Gold Valence in (AuI3)0.25Bi2Sr2CaCu2Oy by XPS and XANES Spectroscopy

The oxidation state of Au in AuI 3 intercalated into the interlayer space of Bi 2 Sr 2 CaCuO 2 O y 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 AuI 3 2- (Munzarova and Hoffmann, J. Am. Chem. Soc. 2002, 124, 5542). Here, we report the clear experimental evidences on the presence of AuI 3 2- through Au L 3 - and I L 1 -edge XANES spectroscopic studies. The Au L 3 -edge XANES spectrum of (AuI 3 ) 0.25 Bi 2 Sr 2 CaCu 2 O y undoubtedly shows that its adsorption edge energy is very close to that of AuI. Furthermore, the coordination of Au 1+ with I -1 in the D 3 h symmetry is well supported by the absence of any white line feature in the I L 1 -edge XANES spectrum.