Analysis of 109Ag MAS NMR Chemical Shieldings Observed in AgxCu1−xI Crystals

109Ag NMR signals in AgxCu1−xI crystals were shifted to a low field relative to that in solid AgI with decreasing the unit cell constant analogously to 63Cu MAS NMR signals reported in a previous study. The observed chemical shieldings were analysed using the results of Ag and Cu NMR shielding calculations of tetrahedral (Td) MI43− (M = Ag, Cu) complex ions with the ab initio GAUSSIAN 94 program using a double-ζ basis set for the Ag, Cu, and I atoms. Since the shift is explained dominantly by the paramagnetic shielding term, which depends on the d-hole and p-electron densities in Ag or Cu atoms for the MI43− complex ions, the observed 109Ag shift moved to a low field with decreasing the lattice constant, corresponding to an increase in the d-hole and p-electron densities for AgI43− (RAg–I = 2.68, 2.73, 2.77 Å) relative to the AgI43− (RAg–I = 2.81Å) ion.