The mixed-valent indium chalcogenides InTe, In 4 Se 3 , In 4 Te 3 , In 6 S 7 and In 6 Se 7 were studied together with b-In 2 S 3 and TlInS 2 by In and Te K-edge EXAFS spectroscopy. These well-characterized crystalline solids were chosen as model systems to assess the general applicability of EXAFS for structural studies of first order mixedvalent solids containing indium. The question was whether the interatomic distances and coordination numbers derived from EXAFS data could be used for a basic structural characterization in the sense of ªstructural fingerprintsº to identify the indium species present in a given sample. Indium species in the samples comprised In + , In 3 , (In 2 ) 4 and (In 3 ) 5 , with up to 3 of them being simultaneously present. While the analysis of compounds with only one indium species was possible with high accuracy, it was impossible to interpret the EXAFS data of complex mixed-valent solids containing three different indium species (e.g. In , In 3 , (In 2 ) 4 ) without prior knowledge of the crystal structures. Intermediate cases are those compounds in which two indium species are present, e.g. In 3 in tetrahedral and octahedral coordination or In in a highly regular coordination accompanied by In 3 . In conclusion, EXAFS measurements alone can be a reliable basis for structural discussions beyond the first coordination sphere only for compounds of moderate complexity. In most cases prior information of structural data from single crystals or other sources is necessary. This is particularly relevant for future experiments with amorphous or polycrystalline samples that cannot be studied with standard diffraction techniques.

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