Evidence for an Antiferromagnetic Transition in a Zeolite-Supported Cubic Lattice ofFCenters

Evidence for a bcc lattice of $F$ centers in sodium-electro-sodalite (SES), synthesized by exposing dehydrated sodalite to sodium vapor, is presented. A high electron spin density in SES produces isotropic contact shifts in nuclear magnetic resonance (NMR) spectra of the framework nuclei whose magnitude is a discrete function of local electron density. Strong exchange coupling between unpaired electrons gives rise to an antiferromagnetic phase transition in SES at $T_N=48\mathrm{}\pm 2\mathrm{K}$, providing the first example of an $s-\mathrm{electron}$ antiferromagnet.