Hyperfine interactions between randomly distributed F-center electrons and the surrounding magnetic nuclei in mixed Cl/electrosodalite, Na8[Al6Si6O24]Clx·(e–)2–x, gave rise to multiple nuclear magnetic resonances due to quantized variations in the local electron density at the nuclear site. This permitted one not only to account for the number of F centers surrounding a crystallographic site, but also to estimate the percentage of cages filled with F centers and their spatial distribution. Complete assignments of 23Na, 27Al and 35Cl magic-angle spinning nuclear magnetic resonance spectra were provided and the nuclear magnetic resonance evidence for spin correlation effects of interacting F-center electrons was presented. It was proposed that the spin pairing was a general feature of paramagnetic cage-structures with s-like electrons, owing it to the Pauli exclusion principle.

NMR Study of Interacting F Centers in Na8[Al6Si6O24]Cl2 Sodalite. H.Trill, H.Eckert, V.I.Srdanov: Physical Review B, 2005, 71[1], 014412 (6pp)