Local Structure of Amorphous Organotin Sulfide Clusters by Low‐Energy X‐Ray Absorption Fine Structure

The local structure of four amorphous organotin sulfide compounds exhibiting nonlinear optical (NLO) properties is investigated by low‐energy X‐ray absorption spectroscopy (XANES and EXAFS). The basic structural motif of a heteroadamantane cluster with different organic substituents is confirmed by the experiments and by comparison with computer simulations of the near‐edge structure. Essential information is obtained on a special role of the nonaromatic but electron‐rich cyclopentadienyl substituents, which are able to affect the structure of the heteroadamantane cluster core. The EXAFS fits also indicate a structural distinction between two groups within these compounds, which exhibit fundamentally different NLO responses: compounds that show a second harmonic generation can be described well using the single‐molecule approach, whereas the compounds exhibiting the generation of a supercontinuum manifest additional structural contributions.