Gold valence in (AuI3)0.25Bi2Sr2CaCu2Oy by XPS and XANES spectroscopy

The oxidation state of Au in AuI3 intercalated into the interlayer space of Bi2Sr2CaCuO2Oy high T-c superconducting phase still remains unconfirmed due to lack of unequivocal experimental evidence, although recent theoretical studies revealed the +1 oxidation state of Au in the form of AuI32- (Munzarova and Hoffmann, J. Am. Chem. Soc. 2002, 124, 5542). Here, we report the clear experimental evidences on the presence of AuI32- through Au L-3- and I L-1-edge XANES spectroscopic studies. The Au L-3-edge XANES spectrum of (AuI3)(0.25)Bi2Sr2CaCu2Oy undoubtedly shows that its adsorption edge energy is very close to that of AuI. Furthermore, the coordination of Au1+ with I-1 in the D-3h symmetry is well supported by the absence of any white line feature in the I L-1-edge XANES spectrum.