CATALYSIS ON POLYMER SUPPORTS - ESR OF MO(V) DISPERSED IN POLY(ACRYLIC ACID) MATRICES

ESR spectra of molybdenum complexes obtained by dispersion of MoCl5 in a poly(acrylic acid) (PAA) matrix were interpreted and lead to a deta iled description of the ligands around the paramagnetic Mo(V) center. The specific bonding of the cation to the support is sensitive to the details of sample preparation, thermal treatment, and exposure to adso rbates. The most important factor that controls the type of complex fo rmed is the temperature. The five different Mo(V) complexes that were identified reflect the progressive replacement of chlorine ligands by oxygen ligands from the polymer in activated samples, and by water in samples exposed to water vapor after activation of the polymer contain ing MoCl5. After activation at 373 K molybdenum is linked to the polym er matrix via mono- and bidentate oxygen ligands, but still contains c hlorine ligands. After activation at 523 K, however, all chlorine liga nds appear to be replaced by oxygen ligands from the polymer support. Exposure to water vapor leads to replacement of one oxygen ligand arou nd the cation by oxygen from water. In the PAA matrix the Mo-Cl bond i s resistant to hydrolysis and to dioxygen, indicating the strong bondi ng to the matrix and the presence of coordinatively saturated octahedr al Mo(V) complexes.