I-129 and Au-197 Mossbauer spectroscopy of AuI and AgAuI2

Mossbauer spectroscopy of I-129 and Au-197 nuclei has been applied for AuI and AgAuI2 to clarify the electronic structures of the gold and iodine atoms, and to investigate the nature of the Au-I bonds. In the I-129 Mossbauer spectra the sign of e(2)qQ is positive for AuI, whereas the sign is negative for AgAuI2. This is attributable to the difference in molecular structures: The iodine atom in AuI is bridged by two gold atoms and in AgAuI2 the iodine is terminal. The Au-197 Mossbauer spectra suggest that the Au-I bond in AgAuI2 is more covalent than that in AuI. We have revealed that AgAuI2 consists of Ag+ and linear [I-Au-I](-) units from the Rietveld refinement of the X-ray powder diffraction pattern.