Nuclear Magnetic Resonance Study of Li3Sb, Na3Sb, and Na3As Powders

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Abstract
NMR spectra showing quadrupole splittings were obtained for 7Li and 23Na in some I–V intermetallic compounds. All are hexagonal and are reputed to be semiconductors. The Li (Na) atoms lie in two sites: planes containing the Sb (As) atoms (site 1) and parallel planes containing only the Li (Na) atoms (site 2). Coupling constants for sites 1 and 2 are, respectively: 75.2 and 17.6 kc/sec in Li3Sb; 1.49 and 0.44 Mc/sec in Na3Sb; 1.70 and 0.53 Mc/sec in Na3As. Asymmetry parameters are zero. Small magnetic shifts appeared in Na3Sb and Na3As. Measured coupling constants are not consistent with an ionic model. Covalent bonding must exist. Suchet's model, of form Na(2)2[Na(1)2−As2+], suggests sp2 hybrid bonds in the Na–As plane consistent with its structure. However, contrary to Suchet, the Na(2) atoms may not exist as Na2 molecules but as atoms with zero charge. Such models do not correlate well with the semiconductivity property. Another model, of the form Na(2)21+[Na(1)1−As1−], was considered. Its bounding in the Na–As plane is via sp and p2 hybrids and this is consistent with the semiconductivity.