Chiral and Achiral Crystal Structures of Au 25 (PET) 18 0 Reveal Effects of Ligand Rotational Isomerization on Optoelectronic Properties.

The crystal structures of 4 ligand-rotational isomers of Au 25 (PET) 18 are presented. Two new ligand-rotational isomers are revealed, and two higher-quality structures (allowing complete solution of the ligand shell) of previously solved Au 25 (PET) 18 clusters are also presented. One of the structures lacks an inversion center, making it the first chiral Au 25 (SR) 18 structure solved. These structures combined with previously published Au 25 (SR) 18 structures enable an analysis of the empirical ligand conformation landscape for Au 25 (SR) 18 clusters. This analysis shows that the dihedral angles within the PET ligand are restricted to certain observable values, and also that the dihedral angle values are interdependent, in a manner reminiscent of biomolecule dihedral angles such as those in proteins and DNA. The influence of ligand conformational isomerism on optical and electronic properties was calculated, revealing that the ligand conformations affect the nanocluster absorption spectrum, which potentially provides a way to distinguish between isomers at low temperature.