Features of the microstructure of gold nanoparticles inside cavities of cucurbit[7]uril according to XAFS spectra

The Au$L_3$ X-ray absorption fine structure (XAFS) spectra have been measured for gold nanoparticles with the calibrated size $d_{\text{Au}}\sim1$ nm in the cavities of cucurbit[7]uril molecules. The features of their electronic structure and microstructure have been characterized. It has been found that gold clusters in cavities of cucurbit[7]uril are characterized by smaller (by ${\sim}\,(0.01$–$0.02)$ Å) interatomic distances and a noticeably larger (by a factor of $3$ at $12$ K) Debye-Waller factor as compared to bulk gold. Analysis of the experimental results and their comparison with the model calculations show that the special properties of atoms on the surface of small metal (gold) particles are not determined by their position at the vertices and edges of small clusters; they are likely attributed to the structural disorder, deformations, and stresses, which increase with a decrease in the size of the particles.