On the Structure of a Thiolated Gold Cluster: Au44(SR)282-

Many thiolate-protected gold clusters prepared by wet-chemistry show abundances of certain compositions which can be explained by the shell-closing of the superatom orbitals 1S, 1P, 1D, ... , leading to magic-number series 2, 8, 18, 20, 34, 58, etc. One recently isolated such cluster, Au-44(SPh)(28)(2-), is a potential candidate for the magic number 18, although its structure has not been determined. Applying the "divide-and-protect" concept and recent knowledge obtained from the structures of Au-25(SR)(18)(-) and Au-102(SR)(44) (-SR being a thiolate group), we compare two structural models for the Au-44(SR)(28)(2-) cluster. We have optimized their structures, computed powder X-ray diffraction patterns and optical absorption spectra, and performed the superatom analysis on them. The model featuring the -RS-Au-SR- and -RS-Au-SR-Au-SR- motifs in the protective layer shows better energetic stability and agreement with the experimental XRD pattern than the other model which has a protective layer including longer, polymeric RS(AuSR)(x) motifs. However, the computed optical spectra for both models are quite different from the experimental one. Our models here can serve as benchmarks for further proposals of Au-44(SR)(28)(2-) cluster structures.