Ion Environments in Mn2+-Doped Polyelectrolyte Complexes: Dilute Magnetic Saloplastics

摘要

Amorphous hydrated complexes of the polyelectrolytes poly (styrene sulfonate) (PSS) and poly(diallyldimethylammonium) were doped with the spin-5/2 ion Mn2+. X-band electron paramagnetic resonance (EPR) measurements of the Mn2+ spins within these stoichiometric polyelectrolyte complexes (PECs) revealed an octahedral coordination environment, similar to that observed in aqueous solutions of Mn2+. This octahedral symmetry of the [Mn(H2O)(6)](2+) complexes, observed in fully hydrated PECs, is somewhat distorted because of the wide range of ion pairs possible with the sulfonate group on PSS. As the Mn2+ concentration was increased, the linewidths broadened, indicating the dominance of dipolar broadening over exchange narrowing in determining the linewidths; that is, any exchange narrowing was masked by the large dipolar broadening. The calculated linewidths were used to estimate the strengths of the dipolar interactions, and hence the distances between the Mn2+ spins, on the basis of a simple model of regularly spaced spins. The distances calculated by this method were roughly comparable to the geometric average distances calculated on the basis of the Mn2+ concentrations and densities of the doped PEC samples. From a comparison of their EPR spectra, the ion environments in the doped, fully hydrated PECs were found to be similar to those in hydrated classical ion exchange resins. EPR spectra before and after drying of the PECs indicate the replacement of octahedrally coordinated water by oxide anions from the polyanion chain and the corresponding loss of the symmetric environment of Mn2+ ions.