Spectroscopic CW-EPR and HYSCORE investigations of Cu2+ and O-2(-) species in copper doped nanoporous calcium aluminate (12CaO center dot 7Al(2)O(3))

Continuous wave (CW) and pulse electron paramagnetic resonance in a variant of hyperfine sublevel correlation spectroscopy (HYSCORE) were used for obtaining structural information concerning speciation and local environment of alien Cu2+ and native O-2(-) ions encaged in copper doped nanoporous 12CaO center dot 7Al(2)O(3) (mayenite). The samples were prepared by a solid-state reaction and characterized by means of XRD, SEM, and Raman techniques. X-Band CW-EPR spectra showed that three different Cu2+ species together with paramagnetic extraframework O-2(-) anions were present in the mayenite sample, whereas extraframework OH- anions were revealed by Raman spectroscopy. Al-27 HYSCORE provided evidence for the interaction of Cu2+ ions with the mayenite framework. Superhyperfine interaction of the Cu2+ ions with proximal (d(Cu-OH) = 2.4 angstrom) and distal (d(Cu-OH) = 5.0 angstrom) OH- anions, located in the same and the nearby cage, respectively, was resolved by means of H-1 HYSCORE spectra. A different situation held for the encaged O-2(-) radicals found to be sitting on the Ca2+ ions. They exhibited only a weak superhyperfine interaction of 1 MHz with the Al-27(3+) framework ions.