Mn–K edge EXAFS spectra recorded for manganese(III)porphyrin catalysts containing [Mn{T(4- N -MePy)P}(L) n ] 5+ (where L = oxygenated or nitrogenated axial ligands, n = 1 or 2) grafted onto modified silica-surfaces with propylimidazole, IPG ( 3 ), sulfonatophenyl, SiSO 3 − ( 4 ), and both, SiSO 3 − IPG ( 5 ), where T(4- N -MePy)P is the ligand 5,10,15,20-tetra(4- N -methylpyridyl)porphyrinate. From the data analysis and the refinement results, we have obtained the following structural information concerning to the coordination environment around the Mn(III) ion: four Mn–N at 2.00 A and two Mn–N/O axial at 2.26 A for 3 ; four Mn–N at 2.03 A and two Mn–O axial at 2.27 A for 4 , and four Mn–N at 2.02 A and two Mn–N/O axial at 2.28 A for 5 . Correlations of EXAFS data with UV–vis spectra pattern and other properties such as colors of the materials allowed distinguishing between materials 3 , 4 and 5 . Materials 4 and 5 belong to the same category, which involves ionic complex–support interaction. Furthermore, there are evidences for the coordination of the imidazolic ligand to the manganese(III) ion in 3 and 5 from qualitative analysis of XANES data. In the case of the catalyst 5 , bearing both sulfonate and imidazole as functional groups, we have suggested that the nature of the [Mn{T(4- N -MePy)P}(L) n ] 5+ –support interaction is predominantly of ionic character, even though the existence of Mn–imidazole bonds can be detected. |
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