Analysis of Ag-109 MAS NMR chemical shieldings observed in AgxCu1-xI crystals

Ag-109 NMR signals in AgCu1-xI crystals were shifted to a low field relativ e to that in solid AgI with decreasing the unit cell constant analogously t o Cu-63 MAS NMR signals reported in a previous study. The observed chemical shieldings were analysed using the results of Ag and Cu NMR shielding calc ulations of tetrahedral (T-d) MI43- (M = Ag, Cu) complex ions with the ab i nitio GAUSSIAN 94 program using a double-zeta basis set for the Ag, Cu, and I atoms. Since the shift is explained dominantly by the paramagnetic shiel ding term, which depends on the d-hole and p-electron densities in Ag or Cu atoms for the MI43- complex ions, the observed Ag-109 shift moved to a low field with decreasing the lattice constant, corresponding to an increase i n the d-hole and p-electron densities for AgI43- (RAg-I = 2.68, 2.73, 2.77 Angstrom) relative to the AgI43- (RAg-I = 2.81 Angstrom) ion.